6.2.pdf DGCA AME MODULE 6.2 ppt NON FERROUS METALS
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About This Presentation
6.2.pdf DGCA AME MODULE 6.2 ppt NON FERROUS METALS
Slide Content
MODULE 6
6.2 NON FERROUS METALS
6.2 NON FERROUS METALS
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Aluminium
Production
Mechanical Properties
Aluminium Alloys
Metal Condition
Corrosion Protection
Heat Treatment Processes
Heat Treatment Indication
Specifications
Identification Markings
Cast Aluminium
Magnesium and Magnesium Alloys *(* a metal made by combining two or more metallic elements, especially to give
greater strength or resistance to corrosion)
Titanium
Nickel and its Alloys
Electrical Resistance Alloys For Use at High Temperatures
Low Expansion Alloys
High Temperature Corrosion Resistant Alloys
Monel Metal
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Aluminium
Production
Mechanical Properties
Aluminium Alloys
Metal Condition
Corrosion Protection
Heat Treatment Processes
Heat Treatment Indication
Specifications
Identification Markings
Cast Aluminium
Magnesium and Magnesium Alloys *(* a metal made by combining two or more metallic elements, especially to give
greater strength or resistance to corrosion)
Titanium
Nickel and its Alloys
Electrical Resistance Alloys For Use at High Temperatures
Low Expansion Alloys
High Temperature Corrosion Resistant Alloys
Monel Metal
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Copper and its Alloys
Tungum
Brass Bronze
Lead and its Alloys
White Bearing Metals
Miscellaneous Metals
Depleted Uranium
Tungsten
Cadmium
Chromium
Metal Fatigue
General
Fatigue Life and Safety Margin
Shot Peening
Rotopeening
Cold Working
(b) Testing of Non-Ferrous Materials
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Copper and its Alloys
Tungum
Brass Bronze
Lead and its Alloys
White Bearing Metals
Miscellaneous Metals
Depleted Uranium
Tungsten
Cadmium
Chromium
Metal Fatigue
General
Fatigue Life and Safety Margin
Shot Peening
Rotopeening
Cold Working
(b) Testing of Non-Ferrous Materials
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The term “non-ferrous” refers to all metals which have elements other than
iron as their base or principal constituent. This group includes pure metals
such as aluminium, titanium, copper and magnesium, as well as alloyed
metals like brass, bronze, monel and babbit. Alloys of aluminium and
magnesium are referred to as Light Alloys.
Aluminium is the most important metal in aircraft engineering. Most modern
aircraft are constructed from aluminium alloys of one form or another.
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The term “non-ferrous” refers to all metals which have elements other than
iron as their base or principal constituent. This group includes pure metals
such as aluminium, titanium, copper and magnesium, as well as alloyed
metals like brass, bronze, monel and babbit. Alloys of aluminium and
magnesium are referred to as Light Alloys.
Aluminium is the most important metal in aircraft engineering. Most modern
aircraft are constructed from aluminium alloys of one form or another.
PRODUCTION
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Aluminium is derived from the red ore Bauxite, which is widely
distributed within the earth's crust. However, large deposits of
sufficiently high purity for commercial exploitation are located in
comparatively few places.
Bauxite is refined into aluminium oxide trihydrate (alumina) and
then electrolytically reduced into metallic aluminium. Two to three
tonnes of bauxite are required to produce one tonne of alumina
and two tonnes of alumina are required to produce one tonne of
aluminium metal.
2 - 3 tonnes bauxite ---> 1 tonne of alumina
2 tonnes of alumina ---> 1 tonne of aluminium metal
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Aluminium is derived from the red ore Bauxite, which is widely
distributed within the earth's crust. However, large deposits of
sufficiently high purity for commercial exploitation are located in
comparatively few places.
Bauxite is refined into aluminium oxide trihydrate (alumina) and
then electrolytically reduced into metallic aluminium. Two to three
tonnes of bauxite are required to produce one tonne of alumina
and two tonnes of alumina are required to produce one tonne of
aluminium metal.
2 - 3 tonnes bauxite ---> 1 tonne of alumina
2 tonnes of alumina ---> 1 tonne of aluminium metal
ALUMINIUM PRODUCTION PROCESS
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The aluminium industry relies on the Bayer process to produce alumina from
bauxite.
The bauxite is washed, ground and dissolved in caustic soda (sodium
hydroxide) at high pressure and temperature.
The resulting liquor contains a solution of sodium aluminate and un-
dissolved bauxite residues containing iron, silicon, and titanium.
These residues sink gradually to the bottom of the tank and are removed.
They are known as “red mud”.
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The aluminium industry relies on the Bayer process to produce alumina from
bauxite.
The bauxite is washed, ground and dissolved in caustic soda (sodium
hydroxide) at high pressure and temperature.
The resulting liquor contains a solution of sodium aluminate and un-
dissolved bauxite residues containing iron, silicon, and titanium.
These residues sink gradually to the bottom of the tank and are removed.
They are known as “red mud”.
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The clear sodium aluminate solution is pumped into a huge tank
called a precipitator.
Fine particles of alumina are added to seed the precipitation of
pure alumina particles as the liquor cools.
The particles sink to the bottom of the tank, are removed, and are
then passed through a rotary kiln at 1100°C to drive off the
chemically combined water.
The result is a white powder, pure alumina.
The caustic soda is returned to the start of the process and used
again.
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The clear sodium aluminate solution is pumped into a huge tank
called a precipitator.
Fine particles of alumina are added to seed the precipitation of
pure alumina particles as the liquor cools.
The particles sink to the bottom of the tank, are removed, and are
then passed through a rotary kiln at 1100°C to drive off the
chemically combined water.
The result is a white powder, pure alumina.
The caustic soda is returned to the start of the process and used
again.
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The aluminium reducing or 'smelting' process used is the Hall-Héroult
Process, invented in 1886.
The alumina powder is dissolved in an electrolytic bath of molten cryolite
(sodium aluminium fluoride) within a large carbon or graphite lined steel
container known as a “pot”.
An electric current is passed through the electrolyte at low voltage, but very
high current, typically 150,000 amperes.
The current flows between carbon anodes (positive), made of petroleum
coke and pitch, and a cathode (negative), formed lining of the pot, and heats
the solution.
Oxygen is given off at the anodes, which burn as a result, and need to be
replaced quite often.
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The aluminium reducing or 'smelting' process used is the Hall-Héroult
Process, invented in 1886.
The alumina powder is dissolved in an electrolytic bath of molten cryolite
(sodium aluminium fluoride) within a large carbon or graphite lined steel
container known as a “pot”.
An electric current is passed through the electrolyte at low voltage, but very
high current, typically 150,000 amperes.
The current flows between carbon anodes (positive), made of petroleum
coke and pitch, and a cathode (negative), formed lining of the pot, and heats
the solution.
Oxygen is given off at the anodes, which burn as a result, and need to be
replaced quite often.
Molten aluminium particles,
being positively charged, are
attracted to the lining of the
furnace and collect at the
bottom of the pot to be
siphoned off periodically,
taken to a holding furnace,
often but not always blended
to an alloy specification,
cleaned and then generally
cast.
being positively charged, are
attracted to the lining of the
furnace and collect at the
bottom of the pot to be
siphoned off periodically,
taken to a holding furnace,
often but not always blended
to an alloy specification,
cleaned and then generally
cast.
Because of the nature of the process,
abundant electrical power must be
available. Thus production plants are
situated close to the sources of electricity
such as hydroelectric or nuclear power
stations, and not normally near the bauxite
mines.Aluminium is formed at about
900°C, but once formed has a melting
point of only 660°C. In some smelters this
spare heat is used to melt recycled metal.Recycled aluminium requires only 5 per cent
of the energy required to make “new”
aluminium. Blending recycled metal with
new metal allows considerable energy
savings, as well as the efficient use of
process heat. There is no difference
between primary and recycled aluminium
in terms of quality or properties.
Most smelters produce aluminium of 99.7%
purity, which is acceptable for most
applications. However, super purity
aluminium (99.99%) is used for some
special applications, typically those where
high ductility or conductivity is required.
The marginal difference in the purities of
smelter grade aluminium and super purity
aluminium results in significant changes in
the properties of the metal.
abundant electrical power must be
available. Thus production plants are
situated close to the sources of electricity
such as hydroelectric or nuclear power
stations, and not normally near the bauxite
mines.Aluminium is formed at about
900°C, but once formed has a melting
point of only 660°C. In some smelters this
spare heat is used to melt recycled metal.Recycled aluminium requires only 5 per cent
of the energy required to make “new”
aluminium. Blending recycled metal with
new metal allows considerable energy
savings, as well as the efficient use of
process heat. There is no difference
between primary and recycled aluminium
in terms of quality or properties.
Most smelters produce aluminium of 99.7%
purity, which is acceptable for most
applications. However, super purity
aluminium (99.99%) is used for some
special applications, typically those where
high ductility or conductivity is required.
The marginal difference in the purities of
smelter grade aluminium and super purity
aluminium results in significant changes in
the properties of the metal.
MECHANICAL PROPERTIES - ALUMINIUM
Pure aluminium is a silvery-white metal which
is soft and ductile.
It has a melting point of 660°C and a specific
gravity of about 2.7, i.e. nearly one third
that of steel or copper.
It is resistant to atmospheric corrosion owing
to the presence of an oxide film which
forms naturally on its surface. Aluminium
is also resistant to dilute acids, but alkalis
attack and destroy the oxide film, causing
corrosion.
Because of its properties, aluminium and its
alloys can be formed into a finished
product in many ways. These generally fall
into two classes; Wrought or worked and
Cast or moulded.
The metal is a good conductor of electricity
and its electrical conductivity is about 65%
that of copper.
It also conducts heat well and is widely used
in heat exchangers, aircraft, food
production and chemical plant.
It is non-magnetic and non-sparking, making
it suitable for use as a shielding metal for
certain electrical equipment.
Cold-working, such as rolling, will increase the
strength of the metal and its alloys,
sometimes almost doubling their original
values.
Wrought aluminium can be bent or folded,
stamped, hammered, drawn, rolled,
machined, forged, extruded, brazed or
welded into a wide variety of objects.
Pure aluminium is a silvery-white metal which
is soft and ductile.
It has a melting point of 660°C and a specific
gravity of about 2.7, i.e. nearly one third
that of steel or copper.
It is resistant to atmospheric corrosion owing
to the presence of an oxide film which
forms naturally on its surface. Aluminium
is also resistant to dilute acids, but alkalis
attack and destroy the oxide film, causing
corrosion.
Because of its properties, aluminium and its
alloys can be formed into a finished
product in many ways. These generally fall
into two classes; Wrought or worked and
Cast or moulded.
The metal is a good conductor of electricity
and its electrical conductivity is about 65%
that of copper.
It also conducts heat well and is widely used
in heat exchangers, aircraft, food
production and chemical plant.
It is non-magnetic and non-sparking, making
it suitable for use as a shielding metal for
certain electrical equipment.
Cold-working, such as rolling, will increase the
strength of the metal and its alloys,
sometimes almost doubling their original
values.
Wrought aluminium can be bent or folded,
stamped, hammered, drawn, rolled,
machined, forged, extruded, brazed or
welded into a wide variety of objects.
ALUMINIUM ALLOYS
Aluminium can be Cast by any known foundry
process to practically any shape at a
comparatively low temperature.
As mentioned, the properties of aluminium
can be drastically improved by alloying it
with other elements.
Aluminium can be Cast by any known foundry
process to practically any shape at a
comparatively low temperature.
As mentioned, the properties of aluminium
can be drastically improved by alloying it
with other elements.
The first digit indicates the principle alloying
element. For example any alloy in the 2000
series such as 2117 or 2024 has copper as
its main alloying element. 7075 has zinc as
its main alloy.
The second digit identifies the alloy
modification. 0 indicates that the alloy is
original. 1 indicates that the alloy has been
modified once etc. The 3rd and 4th digits
identify the specific aluminium alloy.
In the case of 2024, the alloy consists of
about 4.5% copper, 1.5% magnesium, 0.6%
manganese,
element. For example any alloy in the 2000
series such as 2117 or 2024 has copper as
its main alloying element. 7075 has zinc as
its main alloy.
The second digit identifies the alloy
modification. 0 indicates that the alloy is
original. 1 indicates that the alloy has been
modified once etc. The 3rd and 4th digits
identify the specific aluminium alloy.
In the case of 2024, the alloy consists of
about 4.5% copper, 1.5% magnesium, 0.6%
manganese,
Various aluminium alloys are used for aircraft
fabrication:
1000 series. Aluminium of 99 percent or
higher purity has practically no application
in the aerospace industry. These alloys are
characterised by excellent corrosion
resistance, high thermal and electrical
conductivity, low mechanical properties,
and excellent workability.
Moderate increases in strength can be
obtained by strain hardening. Soft 1100
rivets are used in non-structural
applications.
fabrication:
1000 series. Aluminium of 99 percent or
higher purity has practically no application
in the aerospace industry. These alloys are
characterised by excellent corrosion
resistance, high thermal and electrical
conductivity, low mechanical properties,
and excellent workability.
Moderate increases in strength can be
obtained by strain hardening. Soft 1100
rivets are used in non-structural
applications.
2000 series: Copper is the principal alloying
element in this group. These alloys require
solution heat-treatment to obtain optimum
properties; in the heat-treated condition
mechanical properties are similar to, and
sometimes exceed, those of mild steel. In
some instances artificial aging is
employed to further increase the
mechanical properties. This treatment
materially increases yield strength. These
alloys in the form of sheet are usually clad
with a high-purity alloy. Alloy 2024 is
perhaps the best known and most widely
used aircraft alloy. Most aircraft rivets are
of alloy 2117.
3000 series: Manganese is the major alloying
element of alloys in this group, which are
generally non-heat treatable. One of these
is 3003, which has limited use as a
general-purpose alloy for moderate-
strength applications requiring good
workability, such as cowlings and non-
structural parts. Alloy 3003 is easy to weld.4000 series: This alloy series is seldom used
in the aerospace industry.
element in this group. These alloys require
solution heat-treatment to obtain optimum
properties; in the heat-treated condition
mechanical properties are similar to, and
sometimes exceed, those of mild steel. In
some instances artificial aging is
employed to further increase the
mechanical properties. This treatment
materially increases yield strength. These
alloys in the form of sheet are usually clad
with a high-purity alloy. Alloy 2024 is
perhaps the best known and most widely
used aircraft alloy. Most aircraft rivets are
of alloy 2117.
3000 series: Manganese is the major alloying
element of alloys in this group, which are
generally non-heat treatable. One of these
is 3003, which has limited use as a
general-purpose alloy for moderate-
strength applications requiring good
workability, such as cowlings and non-
structural parts. Alloy 3003 is easy to weld.4000 series: This alloy series is seldom used
in the aerospace industry.
5000 series: Magnesium is one of the most
effective and widely used alloying
elements for aluminium. When it is used
as the major alloying element, or with
manganese, the result is a moderate to
high strength non-heat treatable alloy.
Alloys in this series possess good welding
characteristics and good resistance to
corrosion in various atmospheres. It is
widely used for the fabrication of tanks
and fluid lines.
•6000 series: Alloys in this group contain
silicon and magnesium in approximate
proportions to form magnesium silicide,
thus making them heat treatable. The
major alloy in this series is 6061, one of
the most versatile of the heat-treatable
alloys. Though less strong than most of
the 2000 or 7000 alloys, the magnesium-
silicon (or magnesium-silicide) alloys
possess good formability and corrosion
resistance, with medium strength.
effective and widely used alloying
elements for aluminium. When it is used
as the major alloying element, or with
manganese, the result is a moderate to
high strength non-heat treatable alloy.
Alloys in this series possess good welding
characteristics and good resistance to
corrosion in various atmospheres. It is
widely used for the fabrication of tanks
and fluid lines.
•6000 series: Alloys in this group contain
silicon and magnesium in approximate
proportions to form magnesium silicide,
thus making them heat treatable. The
major alloy in this series is 6061, one of
the most versatile of the heat-treatable
alloys. Though less strong than most of
the 2000 or 7000 alloys, the magnesium-
silicon (or magnesium-silicide) alloys
possess good formability and corrosion
resistance, with medium strength.
7000 series: Zinc is the major alloying
element in this group, and when coupled
with a smaller percentage of magnesium
results in heat treatable alloys of very high
strength. Usually other elements, such as
copper and chromium, are also added in
small quantities. The outstanding member
of this group is 7075, which is among the
highest strength alloys available and is
used in airframe structures for highly
stressed parts.
8000 series. Of this group the Aluminium-
Lithium alloys are the most important for
the aviation industry. Having a low density,
lithium reduces the weight of the alloy
while offering strength comparable to the
7000 series and competes with carbon
composite material. It's development
problems and high cost have so far
prevented it's wide spread use in
commercial aviation.
element in this group, and when coupled
with a smaller percentage of magnesium
results in heat treatable alloys of very high
strength. Usually other elements, such as
copper and chromium, are also added in
small quantities. The outstanding member
of this group is 7075, which is among the
highest strength alloys available and is
used in airframe structures for highly
stressed parts.
8000 series. Of this group the Aluminium-
Lithium alloys are the most important for
the aviation industry. Having a low density,
lithium reduces the weight of the alloy
while offering strength comparable to the
7000 series and competes with carbon
composite material. It's development
problems and high cost have so far
prevented it's wide spread use in
commercial aviation.
Other terms which may be encountered
include;
Duralumin (or Dural) which was the original
aluminium/copper alloy patented in 1908
and formed the basis of the 2000 series
alloys.
Hiduminium - A family of British high
performance aluminium/copper/ nickel
alloys. Used for rivets, skins, castings and
forgings.
include;
Duralumin (or Dural) which was the original
aluminium/copper alloy patented in 1908
and formed the basis of the 2000 series
alloys.
Hiduminium - A family of British high
performance aluminium/copper/ nickel
alloys. Used for rivets, skins, castings and
forgings.
METAL CONDITION
•WORK HARDENING:
Like all metals, at a microscopic level,
aluminium is crystalline in structure. When
the metal is worked (cut, bent, stretched or
otherwise deformed) the crystals or grains
slide over each other at the “slip planes‟
formed by the crystal boundaries.
The crystals will also bend or distort, but as
they do, stresses form in them and the
structure will become more resistant to
movement and therefore harder.
This process is known as „Work' or 'Strain
Hardening‟.
If further work is done the stress becomes
too great, the crystals fail and the metal
will fracture and break.
•AGE HARDENING(solution treatment):
Alloys which have been heated may not
return to their normal cold level of
hardness straight away. It can take several
hours, days or weeks, depending on the
alloy and treatment applied, for the metal
to 'Age Harden' to its original state. This
allows work to be done to the metal before
its full strength is naturally restored.TEMPER:
Temper is the term used to describe the
condition of the metal with regard to its
workability. This includes the hardness,
malleability and ductility of the metal.
•WORK HARDENING:
Like all metals, at a microscopic level,
aluminium is crystalline in structure. When
the metal is worked (cut, bent, stretched or
otherwise deformed) the crystals or grains
slide over each other at the “slip planes‟
formed by the crystal boundaries.
The crystals will also bend or distort, but as
they do, stresses form in them and the
structure will become more resistant to
movement and therefore harder.
This process is known as „Work' or 'Strain
Hardening‟.
If further work is done the stress becomes
too great, the crystals fail and the metal
will fracture and break.
•AGE HARDENING(solution treatment):
Alloys which have been heated may not
return to their normal cold level of
hardness straight away. It can take several
hours, days or weeks, depending on the
alloy and treatment applied, for the metal
to 'Age Harden' to its original state. This
allows work to be done to the metal before
its full strength is naturally restored.TEMPER:
Temper is the term used to describe the
condition of the metal with regard to its
workability. This includes the hardness,
malleability and ductility of the metal.
CORROSION PROTECTION
Introducing other elements into aluminium to
form alloys reduces its corrosion resistant
characteristics, in some cases by quite a
large margin. Altering the crystal structure
by heating and working also affects these
properties.
Various chemical and electro-chemical
processes and coatings are used to
protect the finished product, and these will
be covered at a later date, however, sheet
aluminium alloy is often protected at
manufacture by 'Cladding'(a covering or
coating on a structure or material) it with a
layer of almost pure aluminium on each
side.
The cladding is cold rolled onto the alloy and
forms 5% of the total thickness on each
side of sheet material (up to 0.249 inch)
and 2.5% of the thickness of thicker plate
(over 0.250 inch) material, e.g. flat sheet
0.150 inch thick would have 0.0075 inch
clad on either side. This material is
produced under trade names such as
Alclad and Pureclad.
Introducing other elements into aluminium to
form alloys reduces its corrosion resistant
characteristics, in some cases by quite a
large margin. Altering the crystal structure
by heating and working also affects these
properties.
Various chemical and electro-chemical
processes and coatings are used to
protect the finished product, and these will
be covered at a later date, however, sheet
aluminium alloy is often protected at
manufacture by 'Cladding'(a covering or
coating on a structure or material) it with a
layer of almost pure aluminium on each
side.
The cladding is cold rolled onto the alloy and
forms 5% of the total thickness on each
side of sheet material (up to 0.249 inch)
and 2.5% of the thickness of thicker plate
(over 0.250 inch) material, e.g. flat sheet
0.150 inch thick would have 0.0075 inch
clad on either side. This material is
produced under trade names such as
Alclad and Pureclad.
HEAT TREATMENT PROCESS
Apart from work and age hardening, the
temper of aluminium alloy may be
modified by heat treatment processes,
each of which may be applied to some, but
not all alloys.
The heat is normally applied in an air or
muffle furnace, or a salt bath. The air
furnace circulates hot air around the work
piece and is normally electrically heated as
gas would introduce moisture. They are
particularly suitable for small parts and a
small furnace may be accommodated in
almost any workshop.A salt bath is a heated tank containing
mineral salts, typically 90% nitrate of soda
and 10% sodium nitrate, although others
may be used. These are solid at room
temperature and melt when heat is
applied.
Electricity is normally used to apply gradual
heat and prevent spattering an spitting as
the salts melt. Before emersion the work
piece should be thoroughly dried and water
kept away from the bath. Some salt
mixtures are also flammable.
The salt bath provides rapid and uniform
heating for large objects which may be
placed in a basket for emersion.
Small objects should be suspended on a wire
or placed in a perforated container. Work
pieces should not touch the sides of the
tank as the salt solution must be able to
circulate around them.
Apart from work and age hardening, the
temper of aluminium alloy may be
modified by heat treatment processes,
each of which may be applied to some, but
not all alloys.
The heat is normally applied in an air or
muffle furnace, or a salt bath. The air
furnace circulates hot air around the work
piece and is normally electrically heated as
gas would introduce moisture. They are
particularly suitable for small parts and a
small furnace may be accommodated in
almost any workshop.A salt bath is a heated tank containing
mineral salts, typically 90% nitrate of soda
and 10% sodium nitrate, although others
may be used. These are solid at room
temperature and melt when heat is
applied.
Electricity is normally used to apply gradual
heat and prevent spattering an spitting as
the salts melt. Before emersion the work
piece should be thoroughly dried and water
kept away from the bath. Some salt
mixtures are also flammable.
The salt bath provides rapid and uniform
heating for large objects which may be
placed in a basket for emersion.
Small objects should be suspended on a wire
or placed in a perforated container. Work
pieces should not touch the sides of the
tank as the salt solution must be able to
circulate around them.
Items removed from a salt bath must be
thoroughly cleaned to remove all residues.
Clad sheet material must not be heat treated
more than three times as migration of the
alloying elements into the cladding will
reduce both the strength of the core alloy
and the corrosion resistance of the sheet.
thoroughly cleaned to remove all residues.
Clad sheet material must not be heat treated
more than three times as migration of the
alloying elements into the cladding will
reduce both the strength of the core alloy
and the corrosion resistance of the sheet.
ANNEALING
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Heat and allow to cool slowly.
If metal which has become work hardened
is heated, the internal crystalline stresses
begin to dissipate and rearrangement of
the deformed structure starts. As the
temperature rises, the distorted original
grains disappear and new grains grow to
form a stress-free system. This
“recrystallisation‟ brings the metal to its
softest state. This process is known as
annealing and leaves the cooled metal in a
softened state so that further work can be
done.
These effects depend on time as well as
temperature. So that the change may be
completed quickly, it is usual to heat the
metal in air at a much higher temperature
(340ºC to 450ºC) than the minimum
necessary for recrystallisation. Apart from
convenience, this is done to avoid the
merging of crystals to form larger ones,
which is encouraged by, among other
factors, a long heating time. “Grain
growth‟, as it is called, impairs mechanical
properties. Alloys that are especially prone
to gain growth are sometimes annealed
more rapidly in molten salts at about
500ºC.
The heating and soaking times specified for
the alloy must be carefully observed to
prevent grain growth and all manipulation
should be completed within 24 hours of
annealing as age hardening will begin to
takeplace.
•
•
•
Heat and allow to cool slowly.
If metal which has become work hardened
is heated, the internal crystalline stresses
begin to dissipate and rearrangement of
the deformed structure starts. As the
temperature rises, the distorted original
grains disappear and new grains grow to
form a stress-free system. This
“recrystallisation‟ brings the metal to its
softest state. This process is known as
annealing and leaves the cooled metal in a
softened state so that further work can be
done.
These effects depend on time as well as
temperature. So that the change may be
completed quickly, it is usual to heat the
metal in air at a much higher temperature
(340ºC to 450ºC) than the minimum
necessary for recrystallisation. Apart from
convenience, this is done to avoid the
merging of crystals to form larger ones,
which is encouraged by, among other
factors, a long heating time. “Grain
growth‟, as it is called, impairs mechanical
properties. Alloys that are especially prone
to gain growth are sometimes annealed
more rapidly in molten salts at about
500ºC.
The heating and soaking times specified for
the alloy must be carefully observed to
prevent grain growth and all manipulation
should be completed within 24 hours of
annealing as age hardening will begin to
takeplace.
ANNEALING PROCESS
SOLUTION TREATMENT
Within the aluminium crystal structure some
alloying elements such as copper are
capable of being in a 'solid solution', a
matrix of aluminium atoms with copper
atoms dissolved in it.
An aluminium alloy containing 4% copper at
room temperature (21ºC) will have 0.5% of
the copper in solid solution with the
aluminium. The remaining 3.5% of copper
is chemically combined with the
aluminium to form the intermetallic
compound Cu Al2(copper aluminide).
The ability of copper to dissolve in aluminium
increases with temperature so that, as the
alloy is heated, the Cu Al2 is dissolved and
the 4% copper is in solid solution with the
aluminium at about 500ºC.
If the alloy is slowly cooled, the Cu Al2 will
gradually reappear as fairly large particles,
visible under the microscope. This coming
out of solution is termed 'precipitation'. At
room temperature only 0.5% of the copper
remains dissolved.
If, however, the alloy is quenched from 500°C,
the copper is 'frozen' in the solid solution
and no Cu Al2 is seen in the structure. In
this state the alloy is relatively soft and
malleable. This is known as Solution Heat
Treatment (SHT) or simply Solution
Treatment.
After a period of about two hours the copper
will begin to precipitate out of solution and
the tensile strength and hardness begin to
increase until, after about 5 days, these
properties are at a maximum. This is
known as “Age Hardening” .
Within the aluminium crystal structure some
alloying elements such as copper are
capable of being in a 'solid solution', a
matrix of aluminium atoms with copper
atoms dissolved in it.
An aluminium alloy containing 4% copper at
room temperature (21ºC) will have 0.5% of
the copper in solid solution with the
aluminium. The remaining 3.5% of copper
is chemically combined with the
aluminium to form the intermetallic
compound Cu Al2(copper aluminide).
The ability of copper to dissolve in aluminium
increases with temperature so that, as the
alloy is heated, the Cu Al2 is dissolved and
the 4% copper is in solid solution with the
aluminium at about 500ºC.
If the alloy is slowly cooled, the Cu Al2 will
gradually reappear as fairly large particles,
visible under the microscope. This coming
out of solution is termed 'precipitation'. At
room temperature only 0.5% of the copper
remains dissolved.
If, however, the alloy is quenched from 500°C,
the copper is 'frozen' in the solid solution
and no Cu Al2 is seen in the structure. In
this state the alloy is relatively soft and
malleable. This is known as Solution Heat
Treatment (SHT) or simply Solution
Treatment.
After a period of about two hours the copper
will begin to precipitate out of solution and
the tensile strength and hardness begin to
increase until, after about 5 days, these
properties are at a maximum. This is
known as “Age Hardening” .
As with annealing, the heating, soaking and
quenching must be carefully controlled as
they are time and temperature sensitive.
Quenching may be required to be done in
hot or boiling water to reduce quenching
stress.
quenching must be carefully controlled as
they are time and temperature sensitive.
Quenching may be required to be done in
hot or boiling water to reduce quenching
stress.
PRECIPITATION TREATMENT
In some alloys, the spontaneous ageing
process is complete after a few days at
room temperature. A greater degree of
precipitation and hardening than occurs
naturally can, in certain alloys, be induced
by heating to about 170ºC for ten hours or
so (time and temperature depending on
composition). This is called “Precipitation
Treatment‟ or “Artificial Ageing‟.During this hardening and strengthening
operation, precipitation of the soluble
constituents from the supersaturated solid
solution takes place. As precipitation
progresses, the strength of the material
increases, often by a series of peaks, until
a maximum is reached.
Precipitation Treatment controls the size and
distribution of the precipitates and in this
manner, the strength and hardness of the
alloy is increased beyond that achieved by
natural age hardening.
The ageing practices used depend upon many
properties other than strength. As a rule,
the artificially aged alloys are slightly over
aged to increase their resistance to
corrosion. This is especially true with the
artificially aged 7000 series alloys that are
susceptible to intergranular corrosion
when aged to peak strength.
In some alloys, the spontaneous ageing
process is complete after a few days at
room temperature. A greater degree of
precipitation and hardening than occurs
naturally can, in certain alloys, be induced
by heating to about 170ºC for ten hours or
so (time and temperature depending on
composition). This is called “Precipitation
Treatment‟ or “Artificial Ageing‟.During this hardening and strengthening
operation, precipitation of the soluble
constituents from the supersaturated solid
solution takes place. As precipitation
progresses, the strength of the material
increases, often by a series of peaks, until
a maximum is reached.
Precipitation Treatment controls the size and
distribution of the precipitates and in this
manner, the strength and hardness of the
alloy is increased beyond that achieved by
natural age hardening.
The ageing practices used depend upon many
properties other than strength. As a rule,
the artificially aged alloys are slightly over
aged to increase their resistance to
corrosion. This is especially true with the
artificially aged 7000 series alloys that are
susceptible to intergranular corrosion
when aged to peak strength.
HEAT TREATMENT PRECAUTIONS
Keep the number of heat treatments to a
minimum.
Clad materials must not be heat treated
more than three times because long
periods at high temperature causes the
copper atoms to move into the aluminium
coating, decreasing its corrosion
resistance and strength.
Do not rivet aluminium alloy sheet until at
least 24 hours has passed from the time
of solution heat treatment.
Failure to wait for this period can cause local
distortion at the rivet positions. Allow five
days to pass before putting the part into
service
Do not allow the metal to be overheated, or
heat it for too long a time. A large grain
size, causing brittleness, weakness and
roughness of the surface may result and
the part will have to be scrapped.
The maximum time between removal from
the heat treatment furnace and quenching
or Lag Time must be not more than 7
seconds.
Keep the number of heat treatments to a
minimum.
Clad materials must not be heat treated
more than three times because long
periods at high temperature causes the
copper atoms to move into the aluminium
coating, decreasing its corrosion
resistance and strength.
Do not rivet aluminium alloy sheet until at
least 24 hours has passed from the time
of solution heat treatment.
Failure to wait for this period can cause local
distortion at the rivet positions. Allow five
days to pass before putting the part into
service
Do not allow the metal to be overheated, or
heat it for too long a time. A large grain
size, causing brittleness, weakness and
roughness of the surface may result and
the part will have to be scrapped.
The maximum time between removal from
the heat treatment furnace and quenching
or Lag Time must be not more than 7
seconds.
HEAT TREATMENT INDICATION
•
•
•
As mentioned, not all aluminium alloys can
be heat treated. They are generally divided
into two groups termed:
Non-Heat Treatable - those that can be
softened but not hardened by heat
treatment.
Heat Treatable - those that can be
softened and hardened by heat treatment.
The first group rely on the work hardening
effects of manganese, silicon, magnesium
and iron when cold worked and so are
found in the 1000, 3000, 4000 and 5000
series.
If these Non-Heat Treatable alloys are heated
to their annealing temperature, around 350
- 400°C depending on the alloy, and
allowed to cool slowly they will be
softened to their annealed condition with
no temper.
•
•
•
As mentioned, not all aluminium alloys can
be heat treated. They are generally divided
into two groups termed:
Non-Heat Treatable - those that can be
softened but not hardened by heat
treatment.
Heat Treatable - those that can be
softened and hardened by heat treatment.
The first group rely on the work hardening
effects of manganese, silicon, magnesium
and iron when cold worked and so are
found in the 1000, 3000, 4000 and 5000
series.
If these Non-Heat Treatable alloys are heated
to their annealing temperature, around 350
- 400°C depending on the alloy, and
allowed to cool slowly they will be
softened to their annealed condition with
no temper.
IDENTIFICATION MARKINGS
Aluminium alloy sheet must be marked with
letters and numbers ink stamped at one
corner by the manufacturer, but it is
common practice to repeat these marks at
regular interval all over the sheet.
These identification symbols should include a
specification number, the alloy number
with temper designation, and the
thickness of the material in thousandths of
an inch (the thickness British material is
graded by Standard Wire Gauge - SWG).
On some material red markings are used to
indicate the material condition and further
processing required. These marks
disappear when the necessary heat
treatment is completed.
Aluminium alloy sheet must be marked with
letters and numbers ink stamped at one
corner by the manufacturer, but it is
common practice to repeat these marks at
regular interval all over the sheet.
These identification symbols should include a
specification number, the alloy number
with temper designation, and the
thickness of the material in thousandths of
an inch (the thickness British material is
graded by Standard Wire Gauge - SWG).
On some material red markings are used to
indicate the material condition and further
processing required. These marks
disappear when the necessary heat
treatment is completed.
CAST ALUMINIUM
Cast aluminium alloys often contain silicon,
which creates high fluidity and, thus, is
good for producing complex shapes. It also
reduces the coefficient of linear expansion,
so is often included in piston castings.
They are not used extensively on airframes
mainly due to their lack of strength, poor
fatigue characteristics and lack of
elasticity when compared to the wrought
aluminium alloys. The lack of elasticity is
particularly relevant, as the very nature of
an airframe structure requires the ability
to flex considerably without cracking.
Cast aluminium alloys often contain silicon,
which creates high fluidity and, thus, is
good for producing complex shapes. It also
reduces the coefficient of linear expansion,
so is often included in piston castings.
They are not used extensively on airframes
mainly due to their lack of strength, poor
fatigue characteristics and lack of
elasticity when compared to the wrought
aluminium alloys. The lack of elasticity is
particularly relevant, as the very nature of
an airframe structure requires the ability
to flex considerably without cracking.
MAGNESIUM AND MAGNESIUM ALLOYS
Magnesium is difficult to obtain from its ore,
and is now normally extracted from sea
water or deep well brine by electrolysis.
It is the lightest engineering metal in general
use, having a relative density of 1.7 and a
weight only 66% that of aluminium.
Silvery-white pure magnesium is a fairly weak
metal but alloying with small amounts of
aluminium, zinc, manganese and
zirconium will increase its strength.
Although weaker than aluminium alloys, their
lower densities often result in magnesium
alloys having a better strength to weight
ratio.
Magnesium is difficult to obtain from its ore,
and is now normally extracted from sea
water or deep well brine by electrolysis.
It is the lightest engineering metal in general
use, having a relative density of 1.7 and a
weight only 66% that of aluminium.
Silvery-white pure magnesium is a fairly weak
metal but alloying with small amounts of
aluminium, zinc, manganese and
zirconium will increase its strength.
Although weaker than aluminium alloys, their
lower densities often result in magnesium
alloys having a better strength to weight
ratio.
Without protection magnesium alloy corrodes
easily, but chemical surface treatments
and coating processes give it good
protection from corrosion by excluding
oxygen.
Most of the alloys can be annealed, solution
treated precipitation hardened in a similar
way to that used for aluminium alloys.
Magnesium alloys have been used to make
aircraft wheels, piston engine crankcases,
turbine engine compressor casings,
gearboxes, valve bodies etc. Magnesium
alloy sheet is used in the structure of
some aircraft and helicopters where
weight saving is particularly important.
American magnesium alloys are identified by
a series of letters and numbers. The first
letter or letters identify the main alloying
elements. The middle digits identify the
percentage of each of the identified
elements. The last letter and number
indicate the heat treatment of the alloy.
Example: AZ31A - T4
AZThe main alloying elements are
aluminium and zinc.
31This is 3% aluminium and 1% zinc. A
Indicates that the alloy is original.
T4The alloy has been solution heat treated
easily, but chemical surface treatments
and coating processes give it good
protection from corrosion by excluding
oxygen.
Most of the alloys can be annealed, solution
treated precipitation hardened in a similar
way to that used for aluminium alloys.
Magnesium alloys have been used to make
aircraft wheels, piston engine crankcases,
turbine engine compressor casings,
gearboxes, valve bodies etc. Magnesium
alloy sheet is used in the structure of
some aircraft and helicopters where
weight saving is particularly important.
American magnesium alloys are identified by
a series of letters and numbers. The first
letter or letters identify the main alloying
elements. The middle digits identify the
percentage of each of the identified
elements. The last letter and number
indicate the heat treatment of the alloy.
Example: AZ31A - T4
AZThe main alloying elements are
aluminium and zinc.
31This is 3% aluminium and 1% zinc. A
Indicates that the alloy is original.
T4The alloy has been solution heat treated
TITANIUM
Titanium is a greyish white metal having a
high strength to weight ratio. It has a
relative density of 4.5, making it 60%
heavier than aluminium, but twice as
strong, and 45% lighter than steel but
equal in strength. Titanium also falls
between Aluminium and Stainless Steel in
terms of elasticity, and elevated
temperature strength.Titanium has excellent corrosion resistance
properties due to the oxide film which
forms. It is not normally susceptible to
stress, fatigue, intergranular or galvanic
corrosion, pitting or localised attack. Under
certain circumstances it will burn in air, so
to prevent it's reaction with oxygen or
nitrogen it may be treated with chlorine
gas to form a coating of titanium dioxide.
Commercially pure titanium and some of its
alloys are non-heat treatable and can be
annealed but not hardened or
strengthened. These are usually hot
formed or rolled and work harden. When
suitably alloyed, heat treatable forms can
be produced which can be both annealed
and hardened. These are softer and more
ductile for cold working until hardened.The normal alloying elements include
aluminium, chromium, iron, manganese,
molybdenum and vanadium.
Titanium is a greyish white metal having a
high strength to weight ratio. It has a
relative density of 4.5, making it 60%
heavier than aluminium, but twice as
strong, and 45% lighter than steel but
equal in strength. Titanium also falls
between Aluminium and Stainless Steel in
terms of elasticity, and elevated
temperature strength.Titanium has excellent corrosion resistance
properties due to the oxide film which
forms. It is not normally susceptible to
stress, fatigue, intergranular or galvanic
corrosion, pitting or localised attack. Under
certain circumstances it will burn in air, so
to prevent it's reaction with oxygen or
nitrogen it may be treated with chlorine
gas to form a coating of titanium dioxide.
Commercially pure titanium and some of its
alloys are non-heat treatable and can be
annealed but not hardened or
strengthened. These are usually hot
formed or rolled and work harden. When
suitably alloyed, heat treatable forms can
be produced which can be both annealed
and hardened. These are softer and more
ductile for cold working until hardened.The normal alloying elements include
aluminium, chromium, iron, manganese,
molybdenum and vanadium.
Titanium and it's alloys are classed as A
(alpha), B (beta) and C (combined)
depending on their crystalline form:
A - is weldable, tough, strong both hot and
cold and resistant to oxidisation.
B - has excellent bend ductility, strong both
hot and cold but vulnerable to
contamination.
C - combined alpha and beta with
compromised performance, strong cold
and warm but weak hot, excellent
forgeability, good bendability, moderate
contamination resistance.
The melting point of titanium is 1668°C
It has low thermal conductivity
low coefficient of expansion.
(alpha), B (beta) and C (combined)
depending on their crystalline form:
A - is weldable, tough, strong both hot and
cold and resistant to oxidisation.
B - has excellent bend ductility, strong both
hot and cold but vulnerable to
contamination.
C - combined alpha and beta with
compromised performance, strong cold
and warm but weak hot, excellent
forgeability, good bendability, moderate
contamination resistance.
The melting point of titanium is 1668°C
It has low thermal conductivity
low coefficient of expansion.
TITANIUM SPECIFICATION
The American A-55 is an example of a
commercially pure titanium; it has a yield
strength of 55 to 80 ksi(kips* per square
inch) and is a general-purpose grade for
moderate to severe forming. It is
sometimes used for non-structural aircraft
parts and for all types of corrosion
resistant applications, such as tubing.Type A-70 titanium is closely related to type
A-55, but has a yield strength of 70 to 95
ksi. It is used where higher strength is
required, and it is specified for many
moderately stressed aircraft parts. For
many corrosion applications, it is used
interchangeably with type A-55. Type A-55
and type A-70 are weldable.* - kip is a US customary unit of force. It
equals 1000 pounds-force
One of the widely used titanium-base alloys is
C-110M. It is used for primary structural
members and aircraft skin, has 110 ksi
minimum yield strength, and contains 8
percent manganese.
Type A-110AT is a titanium alloy that contains
5 percent aluminium and 2.5 percent tin. It
also has a high minimum yield strength at
elevated temperatures with the excellent
welding characteristics inherent in alpha
type titanium alloys.
Titanium and its alloys are used to make
corrosion resistant, high strength bolts and
fasteners, compressor discs and blades
for gas turbine engines, fire walls, hot air
pipes, hydraulic pipes and structural parts
which require high strength or operate at
high temperatures. It is also used to skin
high performance aircraft where skin
friction prevents the use of aluminium.
The American A-55 is an example of a
commercially pure titanium; it has a yield
strength of 55 to 80 ksi(kips* per square
inch) and is a general-purpose grade for
moderate to severe forming. It is
sometimes used for non-structural aircraft
parts and for all types of corrosion
resistant applications, such as tubing.Type A-70 titanium is closely related to type
A-55, but has a yield strength of 70 to 95
ksi. It is used where higher strength is
required, and it is specified for many
moderately stressed aircraft parts. For
many corrosion applications, it is used
interchangeably with type A-55. Type A-55
and type A-70 are weldable.* - kip is a US customary unit of force. It
equals 1000 pounds-force
One of the widely used titanium-base alloys is
C-110M. It is used for primary structural
members and aircraft skin, has 110 ksi
minimum yield strength, and contains 8
percent manganese.
Type A-110AT is a titanium alloy that contains
5 percent aluminium and 2.5 percent tin. It
also has a high minimum yield strength at
elevated temperatures with the excellent
welding characteristics inherent in alpha
type titanium alloys.
Titanium and its alloys are used to make
corrosion resistant, high strength bolts and
fasteners, compressor discs and blades
for gas turbine engines, fire walls, hot air
pipes, hydraulic pipes and structural parts
which require high strength or operate at
high temperatures. It is also used to skin
high performance aircraft where skin
friction prevents the use of aluminium.
NICKEL AND ITS ALLOYS
•
•
•
Nickel is silvery white, takes on a high
polish and has good resistance to
corrosion.
It is hard, malleable, ductile, somewhat
ferro-magnetic, and a fair conductor of
heat and electricity with a melting point of
1455°C.
It belongs to the iron-cobalt group of
metals and is chiefly valuable for the alloys
it forms.
•
•
•
•
•
•
Electrical Resistance Alloys For Use at
High Temperatures:
These are usually nickel-chromium iron
alloys produced under trade names such
as 'Brightray' and 'Resistohm'. Their
important features are:
They do not oxidise at high temperatures.
They have a high melting point.
They have a high electrical resistance.
These alloys are used to make heater
elements for electric furnaces, soldering
irons etc. They are also used in
temperature sensing thermocouples.
Temperature sensing bulbs use nickel in
its pure form.
•
•
•
Nickel is silvery white, takes on a high
polish and has good resistance to
corrosion.
It is hard, malleable, ductile, somewhat
ferro-magnetic, and a fair conductor of
heat and electricity with a melting point of
1455°C.
It belongs to the iron-cobalt group of
metals and is chiefly valuable for the alloys
it forms.
•
•
•
•
•
•
Electrical Resistance Alloys For Use at
High Temperatures:
These are usually nickel-chromium iron
alloys produced under trade names such
as 'Brightray' and 'Resistohm'. Their
important features are:
They do not oxidise at high temperatures.
They have a high melting point.
They have a high electrical resistance.
These alloys are used to make heater
elements for electric furnaces, soldering
irons etc. They are also used in
temperature sensing thermocouples.
Temperature sensing bulbs use nickel in
its pure form.
•Low Expansion Alloys:
Most materials expand when they are heated
and contract again as they cool. Some
iron-nickel alloys, however, have very small
coefficients of thermal expansion, making
them very useful in many types of
precision equipment, used where
temperatures are always changing.
An alloy known as 'Invar' which contains 64%
iron and 36% nickel has a negligible
coefficient of expansion. It is used for bi-
metallic strip thermostats, precision
instruments and measuring equipment
and for cathode ray tube shadow masks.
High Temperature Corrosion Resistant Alloys:
These are sometimes known as Superalloys.
Among the first of these were the 'Nimonic'
series of alloys developed in the UK in the
early 1940's for gas turbine applications.
They are basically nickel-chromium alloys,
stiffened and strengthened by adding
small amounts of titanium, aluminium,
cobalt and molybdenum.
Development has continued and nimonic
alloys are still used in the latest engines.
Most materials expand when they are heated
and contract again as they cool. Some
iron-nickel alloys, however, have very small
coefficients of thermal expansion, making
them very useful in many types of
precision equipment, used where
temperatures are always changing.
An alloy known as 'Invar' which contains 64%
iron and 36% nickel has a negligible
coefficient of expansion. It is used for bi-
metallic strip thermostats, precision
instruments and measuring equipment
and for cathode ray tube shadow masks.
High Temperature Corrosion Resistant Alloys:
These are sometimes known as Superalloys.
Among the first of these were the 'Nimonic'
series of alloys developed in the UK in the
early 1940's for gas turbine applications.
They are basically nickel-chromium alloys,
stiffened and strengthened by adding
small amounts of titanium, aluminium,
cobalt and molybdenum.
Development has continued and nimonic
alloys are still used in the latest engines.
Another well known family of high
temperature alloys is the “Inconel‟ group
developed in the U.S.
Inconel 600 contains 76% nickel, 15%
chromium and 8% iron with small amounts
of cobalt, manganese, carbon etc.
Others within the family contain Zirconium,
Molybdenum, aluminium and various other
elements to obtain the desired
characteristics.
Their appearance and performance are
similar to stainless steel at low
temperatures and they remain very tough
at high temperatures and do not oxidise
very much because of the protective film
of chromium oxide which forms on the
surface.
•
•
Other alloys in this type are Incoloy, Udimar,
Udimet, Nilo, Waspaloy and Hastasloy.
They are used throughout gas turbine
engines where high strength at high
temperatures and resistance to oxidation
and creep are required. They are also used
structurally where high strength, corrosion
resistant components and fasteners are
required.MONEL METAL:
This is an alloy containing 68% Nickel, 29%
Copper, 1.5% Iron and 1.5% Manganese. It
has good resistance to corrosion. It is
malleable and used to make rivets.
temperature alloys is the “Inconel‟ group
developed in the U.S.
Inconel 600 contains 76% nickel, 15%
chromium and 8% iron with small amounts
of cobalt, manganese, carbon etc.
Others within the family contain Zirconium,
Molybdenum, aluminium and various other
elements to obtain the desired
characteristics.
Their appearance and performance are
similar to stainless steel at low
temperatures and they remain very tough
at high temperatures and do not oxidise
very much because of the protective film
of chromium oxide which forms on the
surface.
•
•
Other alloys in this type are Incoloy, Udimar,
Udimet, Nilo, Waspaloy and Hastasloy.
They are used throughout gas turbine
engines where high strength at high
temperatures and resistance to oxidation
and creep are required. They are also used
structurally where high strength, corrosion
resistant components and fasteners are
required.MONEL METAL:
This is an alloy containing 68% Nickel, 29%
Copper, 1.5% Iron and 1.5% Manganese. It
has good resistance to corrosion. It is
malleable and used to make rivets.
Copper and its Alloys
Copper is a good conductor of heat and
electricity and is reddish brown in colour.
When cut, it forms a greenish oxide layer
(verdigris) which protects it from further
corrosion. It is very malleable and ductile
and can be shaped by rolling, drawing,
forging and pressing. Copper is used to
make electrical cables and parts for
electrical equipment.Copper is one of the few metals which is
mechanically strong enough to be used in
its (nearly) pure form. It is also valuable
both as a constituent and as a base of
alloys.
Copper is a good conductor of heat and
electricity and is reddish brown in colour.
When cut, it forms a greenish oxide layer
(verdigris) which protects it from further
corrosion. It is very malleable and ductile
and can be shaped by rolling, drawing,
forging and pressing. Copper is used to
make electrical cables and parts for
electrical equipment.Copper is one of the few metals which is
mechanically strong enough to be used in
its (nearly) pure form. It is also valuable
both as a constituent and as a base of
alloys.
TUNGUM
Tungum is an alloy containing 81% to 86% copper and small amounts of
nickel, silicon, aluminium and zinc. It is highly resistant to fatigue and
corrosion, is strong and ductile and was used to make hydraulic and other
pipelines. However it was found to become brittle over extended time
scales and is no longer used on aircraft.
Tungum is an alloy containing 81% to 86% copper and small amounts of
nickel, silicon, aluminium and zinc. It is highly resistant to fatigue and
corrosion, is strong and ductile and was used to make hydraulic and other
pipelines. However it was found to become brittle over extended time
scales and is no longer used on aircraft.
BRASS
Brasses are copper based alloys containing
up to 45% zinc and sometimes small
amounts of other metals such as tin, lead,
aluminium, manganese and iron, these
additions increase the tensile strength and
resistance to corrosion.
Some brasses are very ductile and their
sheets can be pressed and drawn into
deep sections. Others are more suited to
hot working and stamping. All are readily
machinable. Brass is used in the
manufacture of instrument mechanisms,
bellows assemblies and pitot heads.
Brasses are copper based alloys containing
up to 45% zinc and sometimes small
amounts of other metals such as tin, lead,
aluminium, manganese and iron, these
additions increase the tensile strength and
resistance to corrosion.
Some brasses are very ductile and their
sheets can be pressed and drawn into
deep sections. Others are more suited to
hot working and stamping. All are readily
machinable. Brass is used in the
manufacture of instrument mechanisms,
bellows assemblies and pitot heads.
BRONZE
Bronzes are copper based alloys containing
up to 25% tin, sometimes with smaller
amounts of phosphorus, zinc or lead. Low
tin bronzes are used for springs and
instrument parts, tubes and pipes as they
have good elastic properties and are
corrosion resistant. High tin bronzes are
often cast and are used in bearings and
bushes which are subjected to heavy loads.
There are other copper alloys that contain
practically no tin and yet are still referred
to as “bronzes‟. For instance „Manganese
Bronze‟, so called because of its
manganese content, is 55% copper, 40%
zinc 3.5% manganese, 1% tin (technically a
Brass rather than Bronze) while Phosphor
and Silicon bronzes also contain practically
no tin at all. Wrought aluminium bronzes
are almost as strong as medium-carbon
steel while cast aluminium bronzes are
found in bearings and pump parts.
Bronzes are copper based alloys containing
up to 25% tin, sometimes with smaller
amounts of phosphorus, zinc or lead. Low
tin bronzes are used for springs and
instrument parts, tubes and pipes as they
have good elastic properties and are
corrosion resistant. High tin bronzes are
often cast and are used in bearings and
bushes which are subjected to heavy loads.
There are other copper alloys that contain
practically no tin and yet are still referred
to as “bronzes‟. For instance „Manganese
Bronze‟, so called because of its
manganese content, is 55% copper, 40%
zinc 3.5% manganese, 1% tin (technically a
Brass rather than Bronze) while Phosphor
and Silicon bronzes also contain practically
no tin at all. Wrought aluminium bronzes
are almost as strong as medium-carbon
steel while cast aluminium bronzes are
found in bearings and pump parts.
One of the most important of the bronzes to
aviation is Beryllium Bronze. This contains
97% copper, 2% beryllium and small
amounts of nickel to increase its strength.
Once it has been heat-treated, beryllium
bronze is very strong (300-400 Brinell) and
is used for diaphragms, precision bearings
and high performance bushings, ball
bearing cages and spring washers.
The Sintering process involves the
compaction of powdered metal, or metals,
in a mould under pressure of up to 50 tons
per square inch. The item is removed from
the mould, heated in a furnace to a
temperature below the melting point and
held there until the particles become
chemically bonded. The resultant part
remains porous. Sintered Bronzes are
often used to make small oil retaining
bearings and filters.
aviation is Beryllium Bronze. This contains
97% copper, 2% beryllium and small
amounts of nickel to increase its strength.
Once it has been heat-treated, beryllium
bronze is very strong (300-400 Brinell) and
is used for diaphragms, precision bearings
and high performance bushings, ball
bearing cages and spring washers.
The Sintering process involves the
compaction of powdered metal, or metals,
in a mould under pressure of up to 50 tons
per square inch. The item is removed from
the mould, heated in a furnace to a
temperature below the melting point and
held there until the particles become
chemically bonded. The resultant part
remains porous. Sintered Bronzes are
often used to make small oil retaining
bearings and filters.
LEAD AND ITS ALLOYS
Lead is bright and lustrous when freshly cut,
but soon oxidises to a dull grey. It is very
heavy and has a relative density 11.3. It is
soft and malleable, resistant to corrosion
and has a low melting point, 327ºC. It also
has self lubricating properties and is used
in some bushing alloys.
Lead is a major constituent of soft solder. It
has been used to make flying control
surface mass balance weights. It gives
protection from X-rays and is used to
make containers for radio-active isotopes,
used during certain non-destructive tests
on aircraft engines and airframes.
•WHITE BEARING MATERIALS:
White bearing metals used in piston engines
are either tin base or lead base. Tin base
bearing metals are known as Babbitt
metals and contain between 3.5% and 15%
Antimony. e.g. 7% antimony, 90% tin and
3% copper. They are generally heavy duty
bearing metals
The lead based White Metals are intended for
lower duty since they can withstand only
limited pressures. They also contain tin
and antimony e.g. 13% antimony, 12% tin,
0.75% copper and lead the remainder..
Lead is bright and lustrous when freshly cut,
but soon oxidises to a dull grey. It is very
heavy and has a relative density 11.3. It is
soft and malleable, resistant to corrosion
and has a low melting point, 327ºC. It also
has self lubricating properties and is used
in some bushing alloys.
Lead is a major constituent of soft solder. It
has been used to make flying control
surface mass balance weights. It gives
protection from X-rays and is used to
make containers for radio-active isotopes,
used during certain non-destructive tests
on aircraft engines and airframes.
•WHITE BEARING MATERIALS:
White bearing metals used in piston engines
are either tin base or lead base. Tin base
bearing metals are known as Babbitt
metals and contain between 3.5% and 15%
Antimony. e.g. 7% antimony, 90% tin and
3% copper. They are generally heavy duty
bearing metals
The lead based White Metals are intended for
lower duty since they can withstand only
limited pressures. They also contain tin
and antimony e.g. 13% antimony, 12% tin,
0.75% copper and lead the remainder..
Miscellaneous Metals
•Depleted Uranium:
Depleted Uranium (DU) is a by-product of the
nuclear enrichment process and is 1.7
times as dense as lead. Because of its
weight it has, in the past, been used to
produce balance weights for aircraft flight
control surfaces.
Uranium and its compounds are, however,
highly toxic, both from a chemical and
radiological standpoint. It is important that
this material is handled carefully and
maintenance manual instructions
observed.
•
•
Damaged coatings may be repaired if no
corrosion is evident. Corroded weights
must be removed, packaged as described
in the manual and returned to the
originator. Under no circumstances may
DU weights be cut, machined or
mechanically cleaned. Adequate
protection must be worn when handling
corroded or damaged DU.Tungsten:
Tungsten is a hard, dense, corrosion
resistant metal which is used in light bulb
filaments and as an alloying element in
steels. Tungsten based alloy has also
largely replaced depleted uranium as the
material for balance weights. As it is less
dense than DU the weights are larger.
•Depleted Uranium:
Depleted Uranium (DU) is a by-product of the
nuclear enrichment process and is 1.7
times as dense as lead. Because of its
weight it has, in the past, been used to
produce balance weights for aircraft flight
control surfaces.
Uranium and its compounds are, however,
highly toxic, both from a chemical and
radiological standpoint. It is important that
this material is handled carefully and
maintenance manual instructions
observed.
•
•
Damaged coatings may be repaired if no
corrosion is evident. Corroded weights
must be removed, packaged as described
in the manual and returned to the
originator. Under no circumstances may
DU weights be cut, machined or
mechanically cleaned. Adequate
protection must be worn when handling
corroded or damaged DU.Tungsten:
Tungsten is a hard, dense, corrosion
resistant metal which is used in light bulb
filaments and as an alloying element in
steels. Tungsten based alloy has also
largely replaced depleted uranium as the
material for balance weights. As it is less
dense than DU the weights are larger.
Cadmium: Cadmium is a bluish-white metal
which is used as a corrosion protective
sacrificial coating on steel parts. Because
cadmium is less electrochemically active
than zinc or aluminium, it is frequently
used on high- strength steel parts that
might be embrittled by more active,
sacrificial corrosion reactions and that
contact aluminium parts. It is commonly
used on steel fasteners and their mating
parts (nuts washers etc.) and followed by
chromate passivation which gives them a
golden yellow colour.
If used in high temperature environments,
however, the cadmium has a tendency to
cause Liquid Metal Embrittlement where it
melts and diffuses in to the underlaying
grain structure, weakening the steel.
Cadmium plated parts should, therefore,
never be used on engine hot sections. It
also reacts with titanium and the two
should not be allowed to come into
contact..
Pure cadmium and solutions of its
compounds are toxic by ingestion.
which is used as a corrosion protective
sacrificial coating on steel parts. Because
cadmium is less electrochemically active
than zinc or aluminium, it is frequently
used on high- strength steel parts that
might be embrittled by more active,
sacrificial corrosion reactions and that
contact aluminium parts. It is commonly
used on steel fasteners and their mating
parts (nuts washers etc.) and followed by
chromate passivation which gives them a
golden yellow colour.
If used in high temperature environments,
however, the cadmium has a tendency to
cause Liquid Metal Embrittlement where it
melts and diffuses in to the underlaying
grain structure, weakening the steel.
Cadmium plated parts should, therefore,
never be used on engine hot sections. It
also reacts with titanium and the two
should not be allowed to come into
contact..
Pure cadmium and solutions of its
compounds are toxic by ingestion.
Chromium: Apart from being used in high
performance steels, chromium is
important as a plating material. In aviation
it is used to give a hard, smooth, protective
coating rather than just a decorative finish.
Hard- chromium (as opposed to 'Bright
Chrome') plating is used for improving
sliding and sealing properties, preventing
wear and, in thick layers, corrosion. It is
typically used for hydraulic cylinders and
rams, and undercarriage oleo legs.
Thickness varies from 10 to 1000 micron.
Chromium compounds are toxic and should
be handled with proper safeguards.
performance steels, chromium is
important as a plating material. In aviation
it is used to give a hard, smooth, protective
coating rather than just a decorative finish.
Hard- chromium (as opposed to 'Bright
Chrome') plating is used for improving
sliding and sealing properties, preventing
wear and, in thick layers, corrosion. It is
typically used for hydraulic cylinders and
rams, and undercarriage oleo legs.
Thickness varies from 10 to 1000 micron.
Chromium compounds are toxic and should
be handled with proper safeguards.
Metal Fatigue
•General :
Fatigue is, however, closely associated with corrosion. Each can accelerate the
development of the other and together they pose a serious threat of catastrophic failure.
Briefly, fatigue is the phenomena where by a component which is subjected to repeated
cyclic loading will eventually fail at a stress level far lower than its ultimate failure load.
The number of cycles required to cause this fatigue failure is dependent on the
magnitude of the load applied. It can be plotted using SN graph (Stress vs no. of cycles
to failure)
•General :
Fatigue is, however, closely associated with corrosion. Each can accelerate the
development of the other and together they pose a serious threat of catastrophic failure.
Briefly, fatigue is the phenomena where by a component which is subjected to repeated
cyclic loading will eventually fail at a stress level far lower than its ultimate failure load.
The number of cycles required to cause this fatigue failure is dependent on the
magnitude of the load applied. It can be plotted using SN graph (Stress vs no. of cycles
to failure)
Fatigue failure is caused by microscopic flaws
or faults in the metal structure. These may
be inclusion particles, voids, cracks,
intergranular corrosion, scratches,
blemishes, pits or micro- cracks. The
repeated stress reversals cause these
faults to enlarge, concentrating stress on
the 'good' material and reducing the load
carrying capacity of the component until
eventual failure.On an aircraft, the fatigue loads will vary
considerably depending on the nature of
its operation, the environment it operates
in and it's handling on the ground and in
the air.
Typical loads which may be encountered are:
Atmospheric gusts (winds that vary
randomly in space and time)
Manoeuvres (a planned and controlled
movement or operation by the armed
forces)
Taxiing (move slowly along the ground
before take-off or after landing)
Ground handling (aircraft ground handling
defines the servicing of an aircraft while it
is on the ground)
Landing impact (The plane had to make a
forced landing because one of the engines
cut out.)
Ground-air-ground cycles. (involving a
weapon that is shot from an aircraft at a
place on the ground)
or faults in the metal structure. These may
be inclusion particles, voids, cracks,
intergranular corrosion, scratches,
blemishes, pits or micro- cracks. The
repeated stress reversals cause these
faults to enlarge, concentrating stress on
the 'good' material and reducing the load
carrying capacity of the component until
eventual failure.On an aircraft, the fatigue loads will vary
considerably depending on the nature of
its operation, the environment it operates
in and it's handling on the ground and in
the air.
Typical loads which may be encountered are:
Atmospheric gusts (winds that vary
randomly in space and time)
Manoeuvres (a planned and controlled
movement or operation by the armed
forces)
Taxiing (move slowly along the ground
before take-off or after landing)
Ground handling (aircraft ground handling
defines the servicing of an aircraft while it
is on the ground)
Landing impact (The plane had to make a
forced landing because one of the engines
cut out.)
Ground-air-ground cycles. (involving a
weapon that is shot from an aircraft at a
place on the ground)
Fatigue Life and Safety Margin
With growing experience, manufacturers are
now better able to predict structural
fatigue and design and build airframes
with better fatigue lives and safety
margins.
Methods used include:
the elimination of stress risers by careful
design, e.g. position of holes etc.
shot peening of surfaces of highly stressed
components
cold working of holes in critical areas
use of modern fasteners
high degrees of surface finish
development of maintenance programmes
to ensure that faults are detected and
repaired.
In the maintenance arena it is important that
all inspections and repairs are carried out
to the highest standards to detect the
onset of fatigue cracks and prevent their
propagation. Unusual events such as
heavy or overweight landings and flight
through turbulence must be thoroughly
investigated in accordance with the
manufacturer‟s instructions.
With growing experience, manufacturers are
now better able to predict structural
fatigue and design and build airframes
with better fatigue lives and safety
margins.
Methods used include:
the elimination of stress risers by careful
design, e.g. position of holes etc.
shot peening of surfaces of highly stressed
components
cold working of holes in critical areas
use of modern fasteners
high degrees of surface finish
development of maintenance programmes
to ensure that faults are detected and
repaired.
In the maintenance arena it is important that
all inspections and repairs are carried out
to the highest standards to detect the
onset of fatigue cracks and prevent their
propagation. Unusual events such as
heavy or overweight landings and flight
through turbulence must be thoroughly
investigated in accordance with the
manufacturer‟s instructions.
Shot Peening
This compressive layer is often produced by
shot peening where small balls of known
diameter are blasted with predetermined
force against the surfaces to be protected.
The balls used may be steel shot or glass
or ceramic beads, depending on the
material being treated. Components are
treated in sealed cabinets or chambers
while areas in-situ on the aircraft are
treated using portable Vacu-blast type
equipment similar to that used for
corrosion removal.
The exposure time is determined by first
peening a spring steel test piece or 'Almen
strip' in a special holder for a set duration.
This is then inspected for coverage
(density of impacts) and intensity (by
measuring the deflection or curvature of
the strip). The air pressure and time are
altered accordingly and a new Almen strip
is used until the correct coverage (100%)
and intensity is achieved.Each component to be treated is given an
Almen number dependant on its material
and coverage requirement. The exposure
time determined from the test strips is
then factored by the Almen number,
coverage requirements and surface area
to give the total treatment time.
This compressive layer is often produced by
shot peening where small balls of known
diameter are blasted with predetermined
force against the surfaces to be protected.
The balls used may be steel shot or glass
or ceramic beads, depending on the
material being treated. Components are
treated in sealed cabinets or chambers
while areas in-situ on the aircraft are
treated using portable Vacu-blast type
equipment similar to that used for
corrosion removal.
The exposure time is determined by first
peening a spring steel test piece or 'Almen
strip' in a special holder for a set duration.
This is then inspected for coverage
(density of impacts) and intensity (by
measuring the deflection or curvature of
the strip). The air pressure and time are
altered accordingly and a new Almen strip
is used until the correct coverage (100%)
and intensity is achieved.Each component to be treated is given an
Almen number dependant on its material
and coverage requirement. The exposure
time determined from the test strips is
then factored by the Almen number,
coverage requirements and surface area
to give the total treatment time.
SHOT PEENING
SHOT PEENING OPERATION
Rotopeening
Small inaccessible areas and components in-
situ (in the original place) can also be
treated by Rotopeening. Several tungsten
carbide balls are held captive in a flexible
strip or 'flap wheel' which is mounted in a
mandrel. This in turn is held in a high
speed windy drill. Testing is similar to that
for shot peening but intensity is governed
by drill speed which must be kept constant.
Small inaccessible areas and components in-
situ (in the original place) can also be
treated by Rotopeening. Several tungsten
carbide balls are held captive in a flexible
strip or 'flap wheel' which is mounted in a
mandrel. This in turn is held in a high
speed windy drill. Testing is similar to that
for shot peening but intensity is governed
by drill speed which must be kept constant.
Cold Working
Compressive stress can be induced around
fastener holes by several methods. 'Cold
working' or 'cold expansion' is the most
commonly used in critical areas. In this
process the hole is drilled, reamed and
deburred. A mandrel mounted in a
powered puller tool and a lubricated sleeve
are then inserted into the hole. With the
sleeve seated the mandrel is drawn
through it, the interference causing the
hole to expand and the material around it
to be compressed. The fatigue life of a
cold worked hole is between 3 and 10
times better than for a plain drilled hole.
A similar effect to cold working can be
achieved by using interference fit
fasteners such as 'Hi- loks'. 'Hi-Tigue'
fasteners have a radiused lead-in at the
thread end of the shank which broaches
the hole as the fastener is driven home.
'Taperlok' fasteners also compress the
surrounding material as the fastener is
drawn into the tapered hole. The effects of
these fasteners are, however, less
controllable than the cold working process.Before attempting to perform any of these
operation you should be fully conversant
with the process specification and all
equipment to be used. Additional training
and authorisation may be required.
Compressive stress can be induced around
fastener holes by several methods. 'Cold
working' or 'cold expansion' is the most
commonly used in critical areas. In this
process the hole is drilled, reamed and
deburred. A mandrel mounted in a
powered puller tool and a lubricated sleeve
are then inserted into the hole. With the
sleeve seated the mandrel is drawn
through it, the interference causing the
hole to expand and the material around it
to be compressed. The fatigue life of a
cold worked hole is between 3 and 10
times better than for a plain drilled hole.
A similar effect to cold working can be
achieved by using interference fit
fasteners such as 'Hi- loks'. 'Hi-Tigue'
fasteners have a radiused lead-in at the
thread end of the shank which broaches
the hole as the fastener is driven home.
'Taperlok' fasteners also compress the
surrounding material as the fastener is
drawn into the tapered hole. The effects of
these fasteners are, however, less
controllable than the cold working process.Before attempting to perform any of these
operation you should be fully conversant
with the process specification and all
equipment to be used. Additional training
and authorisation may be required.
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