NON FERROUS MATERIALS Notes for eng.pptx

NON FERROUS

1. MODULE 2 NON FERROUS MATERIALS IN AIRCRAFT CONSTRUCTION

2. Aluminum alloys form the major airframe material and are used in abundance in the general structure of aircraft on account of their low specific gravity, reasonable strength case of fabrication and they are only 1/3rd as heavy as steel. Aluminium alloys are classified into two types: 1. Wrought alloys 2. Cast alloys Aluminium is found in most clays, soils, and rocks, but the principal commercial source is the ore bauxite. Bauxite is largely aluminium oxide mixed with impurities. These impurities are removed by a chemical process called Bayer's process, leaving the pure aluminum oxide, alumina.

3. An electrolytic process is used to obtain aluminum from the oxide. The metallic aluminum obtained by the electrolytic process is cast into pig form. These pigs are later remelted to form the commercial ingot used in rolling, forging, extruding, and other fabricating processes. By the addition of other constituents during the remelting operations, many alloys of aluminium are obtained with varying properties.

4. A.A . Number 1XXX Aluminum 99.00% (PURE) 2XXX Copper is the main alloying element 3XXX Manganese i s the m a in alloying e l ement 4XXX Silicon is the main alloying element 5XXX Magnesium i s the main alloying e l ement 6XXX Magnesium and silicon are the main alloyin g elements 7XXX Zinc is the main alloying element 8XXX Special element a lloys 9XXX Unused series Ex: Al6061: 6-alloy group; 0- impurity: 61- 99.61 (purity of Al used for composition) NOMENCLATURE: The Aluminum Association has published a new alloy designation system for aluminum alloys. The new system has all the wrought aluminum alloys designated by a four-digit system. The First digit indicates the principal alloying elements, the second digit is the modification(variation) of original material or impurity limits and the last two digits represents the aluminium alloy or aluminium purity.

5. TEMPERING: Tempering is a process of improving the characteristics of a metal and decreasing the hardness of the metal by heating it to a temperature below critical temperature. The reduction in hardness is usually accompanied by an increased in ductility, thereby decreasing the brittleness. Annealing and Normalizing are the primary processes, whereas the tempering is a secondary process which is done after the primary process. The wrought alloys can be manufactured in a number of different tempers. The temper designation consists of the letter 0 , F, H or T followed by a number.

6. The temper designation O indicates annealed wrought material and F indicates the as fabricated condition in which no effort has been made to control the mechanical properties. The temper designation H is applied to those alloys that are strain-hardened by cold work. The commonly used alloys of this type are 3003-H 12, 3003-H 14, 3003-H16, 3003- Hl8, and 5052-H32, 5052-H34, 5052-H36 and 5052-H38. The first digit after H represents temper has been produced by merely cold-working the material. The second digit after H represents the relative hardness and tensile strength.

7. The basic temper d esignations f or the h ea l-treatable a ll oys are as follows: T2-Annealed cas tin gs T 3- Solution heat-treated and th en co ld- worked T4-Solution heal-treated T S-Ar tifi c iall y aged only T6-Solution heal-treated and th en artificiall y aged TI-Solut i on heat-treated and then stabi li zed TS-Solution heat-tr eated, co ld- wor ked , and then artificially aged T9-Solulion heat-treated , artificially aged. a nd then co l d-worked

8. CLASSIFICATION OF WROUGHT ALLOYS: The wrought aluminum alloys may be broadly c lassified und e r o ne of two gro up s as ei ther strain-hardened alloys or heat-treatable alloys. In th e first group the physical properties are improved so l e ly by cold working , whereas in th e h ea t - treatable group th e properties are improv e d by h eat tr ea tm e nt. Further impro vement of the h ea t treated group is obtainable by co ld working s li ght ly after heat treatment. The s train - hardened alloys do n o t r espo nd to a n y heat treatment ot h er than a soften in g, annealing tr eatment . CORROSION: There are four types of corrosion: 1. Environmental corrosion 2. Sea water corrosion 3. Pitting 4. Inter-crystalline corrosion

9. Pure aluminum 1100 is very resistant to atmosp heric co rrosion but when alloying elements are added, th e co rro sio n resistance is de creased . 5052 is more resi stan t to sa lt -water corrosion than 1100 but not atmospher ic corrosion . It is customary in Naval ai rcraft work to pro t ect all alumin um alloys with a coating of paint. A good protective coating i s particularl y imp o rtant w hen th e ai rplan e w ill b e s u bjected to seve re co r rosive conditio n s , as i n th e c a se o f a sea plan e. An other t y pe of corro s i on of alumin um alloys is th e pittin g of th e s urfa ce , w hich i s a n a l og o u s t o th e ru s tin g o f i ro n . T hi s eating awa y o f the s urface i s accelera t ed i n th e presence of m oi s tur e, part i c ul arly s alt water.

10. Thi s t ype of co r ros i o n occ ur s mo s t often i n parts of th e s tru c tur e t h a t a r e poorl y ve ntil a t ed , and in in access ibl e co rn ers of in ternal join t s. Int e r-c ry s talline corrosion is a much m o r e se ri o us t ype o f corrosion , s ince it grea tl y r ed u ces th e s trength a nd de s troy s the d u c tilit y o f the metal. Thi s type of co rro s i o n is a p pare ntl y limit ed t o a luminum a ll oys co ntaining co pper , s u c h a s 20 17 and 2024 . The resista n ce of th ese m a terial s to th is typ e o f corros i o n i s l owere d by i n correct h eat treatment or b y s l ow o r delayed qu e nchi ng.

11. EXTRUSIONS: In aircraft construction channels, ang l es, T-sections, Z-sections, and many other specia l structural shapes are required. These shapes are a ll obta in ab l e in aluminum alloy by an extruding process. In this process a cyli nd er of a luminum a llo y is heated between 750° and 850°F. and is th e n forced by a hydraulic ram through an apert u re in a die. The aperture is th e shape desired for the cross-section of the finished extrusion. Extruded material has performed satisfacto ril y but it does not have so fine a grain, nor is it so homogeneou s as rolled or forged material

12. FORGINGS: Aluminum alloys may be forged to clo se limit s to provide light , s trong fitting s, o r o th er st ru c tural parts . The se forgings have a uniform , st ru c tur e and are free fr o m blo w h o l es, hard-sp o t s, or cavities. Onl y a few th o u sa nds o f an in c h need be allowed for finish-machining. In forging, the metal i s heated to th e p r o p er fo r g in g t e mp era tur e fo r t h e p ar t a n d t h en h a m mere d , pressed, d rop-forge d , o r u p se t t o s h ape. Pr esse d fo r gi n gs have a fi n e f i ni s h a nd c an b e h e l d to cl ose t o l e ran ces . Th e a luminum a ll oys c omm o nl y u sed fo r a ir c raft fo r g in gs are 20 1 4, 2 01 7, 20 2 5 , 4 032, 6053, 61 5 1 , a nd 707 5 . Because of their superior resistance to corrosion 2014 and 7075 are used in airplane structures. For engine parts 6151 and 2025 are used because the sections are heavy and frequently oily. Propellers made from -2025 have performed satisfactorily in service for years. Press (6053) forgings are ideal for tank flanges which are welded in place.

13. S P O T - WEL D I NG A L UMI NU M ALL O Y S: E l ectr i c s p o t a nd seam we l d in g of a luminum a ll oys h as bee n ge n e rall y a d o pt ed fo r jo ini ng ' no n s t ruc tu ra l an d semi st ru c tu ra l pa rt s. Spo t w el d in g h as di s pl ace d riv e tin g in m a n y app li ca ti ons, du e t o it s spee d , l owe r cos t , and e liminat io n of pro j ec t i n g rive t h ea d s . It h as a lr ea d y been u se d s u ccessf ull y in welding fuel t anks. Other common uses are ' the attachment of stiffe n ers to cowling, st rin gers to fuselage and wing skins, and in the assemb l y of brackets and she lve s. Spot we ldin g is genera lly used in th e fabrication of primary structura l parts of airplanes. HEAT TREATMENT: There are two types of heat treatment applicable to aluminum alloys. One is called solution heat treatment, and the other is known as precipitation heat treatment. Some alloys, such as 2017 and 2024 develop their full properties as a result of solution heat treatment followed by about 4 days aging at room temperature. Other alloys, such as 2014 and 7075, require both heat treatments.

14. SOLUTION HEAT TREATMENT

15. The most important point in connection with the furnace selected is that it must maintain an even temperature throughout its interior. In the electric air furnace provision should be incorporated for circulating the air. The length of time that material must be soaked at the proper temperature depends upon the nature of the material, the prior heat treatment of the thick- ness of the material, and the type of heat-treating equipment. After soaking, the work is removed from the bath or furnace and quickly quenched in cold water. It is extremely important that not more than a few seconds elapse before quenching the hot material, or the resistance and strength will be seriously affected.

16. PRECIPITATION HEAT TREATMENT Precipitation heat treatment consists of aging material previously subjected to solution heat treatment by holding it at an elevated temperature for quite a long period of time. During this treatment a portion of the alloying constituents in solid solution precipitate out. This precipitation occurs at ordinary room temperatures in the case of 2017 and 2024 material. The precipitate is in the form of extremely fine particles which, due to their "keying" action, greatly increase the strength. The "natural aging" of2017 and 2024 material at room temperatures is 90% to 98% complete after 24 hours, and fully complete after four days. Alloy 2024 develops greater strength than 2017 immediately after quenching, ages more rapidly, and is considerably less workable. Precipitation heat treatment of aluminum alloys consists ·in heating the material for from 8 to 24 hours at a temperature around 300°F. In practice an oven heated by steam coils or an electric furnace is used for heating.

17. ALUMINUM-ALLOY CASTINGS Aluminum-alloy castings are frequently used in aircraft construction . As the case with all castings, their mechanical properties, shock resistance, and ductility are inferior to those obtainable with wrought alloys. There are three ways of casting aluminum alloys: (1) Sand Casting, (2) Permanent Mold Casting, and (3) Die Casting. Sand casting is the most common and is used for complicated shapes or where only a few parts are required. Permanent-mold casting is similar to sand casting, but a metal mold is used which permits the making of many parts with better accuracy than sand casting. Die casting is used when many small parts must be made and held to close tolerances.

18. SAND CASTING Sand casting of aluminum alloys is the method most frequently resorted to in obtaining castings for aircraft construction The quantity of castings required is usually fairly small and would not warrant the manufacture of a permanent metal mold or die. The wooden · patterns used for sand casting will stand under the manufacture of several hundred castings unless they are abused or the casting is of unusual shape. Patterns made of white metal are sometimes substituted for wood . It is advisable to let the casting manufacturer also make the pattern from the designer's blueprint.

19. When this is done there can be no question about obtaining the proper shrinkage and machining allowance. The shrinkage allowance for aluminum-alloy sand castings is 5/32 inch per foot. If a machine finish is desired, 1/i6 inch should be allowed for machining, particularly on the upper surface of the casting where the impurities collect. Applications Alloy No. 43-It has been used for carburetors, hot-air scoops, fuel-line fittings, and fuel- and oil-tank flanges. Alloy No. 355-T6-Its leakproof and heat-resisting qualities have been utilized in the manufacture of water-cooled cylinder heads for engines.

20. PERMANENT-MOLD CASTING Perman e nt-mold casting i s similar to sa nd casting except for the use of a metal mold . The manufacture of this mold is re l atively expensive and i s only justified when a large number of castings are required. Castings with complicated cores cannot be manufactured in metal molds. Sometimes cores are fabricated of sand in the metal mold. This process is called se mi-permanent mold casti n g. It utili z e s the advantages of both s and and mold c asting .

21. In · mold casting the molt e n meta! is fed into the mold by grav ity . The mold is hot but chills the molten metal as it comes in contact with it. Chilling · resu lt s in more rapid solidifica t ion and a finer grain. This finer grain makes perman en t -mo ld cas tin gs more s u scep tible to heat treatment , and improves their corros i o n re s i s t ance a nd physical properties . Applications: All o y s Nos . 122 , A 1 3 2 , and 142 have been u se d for engine pistons . Alloy No. 356 has excellent cast ing qualities, good corros i o n resistance a nd good mechanical properties.