Modification of Surface Properties of AA7075 ­­ by Friction Stir Processing

Modification of Surface Properties of AA7075 ­­ by Friction Stir Processing

1. Modification of Surface Properties of AA7075 ­­ by Friction Stir Processing Koona Bhavani 1[0000-0002-8100-4163] , V.S.N. Venkata Ramana 2[0000-0003-3725-5448] , Rahul 3[0000-0001-5343-2657] , Ch. Lakshmi Kanth 4[0000-0002-5248-556X] , K. Sri Ram Vikas 5[0000-0002-4322-8465] , Ch. Kishore Reddy 6[0000-0002-4584-7913] 1,2 Department of Mechanical Engineering, GITAM Institute of Technology, GITAM (Deemed to be University), Visakhapatnam, Andhra Pradesh, 530045, India. 3 Department of Mechanical Engineering, Chaitanya Bharathi Institute of Technology(A), Gandipet, Hyderabad, 500075, Telangana, India. 4,5,6 Department of Mechanical Engineering, Prasad V. Potluri Siddhartha Institute of Technology, Vijayawada 520007, Andhra Pradesh, India. 5 th International Conference on Applications of Fluid Dynamics - ICAFD 2020 An Online Conference December 13-15, 2020

2. AA7075 is a candidate alloy which is extensively used in aerospace, defence and automobile applications due to its high strength, but key the problem associated with this alloy is low resistance towards corrosion. In this present investigation Friction stir processing technique has been employed to modify the surface of this alloy because it is a special technique in solid-state welding process which is extensively used for modifying the surface of similar and dissimilar alloys very effectively. In the present work, AA7075-T6 plate is used as a substrate and is friction surfaced by a consumable rod (AA6061-T6) using a manual vertical milling machine. The friction surfaced substrate is subjected to metallographic study to observe the microstructure of the surface. The samples were also tested for hardness, wear and pitting corrosion resistance. The microstructure of the surfaced region revealed the break-up and dispersion of coarse eutectics. It was observed that the corrosion resistance was improved when AA6061 is deposited on AA7075. Keywords: Friction Stir Processing, AA7075, AA6061, wear, corrosion, hardness. Abstract

3. Introduction AA7075 is one of the candidate materials, possesses high strength, fatigue, toughness, and ductility. It is commonly used in aircraft structural parts. The primary alloying element in this alloy is zinc, and other alloying elements include magnesium and copper. This alloy is not resistant to general as well as stress corrosion. Joining by fusion welding is very difficult. The main reason associated with less corrosion resistance is its precipitates, mainly MgZn 2 which is highly anodic, and another reason is precipitate free zones (PFZ’s), because of this preferential dissolution takes place Many researchers have been trying to improve the corrosion resistance of this alloy by adding Nano powders and modifying the surface of this alloy.

4. Friction stir processing (FSP) is a novel technique which is originated from the FSW technique. It can be extensively used for modifying surfaces Our main intention in this investigation is to improve pitting corrosion resistance by modifying the surface of this alloy. Usually, hard tools are commonly employed for this purpose, here an attempt has been made by using a softer tool. In this study, AA60601 is used as a tool for the surface modification of AA7075. As we know AA6061 is precipitation hardened which contains magnesium and silicon.

5. Chemical composition of the commercial AA7075 and AA6061 used in this investigation. Experimental Procedure Material Cu Mg Si Fe Mn Cr Zn Ti Al AA7075 2 2.9 0.4 0.5 0.3 0.25 5.7 0.2 Balance AA6061 0.31 0.69 0.53 0.23 0.33 -- -- -- Balance

6. Friction stir Processed AA7075-T6 plate using AA6061-T6 Tool.

7. Results and Discussions Microstructure studies Optical micrograph of AA6061-T6 showing Mg 2 Si (black) and Fe 3 SiAl 12 (gray) particles.

8. Optical micrograph of AA7075. MgZn 2

9. Coating thickness of friction stir processed AA7075-T6 by AA6061-T6.

10. Optical micrograph of FSPed AA7075-T6 with AA6061-T6 showing Mg 2 Si particles(dark).

11. Hardness studies Mirco Vickers hardness of AA7075-T6, AA6061-T6 and FSPed AA7075-T6.

12. Pitting Corrosion Studies corrosion potentials, Ecorr (mV), SCE of AA7075 alloy in –T6 condition. comparison of corrosion resistance of AA7075 -T6 , AA6061 -T6 and AA7075 -T6 FSPed with AA6061 -T6.

13. Wear studies

14. Conclusions From the present investigation, the following conclusions were made. 1. Optical micrograph of FSPed AA7075-T6 with AA6061-T6, clearly reveals the recrystallized grains that are formed after processing, and it also shows the uniform distribution of secondary phase particles throughout the matrix. 2. Hardness of AA7075-T6 base metal is modified with friction stir processing by using AA6061-T6 as mechtrode. 3. Friction stir processing with AA6061-T6 increased pitting corrosion resistance of AA7075-T6. 4. Wear resistance of AA7075-T6 has been improved as compared with AA6061-T6 and wear resistance of FSPed AA7075-T6 with AA6061-T6 is nearer to the AA7075-T6.

15. Thank You

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