The Effect Of Different Heat Treatment On Surface Retrogression On Aluminum Alloy 7075

Hafizuddin, Zuhaimi (2013) The Effect Of Different Heat Treatment On Surface Retrogression On Aluminum Alloy 7075. Project Report. UTeM, Melaka, Malaysia. (Submitted)

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Abstract

Aluminum alloy 7075 have been widely used as structural materials in aeronautical industries due to comprehensive properties such as low density and high strength. However aluminum alloy 7075 are susceptible to local corrosion such as stress corrosion cracking. The corrosion resistance of aluminum alloy 7075 can be improved by developing new heat treatment process in order to obtain optimum mechanical properties and susceptibility to corrosion. In the sample preparation, aluminum alloy 7075 will go to solution heat treatment at 470 °C for one hour and followed by cold water quenching. The quenched samples have preheated for age hardening at 120 °C for 24 hours. Then, the surface retrogression and re-aging process has applied to the sample in the T6 condition to improve the resistance to stress corrosion cracking (SCC) and oil is use as medium for retrogression process. Temperature (170˚C, 190˚C and 210˚C) and time (10 minutes and 30 minutes) is the variable that use for the SRRA process. Samples that have done with surface retrogression method then have re-aging at 120 °C for 24 hours. Hardness value of SRRA is 88.5 HRB that reduced 1% compared to T6(89.4 HRB). Maximum stress of SRRA sample is 634.17 N/mm2 that is sacrificed around 3% when compared to T6 (655.53 N/mm2). Corrosion penetration rate when sample not subjected to force for SRRA sample was improved that is 0.003 mpy compare to T73 (0.011 mpy) and when sample is subjected to 55 kN force the corrosion penetration rate show the increased value which SRRA is 0.0020 mpy and T73 is 0.029 mpy. This properties is influence by precipitation of η-phase and η'-phase inside grain and also inside grain boundary.

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