Stress corrosion cracking (SCC) susceptibility of Al-Zn-Mg-Cu-Zr base 7010 alloy of two different tempers viz. T6 (peak aged - two step aging) and T73 (over aged - three step aging) have been investigated in air and an aqueous environment (non-deaerated 3.5 wt.% NaCl solution) by slow strain rate testing (SSRT) as well as U-bend testing. The tests have been carried out at 10-5/s and 10-6/s strain rates. In over aged temper (T73), the alloy exhibits substantial improvement in SCC resistance with minimal reduction in the ultimate tensile strength as compared to the peak aged temper (T6). For example, percent reduction in area of peak aged samples dropped from 9.9 % (in air) to 3.3 % (in environment), whereas percent reduction in area of over aged samples dropped from 28.1 % (in air) to just 24.4 % (in environment) when tested at a strain rate of 10-6/s. U-bend test results are also in conformity with the SSRT results. Fractographs of samples tested in air and the environment revealed mixed mode of failure for both the treatments. However, the over aged samples as compared to the peak aged samples showed greater ductile mode of fracture. This appears to be a clear benefit of the over aging process.

Subject
Test methods, Strain rate, Materials, Sodium chloride solution, U bends, Mechanical failure, Risk reduction, Aluminum alloys, Grain boundary, Alloys, Stress corrosion cracking, Aging, Ductility
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2002
Association for Materials Protection and Performance (AMPP)
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