STRESS-CORROSION CRACKING IN EQUIAXED 7075 ALUMINUM UNDER TENSION ANDTORSION LOADING

The environmental response of commercially produced high-strength Al a lloys, such as 7075, depends strongly on the anisotropy of the grain s tructure. Minimum resistance to both stress-corrosion cracking (SCC) a nd hydrogen embrittlement is observed in the short transverse directio n of the ''pancake'' grain structure in commercially produced alloys. It has not been established, however, exactly how the morphology of th e grain structure mediates the SCC response or the SCC mechanism. Ther efore, stress-corrosion testing of a high-purity 7075 Al alloy (low in Fe, Si, and Cr), having equiaxed grains, under tension (mode I) and t orsion (mode III) loading in a solution of 1N AlCl3 has been performed . The SCC results in the two loading modes, including fractography, ap peared to suggest that the predominant processes of SCC were hydrogen embrittlement in mode I and anodic dissolution in mode III, in agreeme nt with prior work on a commercially produced 7075 alloy, but that sev ere corrosion during longer tests renders those results unsuitable for threshold determination in this very aggressive testing environment.