Effect of heat treatment on improving the stress-corrosion cracking resistance of 7475 alloy

The effect of heat treatment on improving the resistance to stress-corrosion cracking (SCC) of 7475 alloy was investigated in relation to localized corrosion behavior, strained electrode property and precipitation microstructure. The resistance to SCC of 7475 alloy can be enhanced by shorter-time treatments of over-aging and reversion from the T6 condition, with little loss of strength. The constant extension rate technique (CERT) used for a SCC test of this alloy is available for a rapid method to determine ranking of the heat-treated materials respect to SCC resistance. Preferential grain boundary attack occurs in the T6 material, and its groove acts as sharp notch for initiation of intergranular SCC in the specimen stressed in ST direction. However occurrence of transgranular SCC is observed during CERT test of T6 specimen in L direction. Changes in the resistance to SCC by the heat treatments have been explained in terms of homogeneity of slip deformation and concentration of anodic dissolution at the grain boundaries.