Technical Note: Effect of Precorrosion on the Electrochemical Response of Strained Aluminum Alloys Available to Purchase

The aluminum alloy 7075 (typically, in weight percent, 5.5 Zn-2.2 Mg-1.2 Cu-0.18 Cr-balance Al) in the high strength T651 temper (yield strength, 73,000 psi), is generally considered highly susceptible to stress corrosion. It has been observed, however, that corrosion in the absence of applied stress may be initially as damaging as corrosion while stress is applied.^1,2  This has been shown to result from mechanical disruption of the surface, e.g., by machining. Such deformation disturbs the surface grain boundary structure. This disrupted layer must be penetrated by a corrosion process which, because the grain boundaries have been microscopically fragmented, is not accelerated by stress. When this layer has been penetrated by corrosion (precorrosion), intergranular stress corrosion can begin. Precorrosion can then be used as a probe of this disturbed layer. The present experiments are related to the effect of the precorrosion treatments on the observed anodic response of 7075-T651 during...