The Separation of Corrosion and Stress Effects in Stress Corrosion: The Critical Role of Surface Preparation Available to Purchase

The stress corrosion behavior of an Al-Zn-Mg-Cu alloy (7075) has been investigated. Under certain conditions of surface preparation, corrosion alone is found to cause a major diminution in subsequent stress corrosion life. For example, in 7075 in the T651 temper with an as-machined surface finish, the deleterious effect of corrosion is independent of the application of load during the first 80% of its normal stress corrosion life. Only during the last 20% of the normal stress corrosion period is it necessary to apply a load. It is during this latter period that true stress corrosion, as normally defined, can be said to occur. These observations do not result from residual tensile stresses in the material; rather, they are shown to be due to disruption of the grain boundary structure at the surface by machining. The beneficial effects of shot peening and other mechanical surface treatments probably also derive from similar distortions.