Abstract
The initiation of short-transverse stress corrosion cracking in aluminum alloy 7039-T64 was studied by optical microscopy. Aluminized-plastic replicas were taken from the transverse surface of smooth specimens prior to and periodically during the stress corrosion test. With this technique, it was possible to trace back in time the initiation and propagation of cracks in any given area of the specimen. Dissolution of stressed specimens began at constituent particles resulting in well-defined separations at the particle-matrix interface; in some instances mechanical rupture of the constituents occurred. Stress corrosion cracking started at these interfaces with crack propagation along grain boundaries adjacent to the constituents. It is suggested that the incubation time required to form an incipient stress corrosion crack must be associated with anodic dissolution at specific interfaces, i. e., adjacent to constituents which are cathodic with respect to the matrix.
