Probability distribution of life times of stress corrosion cracking of 7075 aluminum alloy.

Life time to stress corrosion cracking (SCC) of an aluminum alloy A7075-T6 in 3.5%NaCl solution or in pure water was measured under a stress along short transverse direction. SCC process is divided into crack initiation stage and crack propagation stage, and each stage is analyzed by the Weibull's distribution method. In NaCl solution the life time for each stage can be described by a composite Weibull's distribution. The shape parameter of mode 1 in the region with shorter life time is larger than unity, and that of mode 2 in the region with longer life time is close to unity. On the other hand, the life time in pure water follows a single Weibull's distribution with the shape parameter around unity. An average life time is smaller in NaCl solution than in pure water by a factor of 2 to 4. In SCC process of mode 1 in NaCl solution, cracks nucleate at the intergranular corrosion pits.