Observations on the Stress Corrosion Cracking of an Al-5%Zn-2.5%Mg Ternary and Various Quaternary Alloys

Abstract

Abstract Studies were undertaken to test a concept of controlling stress corrosion crack propagation in Al-Zn-Mg alloys through the use of minor alloying additions of elements known to retard hydrogen ion recombination. Previous work suggested that the recombination of hydrogen ions governs the rate of anodic dissolution and, in turn, the rate of crack propagation in these alloys. Results indicated that the concept was invalid since the minor alloying additions themselves exerted a more profound influence on the grain boundary microstructure. Specifically, the microstructural features of grain boundary particle size and interparticle spacing were found to correlate with stress corrosion susceptibility. Auger electron spectroscope studies also revealed a correlation between the concentration of Zn and Mg within the precipitate-free zone and the susceptibility to cracking.