Effect of temperature of humid air on susceptibility of hydrogen embrittlement and initiation criterion of intergranular cracking in 7075-T6 aluminum alloy

Abstract

The effect of test temperature on the susceptibility to hydrogen embrittlement (HE) of a high-strength aluminum alloy 7075 with T6 (peak-aged) temper was examined using the slow strain rate technique (SSRT) under a strain rate 1.39×10−6 [1/s]in 65% relative humidity air at temperatures between 10°C and 80°C. On the basis of understanding the condition among stress, strain and time leading to intergranular cracking (IGC) and its temperature dependence, the controlling criterion of IGC initiation by HE was studied. The HE susceptibility increased with increasing temperature and the IGC extension (initiation and propagation) was more promoted. Both the unstressed pre-exposure time in 90% relative humidity air at 30°C and the elastic deformation time in SSRT tests had little effect on the embrittlement behavior. The time parameter defining the IGC initiation was recognized as the plastic deformation time ti (p) until reaching the maximum load. The activation energy evaluated from Arrhenius plots of 1/ti (p) was 16.4 [kJ/mol], nearly equal to the reported value for lattice diffusion of hydrogen in a pure aluminum or alloy 7050-T6. It is supported from these results and analysis that a high hydrogen concentration attained at the site near surface by lattice diffusion controls the IGC initiation.