Effects of sensitization on environmentally assisted cracking of AA5083-H128 Al–Mg alloy

Abstract

The influence of sensitization on the precipitation behaviour and environmentally assisted cracking (EAC) of AA5083 alloy with the –H128 temper have been investigated. 80 °C/500 h and 80 °C/1000 h sensitized specimens exhibit discontinuous Mg-rich precipitates along the grain boundaries, whereas almost continuous β′ phase is present along the grain boundaries in the 175 °C/100 h sensitized material. EAC susceptibility increases with increasing exposure time and elevated temperature. The relationship between nitric acid mass loss test (NAMLT) values and mechanical test results indicates that specimens with a NAMLT value greater than 25 mg/cm2 exhibit severe EAC. The test environment affects the degree of EAC due to the combined effects of anodic dissolution at the crack tip, hydrogen evolution, and hydrogen embrittlement. AA5083-H128 exhibits lower EAC susceptibility than AA5083-H131, likely due to its lower yield strength. High yield strength can produce more Mg-rich precipitates after sensitization, increase the constraint of the crack tip material and accelerate the diffusion rate of H atoms in the process zone of the crack tip.