Stress-corrosion cracking susceptibility of AZ31 alloy after varied heat-treatment in 3.5 wt.% NaCl solution

The stress corrosion cracking behavior of a commercial AZ31 magnesium alloy after T5 and T6 heat treatments under a vacuum of 10(-3) torr has been evaluated via slow strain rate tensile tests in an aqueous 3.5 wt.% NaCl solution. The experimental results show that this material displays a high sensitivity to stress corrosion cracking. The fractured surface was consistent with a significant transgranular component. Double-line cracking that resulted from twinning could be readily spotted on the cleavage plane. The presence of such deformation twins accompanied by the formation of voids is the main reason for the stress corrosion cracking susceptibility of this alloy. The disappearance of twins after artificial aging at 260 C for 4 h significantly improves the corrosion resistance, increases the breakdown potential difference Delta phi (thus lowering the pitting tendency), and decreases the corrosion current density in a 3.5 wt.% NaCl solution.