Slow strain rate stress corrosion cracking behaviour of as-welded and plasma electrolytic oxidation treated AZ31HP magnesium alloy autogenous laser beam weldment

The joining of a thin section AZ31HP magnesium alloy was accomplished by laser beam welding in the autogenous mode using a Nd-YAG laser system. Micro hardness evaluation and slow strain rate tensile (SSRT) tests in air revealed that the weld metal had near-matching mechanical properties corresponding to that of the parent alloy. However, in terms of stress corrosion cracking (SCC) resistance as assessed by SSRT tests in ASTM D1384 solution, the weldment was found to have higher susceptibility compared to the parent alloy. The fracture in the weld metal/fusion boundary/HAZ interface suggested that the failure was due to the grain coarsening at the very narrow heat affected zone. The resistance to SCC of the parent alloy and the weldment specimens was found to improve slightly by the application of plasma electrolytic oxidation (PEO) coating from a silicate based electrolyte.