Mechanical properties and stress corrosion cracking behaviour of AZ31 magnesium alloy laser weldments

An AZ31 HP magnesium alloy was laser beam welded in autogenous mode with AZ61 filler using Nd-YAG laser system. Microstructural examination revealed that the laser beam weld metals obtained with or without filler material had an average grain size of about 12 mu m. The microhardness and the tensile strength of the weldments were similar to those of the parent alloy. However, the stress corrosion cracking (SCC) behaviour of both the weldments assessed by slow strain rate tensile (SSRT) tests in ASTM D1384 solution was found to be slightly inferior to that of the parent alloy. It was observed that the stress corrosion cracks originated in the weld metal and propagated through the weld metal-HAZ regions in the autogenous weldment. On the other hand, in the weldment obtained with AZ61 filler material, the crack initiation and propagation was in the HAZ region. The localized damage of the magnesium hydroxide/oxide film formed on the surface of the specimens due to the exposure to the corrosive environment during the SSRT tests was found to be responsible for the SCC.