Stress corrosion cracking of gas-Tungsten arc welds in AZ31 magnesium alloy

AZ31 Mg-Alloy sheet was welded using a Gas-Tungsten Arc (GTAprocess over inserts containing 2.3-9.3 wt% Al. The welded specimens were susceptible to SCC in distilled water, with susceptibility increasing with decreasing weld metal Al (or particle concentration. Primary stress corrosion cracks initiated at the weld metal-HAZ interface by stress-Assisted localised dissolution and propagated through the weld and base metals by Transgranular and Intergranular H-Assisted Fracture (TG-HAF and IG-HAFrespectively. The IG fracture mode may be intrinsic to the texture imparted upon the base metal by rolling. The increase in SCC susceptibility with decreasing weld metal Al concentration is contrary to the purported roles of ? particles in promoting localised corrosion and as crack nucleation sites, but corresponds with an increase in the weld-base metal galvanic current density. This implies that the SCC susceptibility of the welded samples is governed by the localised corrosion p rocesses involved in SCC initiation.