Local corrosion behaviour of hybrid laser-MIG welded Al-Zn-Mg alloy joints

Abstract

The local corrosion behaviour of a hybrid laser-metal-inert-gas (MIG) welded Al–Zn–Mg alloy joint is studied using pre-cracked bending samples immersed in 3.5% NaCl solution. To gain insight into the SCC susceptibility in different zones including the base metal (BM), heat affected zone (HAZ) and fusion zone (FZ), the corrosion surface, fractured surface and SCC propagation are investigated experimentally. The results illustrate that the BM in natural ageing (NA) state is more prone to induce SCC than the HAZ, a finding that differs from previous reports that the HAZ is more prone to induce SCC. The reason is explained via the welding process and corrosion method. Influence of post-weld heat treatment (PWHT) on SCC resistance of the hybrid laser-MIG Al–Zn–Mg joint is examined as well. The results show that the resistance of the welded joint to SCC can be enhanced by PWHT. The microstructure change due to PWHT is shown to be responsible for this improvement.