Comparative study on laser welding and TIG welding of semi-solid high pressure die cast A356 aluminium alloy

Aluminium alloys are used extensively in the automotive and aerospace industries. The development semi-solid forming as manufacturing process has offered the opportunity to HPDC cast complex, near net shape, high volume, and high integrity components. The low porosity levels in SSM high pressure die castings (HPDC) improves the weldability of these components. The aim of the current research was to perform a comparative study of laser and TIG welding of SSM HPDC aluminium alloy A356. SSM slurries were prepared using the CSIR Rheocasting System and plates of 4mm × 80mm × 100mm were HPDC. Plates in as cast (F), T4 and T6 heat treated conditions were butt welded using a Nd:YAG laser and constant current AC TIG welding. The microstructure and micro-vickers hardness (MVH) properties of the welds were investigated. It was found that the laser welding processes yielded a finer dendritic fusion zone and a much smaller heat affected zone (HAZ) compared to the TIG welds. The HAZ for both the laser and TIG welding was composed of mainly remelted eutectic and substructural changes that were picked up from the MVH profiles. The TIG welding process used was not well suited for eutectic alloys because of the lower energy density. This resulted in partial melting of the root, due to the longer period required for melting the eutectic structure. Collapse of the root and incomplete fusion was observed. The laser welding process was found to be more effective in welding A356 aluminium alloys because of the higher energy density of the process.