Influence of Spot Welding Parameters on Al-Si Coated 22MnB5 for Automotive Application

The application of press hardening steels (PHS) Al-Si coating has been increasing in body in white vehicles as an approach to meet the demands of safety and CO₂ reduction regulations. The vehicle structures with PHS largely depend on the integrity and the mechanical performance of the spots weld. During the spot welding process, intermetallic phase may appear in function of the chemical composition of the steel and coating. One of these intermetallics is the Fe-Al phase which brittleness decreases the strength of the weld joint. In this study, resistance spot welding (RSW) experiments were performed in order to evaluate the influence of the welding parameters of single-lap joints PHS - 22MnB5 steel grade. Welded samples of the Al-Si coated PHS steel as received, i.e., before any heat treatment and stamping, were evaluated by means of glow discharge optical emission spectroscopy (GDOES) technique that allows a quick and accurate evaluation of the chemical composition profile along the spot weld thickness. The GDOES results showed that the squeeze welding parameter has the higher influence on cupper diffusion at the Al-Si-Fe layer. The pre-burn current and welding current showed the higher influences in Fe-Al diffusion. The pulse technique and post-heat treatment had had the lower influences in Fe-Al diffusion.