Optimization of joint strength for dissimilar low-carbon equivalent steel to multiphase steel resistance spot welds

This study investigated the influence of resistance spot welding (RSW) process parameters on nugget formation and joint strength in dissimilar low-carbon equivalent (LCE) and multiphase (MP) advanced high-strength steel (AHSS) sheets. A factorial experimental design was used to evaluate the effects of welding current, weld time, and cooling time for a multi-pulse weld schedule on cross-tension peak load and nugget diameter. The results indicated that welding current and weld time were the dominant factors that influenced peak load and nugget diameter, and significant interaction effects were observed. The highest peak loads and nugget diameters were obtained within a process window corresponding to welding currents between 7.5 and 10.0 kA and weld times between 130 and 200 ms. Cooling time was observed to influence the transition region between no-weld conditions and expulsion-related conditions, suggesting an effect on failure behaviour. A positive linear correlation between nugget diameter and peak load was identified, indicating that increasing nugget size improved joint strength. However, analysis within the measured nugget diameter range revealed multiple failure modes, suggesting that nugget diameter alone was insufficient for accurately characterizing weld failure behaviour. These findings established a favorable process window for dissimilar AHSS RSW and provide insight into the relationship between process parameters and mechanical performance.