Resistance spot welding of die-cast and wrought aluminum alloys: Improving weld spot quality through parameter optimization

Abstract

Welding aluminum castings is known for a high sensitivity for hydrogen-induced weld porosity. Research has shown that the porosity detected in mixed material resistance spot welds between die-cast and wrought aluminum is predominantly classified as solidification porosity. But, nugget penetration depths into the wrought aluminum alloy are low. In this work, the effect of a forging electrode force during welding current time t_i or after the welding current is shut off on weld spot characteristics is investigated, when resistance spot welding (RSW) mixed material joints between EN AC-43500-T6/T7 and EN AW-6082-T6. A current cut-off test based on a welding profile according to VDA 238–401 reveals a welding current time t_i between 60 ms ≤ t_i ≤ 80 ms as relevant for porosity detection in cross-section analysis. Based on this, different welding profiles are tested, and resulting weld spot characteristics are analyzed when applying chisel tests, cross-section analysis, quasi-static shear tensile tests, and scanning electron microscopy. The application of a forging electrode force reduces weld spot porosity in RSW significantly, while a current downslope leads to an increase. Further, the application of a forging electrode force during welding current time leads to a significant decrease in the standard deviation of s = 1.07 kN to s = 0.08 kN in shear tension force, although the mean shear tension force is increased marginally from 7.07 kN to 7.15 kN. Yet, an increase in weld penetration depth ≥ 20% into EN AW-6082-T6 is only achieved when reducing the initial electrode force to 5 kN and initiating forging electrode force during t_i.