Resistance spot welding of die-cast and wrought aluminum alloys: the influence of experimental setup-dependent heat field manipulation on weld spot quality when joining EN AC-42.400 to EN AW-6082

Abstract Resistance spot welding (RSW) is an economic, robust, and reliable welding process for joining thin steel sheets and structural components. Despite RSW of aluminum is already applied in automotive industry, resistance spot welds between dissimilar aluminum alloys are a major challenge, because small changes in alloy composition can already lead to significant differences in chemical and physical properties. In previous research, resistance spot welds between aluminum alloys of the 6000 series and die-cast aluminum are described as atypical with only poor nugget penetration depth (≤ 20%) into the higher conductive wrought aluminum alloy. This work explores approaches for heat field manipulation in resistance spot welding of mixed material joints between EN AC-42.400 and EN AW-6082-T6 and their effect on weld spot quality. When applying different experiment set-ups, that is electrode material, electrode geometry and workpiece orientation in secondary current circuit, and different welding parameters, differences in weld spot morphology are observed that influence the weld spot properties. Next to the thermal properties of the dissimilar alloys used, the Peltier effect shows a severe influence on weld nugget location and quality. Hence, the mechanical properties are deteriorated and fall below recommended threshold values. Although the use of dissimilar electrode materials enables an increased reproducibility of weld spot properties the effect on weld spot quality and penetration depth into EN AW-6082 is only marginal. The application of electrodes with dissimilar radii increases nugget volume and diameter, but also, an increased weld expulsion probability is found at high energy inputs. Further, shunting is favored, which alters the quality of previous weld spots. Here, doubling the spot distance not only leads to an increase in penetration depth into EN AW-6082 (37% of sheet thickness), also a significant increase in weld spot quality is observed.