Welding Journal Research Supplement

Abstract

High-pressure die-cast (HPDC) aluminum alloys are widely regarded as a promising material for next-generation lightweight automotive structures. Compared to large, integrated die-cast bodies, adopting a modular design in which multiple small castings are joined by resistance spot welding can significantly reduce both manufacturing complexity and maintenance costs. However, the base material (BM) of HPDC aluminum alloys exhibits microstructural inhomogeneity because of the random distribution of eutectic Si networks and α-Al dendrites. This inhomogeneity leads to the formation of partially melted zones (PMZ) and fully melted zones (FMZ) with varying thicknesses under different welding thermal cycles, resulting in inhomogeneous nuggets. To clarify the nugget formation mechanism and microstructural characteristics under the coupled influence of BM inhomogeneity and welding thermal cycles, this study compares two typical processes: multi-pulse (MP) and single-pulse (SP), and systematically analyzes the nugget morphology, microstructure, and growth mechanism under each condition. The results show that the PMZ exhibits only slight differences from the BM. In contrast, the FMZ differs from the BM in that it develops new columnar grain zones and equiaxed grain zones. At the same nugget diameter, the continuous heat input from the SP process can reduce PMZ formation and promote greater FMZ development compared with the MP process. However, it also increases the likelihood of crack formation. This study examines the weldability of the HPDC aluminum alloy and provides theoretical guidance for its application in large-scale structural castings for automotive bodies.