Study on RSW of Zn-Al–Mg-Coated DX54D Steel

The increasing utilization of Zn-Al–Mg-coated steel in automobiles has been increasing due to its exceptional formability and corrosion resistance. Resistance spot welding (RSW) is the predominant joining technique employed in automotive body manufacturing; thus, it is essential to investigate the RSW characteristics of Zn-Al–Mg-coated steel. The present study involves the implementation of a simulated welding window and welding window experiment for RSW on the ZF, ZM45, and ZM35 plates. Subsequently, experiments were conducted to evaluate electrode life and welding stability. Ultimately, the obtained results were thoroughly analyzed and discussed. The results indicate that the welding window is slightly smaller than the simulated welding window. The weldable current range for the ZM35 and ZF plates is 2.4 KA, while for the ZM45 plate, it is 2.1 KA. Both shear-tensile and cross-tensile specimens at points B and E exhibit pull-out fractures, with point B fracture occurring in the HAZ and point E fracture happening at the junction between BM and HAZ. The microstructure of the BM consists of ferrite and pearlite, while HAZ-A exhibits a microstructure comprising ferrite and martensite. HAZ-B displays a fine martensitic structure, whereas HAZ-C exhibits a coarse martensitic structure. The FZ is characterized by an entirely lath martensitic microstructure. It is noteworthy that neither coating thickness nor type significantly influences the resultant welding microstructure observed during this study. Microhardness measurements indicate that points B and E in BM exhibit values around 100 HV, whereas FZ demonstrates approximately 210 HV hardness levels. The electrode life for the ZM45 and ZF plates is 1000 points, whereas for the ZM35 plate, it is extended to 2000 points. At point G, both the ZM45 and ZM35 plates exhibit stable welding performance.