Investigating the effect of the chemical composition of resistance spot welding electrodes on the life of the electrode and the mechanical properties of the welded spots of galvanized steel sheet

In this research, the effect of Cu-Al2O3 and Cu-Cr-Zr resistance spot welding electrodes on the microstructure and mechanical properties of the resistance spot welded (RSW) galvanized steel sheets as well as the service life of the electrodes have been investigated. For this purpose, specimens of DX54-D low-carbon steel sheets with a thickness of 0.7 mm were joined using RSW process. In order to check the mechanical and metallurgical properties of the electrodes and evaluate the quality of the welds, tensile-shear and microhardness tests were used. The weld nugget diameter, maximum force, fracture energy, and failure modes were also investigated. Microstructural investigations were carried out by optical and scanning electron microscopy on welded specimens and electrodes. According to the microstructural investigations, the base metal had a completely ferritic structure, and in the weld metal and the heat-affected area, some Widmannstatten ferrite was observed. Microstructural studies revealed that Cu-Zn compounds were formed on the tips of the electrodes. The type of failure in all welds was circumferential.