Mating electrodes made of copper alloys are commonly used for welding galvanized steel sheets used in the production of car bodies. These alloys are characterized by high mechanical properties, a high level of electrical and thermal conductivity as well as the stability of these properties under changing conditions of current, thermal and mechanical load. Much careful attention was paid to the essence of the ongoing structural changes as well as to the mechanical properties in the welding process (RSW – Resistant Spot Welding) of steel sheets, including high-strength ones. There is a lack of research on structural changes and the related mechanical properties occurring in welding electrodes made of copper alloys caused by the welding process.
This study is devoted to these issues and contains a critical review of the research results enabling a better understanding of the relationships between the structure and properties of welding electrodes caused by the cyclic welding process. In order to illustrate the phenomena occurring during the welding process, both in the material to be welded and in the tip electrodes, hardness and structural tests were carried out on electrode samples before and after their exploitation. The data collected in the article supplements a certain lack of information in the literature regarding the microstructural aspects of the welding process of galvanized steel sheets for the production of car bodies. The conducted research may be the starting point for the search for more effective materials for the tip electrodes.

As one of the most promising 3rd generation advanced high strength steels (AHSS), medium Mn steels attract much attention because of their exceptional mechanical property and reasonable cost. However, their application in the modern automotive industry is limited by poor weldability. In this study, 7Mn steel was welded by resistance spot welding (RSW), which was followed by high-temperature annealing to increase the cross-tension property. With this effort, enhanced cross-tension strength (CTS) with a partial interfacial fracture (PIF) mode was realized. During the annealing after RSW that produced martensite, austenitization was realized and then evolved into martensite by the following air cooling. This process produced structure homogeneity across the joint. With respect to the RSW joint, martensite remained the dominant structure after annealing while the diffusion of C and Mn solutes was triggered. With the increase of annealing temperature, the diffusion was enhanced, and the grain boundary embrittlement was reduced, leading to higher CTS.