Investigation of resistance spot welding performance of galvanized steel sheet and magnesium alloy (AZ31B) sheet used in the automotive industry

In this research investigates the weldability of 2 mm thick AZ31B magnesium alloy and 1.5 mm thick Erdemir 1314 grade galvanized steel sheets, which have different metallurgical properties, using spot resistance welding commonly employed in the automotive industry. Magnesium alloys, which are lighter than aluminum alloys and share some characteristics with them, are being explored as alternatives to aluminum in the automotive industry. Therefore, spot welding was conducted with galvanized steel, a widely used material in automotive manufacturing, aiming to expand the application of magnesium alloys in automotive applications as an alternative to aluminum. Welding was applied using spot resistance welding under conditions prepared according to TS EN ISO 14273 standard, and it was observed that consistent results were not obtained due to rapid oxidation of magnesium. In the literature review, it was found that there is insufficient research on a method previously unexplored, which involves applying spot resistance welding in an oxygen-free environment. To achieve this, a cabin was constructed around the spot welding machine and filled with argon gas to minimize the oxygen content. Welding was repeated in this controlled environment to prevent oxidation. Welding parameters such as welding time, welding current, and compression time were kept constant, and the microstructures of the welded joints were analyzed to determine the optimum values. In the experiments, samples that underwent welding were subjected to tensile testing to determine their mechanical properties. After cutting and polishing the samples using a cutting machine, their microstructures were examined in detail through XRD and SEM analyses, and Vickers hardness values were measured. The images revealed that the core structure was asymmetric and the bonding around the core was irregular. Pores were observed in the core region due to the penetration of Zn element melting into the magnesium interface. The reason for this situation has been identified as the different melting points of the samples.