Material characterizations of mild steels, stainless steels, and both steel mixed joints under resistance spot welding (2-mm sheets)

Resistance spot welding is an essential welding mechanism for joining two or more metal sheets together in automotive industries. The mechanical assemblies are easily joined at discrete spots using high current flow through the area of concentration. It is easily achieved by compressing the base metals together to a certain pressure using copper electrode caps and allow the high current to flow through the concerned areas. The heat generation due to the current flow causes the metal sheets to be fused and consequently form bonds between base metals. The molten areas of base metals undergo solidification process by itself when the current flow is utterly stopped. Basically, the weld growth in any joint is determined by its process-controlling parameters, particularly the welding current, weld time, electrode force, and electrode tip. In these experiments, the welding current and weld time variations were carried out to characterize the weld growth for three types of joints mainly for stainless steel, mild steel, and both steel mixed joint. A pneumatically driven 75-kVA spot welder was used to accomplish the entire welding processes, and the welded samples were later subjected to tensile, hardness, and metallurgical tests to relate the diameter growth, loading force during tensile test, failure crack initiation, post-failure crack propagation direction, macro and microstructural changes, and also the hardness changes due to solidification process. Assessing the experimental results of 2-mm thickness of materials revealed that the welded areas’ characteristics have been varied from its original states to enriched states, in terms of shearing strength and hardness distribution as well as the microstructural orientation.