The investigation of mechanical properties of 439 DX51D quality sheets joined by spot resistance welding

In industry, especially in the manufacturing sector, various steel materials are widely used. During production, there is often a need to join these steel parts at certain points. For this joining, some of the most widely preferred joining methods in the mass production sector are spot resistance welding. It is widely used for welding these thin sheet materials together in a durable and reliable way. 439 grade stainless steel plate has high resistance to oxidation, temperature resistance reaching 800-900 degrees. Thanks to its robustness and welding potential at high temperatures, it is ferritic stainless steel that can be used frequently in small household appliances such as water heaters that we use continuously, vehicle exhaust construction and parts where the temperature changes constantly, washing machines, automotive sector and most importantly in the food sector. DX51 galvanised sheet is coated with hot dip galvanising method. This process means applying zinc coating to protect the steel against corrosion. It is usually coated on both sides. DX51 is usually produced from low carbon steel (LC) and used as a commercial grade. The steel grade can also be specified by sub-grades with specific chemical composition and mechanical properties, such as DX51D and DX51D+Z. It can be used in many different industrial and commercial applications such as building construction, automotive, white goods, electrical appliances, packaging, water and gas pipelines, automotive parts, roofing, exterior cladding. In this study, 439 and DX51D steels were joined by electric resistance spot welding method using different parameters. Metallographic investigations and mechanical tests were carried out on the joined specimens. The specimens were prepared by electric resistance spot welding using three different amperes, three different press forces and three different dwell times. In electric resistance spot welding, the current flowing through the electrodes, the force applied by the electrodes to the workpiece and the welding time are the most important basic factors. The combination of these factors with each other and the amount of application determine the quality of the weld. The quality of the weld directly affects the mechanical strength of the parts to be joined. It is aimed to determine the appropriate welding parameters by investigating the strength, hardness and microstructure properties of ferritic and galvanised steels. Tensile test, hardness measurement, microstructure analysis and weld penetration investigations were carried out to determine the mechanical and microstructural properties of the welded specimens.