چكيده به لاتين
With the aim of reducing the weight of metal structures, especially in automobiles, the use of metals with lighter weight compared to steel and iron alloys has received attention. Magnesium is one of the lightweight metals that has been studied by researchers in recent years. Considering that the predominant joining method for metal sheets in automotive industry is resistance spot welding, this thesis investigates the dissimilar joining of magnesium AZ31 alloy with galvanized steel. Initially, the thickness of the galvanized coating was considered as a parameter, and several experiments were conducted using direct current and alternating current welding machines. Subsequently, the response surface methodology was employed for experimental design, and three parameters (current, time, and force) of the resistance spot welding process were defined at five levels, while other parameters were kept constant. Furthermore, for numerical analysis of the process, a model was simulated using Abaqus software and compared with the dimensions of the welded nugget obtained from the experimental sample in this thesis. To examine the quality and quantity of the samples, mechanical tests and microstructural characterization, including tensile testing, microhardness testing, optical microscopy, and scanning electron microscopy, were employed. The results indicated an increase in tensile strength of the joint with an increase in the thickness of the coating due to the modification of the joint area structure through the diffusion of zinc. In the investigation of the parameters, electrical current was identified as the most influential parameter, and the proposed model, with an error of less than 10%, was capable of predicting the experimental results within the selected range of parameters. In the numerical section, simulation was performed, predicting the height of the welded nugget with an error of 25% and the diameter of the welded nugget with an error of 3%.
