The influence of welding parameters and corrosive environment on the joint strength of resistance spot-welded mild steel sheets

Abstract

In the present work, mild steel sheets consisting two batches were welded by resistance spot welding at different welding parameters and exposed under different environments. The 5% sodium chloride brine was used in the salt spray test, produced a whole rusty surface on the tested specimens (batch 2). The welding joints were subjected to tensileshearing test in order to determine the strength of the welded joints from ambient and in corrosive environment. In addition, hardness measurement and microstructural fracture examinations were carried out in order to examine the influence of both environments to the shearing strength. Tensile-shear test showed significant differences on the failure load between these two batches where corrosion had affected the surface strength of the welded steel. Hardness measurement results indicated that welding nugget gave the highest hardness followed with the heat affected zone then the parent metal. Differences between the non-corroded and corroded hardness values are quite obvious but with slight margin. Microstructural analysis revealed that the deformations took place during tensile-shear test. Fracture path was made starting from the fracture tip where microvoid coalescence. As the strain in the material increases, the microvoids grow, coalesce, and form a continuous fracture surface.