Effect of addition of stainless steels on the microstructure and properties of SiCp/LY12 resistance spot welding joint

Abstract

SiCp/LY12 composite plates were successfully joined by resistance spot welding (abbreviated as: RSW). 1Cr18Ni9 stainless steel thin slice with 0.12 mm thickness was placed between the spot electrode and weld specimen in the process of welding. The effect of stainless steel thin slices on the microstructure and comprehensive properties of joints was investigated comparatively by means of OM, SEM and joint tensile shear test. The results show that, when the specimens are welded directly without adding stainless steel, SiC particles in the joints are not evenly distributed, there have different zones across the weld, including SiC particles sparing zone, SiC particles concentration zone and SiC particles transition zone. By comparison, with the addition of stainless steels, the SiC particles are uniformity throughout the weld. The analysis of tensile shear fracture reveals that when the specimens are welded directly under the best welding parameters, the diameter of weld nugget is 4.3 mm, the button shape after tearing is irregular elliptical-type, and the tensile shear force of joint is 1242 N. While, when welded by adding stainless steels, the diameter of weld nugget is 5.3 mm, the buttons shape is regular circle with a tensile shear force of 1693 N. It can be attributed to produce more heat and well mobility in the course of spot welding. Moreover, joining of stainless steels can cause equalization of spot electrode pressure. The research has led to the discovery of apparent improvement of microstructure and properties in RSW joint of 15%SiCp/LY12 composites due to the addition of stainless steels.