Effect of tool rotational speed on friction stir spot welds of AZ31B Mg alloy to AISI 304 stainless steel

Abstract

Abstract AZ31B Mg alloy were welded to AISI 304 stainless steel (which is a very challenging task because of their huge different chemical and physical features) by friction stir spot welding (FSSW) at different tool rotation speeds (700, 1000, and 1300 rpm) while keeping other conditions the same. Welds were evaluated and compared by examining their cross-sectional geometry, XRD pattern, tensile shear strength, fracture way and area. From cross-sections of welds, it was obtained that joining area expanded when speed was enhanced and the weld made through 1300 rpm had the largest one. Therefore, weld fabricated with the highest speed of 1300 rpm displayed the biggest tensile shear load of 3741 N while that manufactured with the lowest speed of 700 rpm possessed the lowest of 2430 N. All welds showed tensile shear type fracture and fracture occurred from the hooking regions where joining took place. From the fracture joint region, the weld of 700 rpm had the smallest joined area, whereas that of 1300 rpm showed the biggest. Higher speed produced a stronger joint, which agreed with a bigger bonding area and broken joint region. Also, joint became more ductile with increasing speed. Some phases were detected in joints.