Effects of Tool Plunging Path on the Welded Joint Properties of Pinless Friction Stir Spot Welding

Four tool plunging paths including a one-time path and three step-by-step were designed to study the effects of on welded joint properties pinless friction stir spot welding (PFSSW). The appearance, cross-sectional microstructure, temperature, microhardness, tensile shear failure load PFSSW thin copper sheets under different explored. Furthermore, fracture modes joints analyzed. Studies showed that 1 (plunge total depth at one time) produced largest range stirring zone, but grains in zone larger width thermal-mechanical affected was smaller. Path obtained highest peak temperature during process, 3 1/3 + plunge 2/3 depth) gained lowest temperature. greater initial amount tool, faster rise rate stage. loads for 1, 2 1/2 depth), 3, 4 8.65 kN, 8.15 8.25 8.85 respectively. 2.3% higher than 1. all nugget pullout fractures. morphology indicated type ductile fracture. proposed this work extends traditional process. findings can provide reference selection design PFSSW.