Improving Joint Features and Mechanical Properties of Pinless Fiction Stir Welding of Alcald 2A12-T4 Aluminum Alloy

As a new solid state welding, pinless friction stir welding (PFSW) can be used to join thin-wall structures. In this study, four new pinless tools with different groove distributions were designed and manufactured in order to enrich technological storage of PFSW and obtain sound joint with high quality of alclad 2A12-T4 alloy. The results show that the small-obliquity tool is detrimental to the transfer of plasticized materials, resulting in the formation of kissing bond defect. For the through-groove tool or the large-curvature tool, bigger flashes form on the joint surface and alclad layer is observed in the nugget zone (NZ), deteriorating mechanical properties. Compared with the above-mentioned three tools, using the six-groove tool with rational curvature and obliquity can not only yield sound joint with small flashes and thickness reduction, but also prevent alclad from flowing into NZ, which has potential to weld thin alclad aluminum alloys. Meanwhile, the tensile strength and elongation of joint using the six-groove tool reach the maximum values of 362 MPa and 8.3%, up to 85.1% and 64% of BM.