Structural characteristics of friction stir circumferential spot welding of 3003 aluminum alloy

Abstract

To address the issues of cracks, porosity, and joint softening that are prone to occur during the welding of thin aluminum alloy sheets, this paper proposes a novel friction stir circumferential spot welding (FSCSW) process and designs a ring-shaped tool with a specific tip morphology. Using 2024 aluminum alloy sheets and 1100 aluminum alloy rivets as research objects, the effects of process parameters such as tool rotational speed and dwell time on the weld macro-morphology, material flow behavior, microstructure, and mechanical properties were systematically analyzed. The results indicate that the designed ring-shaped tool effectively enhances heat input and material mixing uniformity by increasing the contact area and strengthening the mechanical stirring action, thereby suppressing typical defects such as porosity and voids. At a rotational speed of 800 rpm, material mixing is the most sufficient, while at 1000 rpm, interface integrity is superior. When the dwell time is 8 s, the thermo-mechanical matching is optimal, the aluminum rivet structure remains intact, and the joint achieves a peak tensile strength of 240 MPa. Excessively short or long dwell times lead to uneven material mixing, interfacial defects, or microstructural softening. In conclusion, reasonable matching of tool rotational speed and dwell time is the key to achieving high-quality aluminum alloy friction stir circumferential spot welded joints.