Plunge Stage Force Reduction in Friction Stir Spot Welding of AA2024-T3 through Implementation of Assistive-Auxiliary Energy

Abstract

The increasing demand for lightweight, high-strength structures necessitates materials with superior strength-to-weight ratios and advanced technologies like Friction StirWelding (FSW). Since its inception in 1991, FSW has been recognised for its ability to produce high-quality, defect-free welds and its status as a green technology. However, the high axial forces required during the plunge stage of FSW present a significant challenge, necessitating large machinery and robust tooling, particularly when welding high-strength aluminium alloys such as AA2024-T3. This study explores the use of auxiliary energy methods to reduce plunge stage forces in AA2024-T3 lap joint samples and assesses their impact on joint mechanical properties and microstructures. Workpiece and tool preheating emerged as effective strategies, achieving maximum axial force reductions of 76% and 62%, respectively. Shear tensile performance was maintained, with tool preheating yielding superior results due to reduced grain coarsening and precipitate dissolution. In contrast, the Electroplastic Effect, despite reducing flow stress by 14%, proved unsuitable due to scalability and energy efficiency challenges. The findings demonstrate that preheating methods significantly reduce force requirements, enhancing the scalability and industrial applicability of FSW. By mitigating the need for large machinery, these methods broaden the material scope and economic feasibility of FSW, offering a viable path for its adoption in engineering applications requiring lightweight, high-strength structures.