Mechanical and Microstructural Investigation on Friction Stir Welded Aluminium – Steel Dissimilar Joints

Introduction: This study investigates the application of friction stir welding (FSW) to join aluminium alloy 6061 with high-strength interstitial free galvannealed steel. The effects of tool rotational speed, traverse speed, and shoulder diameter on the mechanical properties of the joints were examined. Methods: Optimal conditions were identified, with a tool rotational speed of 1200 rpm and a traverse speed of 100 mm/min, significantly enhancing the ultimate tensile strength (UTS) and impact strength of the joints. The optimized parameters resulted in UTS values reaching up to 320 MPa. Microstructural analysis revealed substantial grain refinement in the stir zone (SZ), leading to increased micro-hardness values of up to 150 HV, compared to the base materials (BM) and heataffected zones (HAZ). Results: Micro-hardness often rises as a result of grain refining brought on by tool rotation in the SZ and TMAZ. However, as the indentation distance from the SZ grows, the micro-hardness declines, especially in the HAZ and the BM's grain-coarsened region. The distribution of micro-hardness also shows that dynamic recrystallization in the FSW leads to considerable grain refinement in the SZ. SZ is, hence, harder on the microscale than BM and HAZ. Conclusion: The findings highlight the critical role of process parameter optimization in improving the mechanical performance of aluminium-steel dissimilar joints.