Multi-objective optimization of input and output process parameters of dissimilar CMT welded joints of AA6082 and AA7075

Abstract

This study utilized dissimilar AA6082 and AA7075 plates to fabricate the cold metal transfer (CMT) welds, and developed a mathematical model to predict the optimized input and output parameters of the weldments. Variance analysis revealed that welding current significantly influenced UTS and microhardness (MH), while the effects of welding speed and gas flow rate (GFR) were minor. Increasing TRS resulted in higher UTS and MH. The optimized values were 87.79 HV for MH, 10.44% for strain, and 168.46 MPa for UTS at a welding speed of 4.01 mm/s, a welding current of 89.95 A, and a GFR of 15.89 L/min. The maximum UTS of 212.55 MPa was achieved at a WS of 8 mm/s, a welding current of 70 A, and a GFR of 18 L/min. The minimum UTS of 146.91 MPa was found at a WS of 4 mm/s, a welding current of 100 A, and a GFR of 18 L/min. The presence and behavior of intermetallic compounds significantly impacted the XRD peaks, providing insights into microstructural changes and phase transformations during welding. Localized heating and cooling during the CMT welding process led to grain refinement, influencing precipitate behavior. The effect of welding current on grain size within the WFZ was consistent and largely independent of the Al-alloy plates’ locations, indicating that the temperature experienced by the WFZ remained relatively unaffected by the base plate’s specific region. This consistency in grain size reduction across different locations highlights the robustness of the welding process in maintaining temperature control within the WFZ.