Effect of discharge voltage on the microstructure and mechanical properties of aluminium alloy AA6061 and mild steel joints by magnetic pulse welding

This study investigates the effect of discharge voltage on the interfacial microstructure and mechanical performance of a thin AA6061 tube and a thick mild steel tube with an extended overlap length of 20 mm to ensure bonding continuity. Successful bonding occurred at 14–15 kV, while 13.5 kV was insufficient for metallurgical joining, and 15.5 kV caused interfacial instability. OM and SEM–EDS revealed a characteristic wavy morphology with iron aluminides and defects within the transition layer. An optimized discharge voltage of 14.5 kV promoted effective jetting and continuous metallurgical bonding, whereas lower or higher voltages resulted in shorter, shallower waves, unbonded regions, and excessive intermetallic growth with pores and microcracks. Silicon in AA6061 reduced the intermetallic thickness by forming a ternary Fe-Al-Si phase at the joint interface, as confirmed by EDS and XRD. On the AA6061 side, EBSD results at 14.5 kV showed fine equiaxed grains from dynamic recrystallization, while the MS displayed elongated grains oriented along the welding direction. The maximum tensile-shear strength of 186 MPa was obtained at 14.5 kV, whereas 14.0 kV and 15.0 kV resulted in lower strengths of 152 MPa and 140 MPa, respectively, indicating a narrow processing window for Al-Fe tubular joints.