Mechanical performance and haz softening behavior of mig-welded AA6061 aluminium under varying welding parameters

This study examines the effect of welding parameters on the mechanical properties and fracture behavior of MIG-welded AA6061-T6 aluminium joints. Specimens were fabricated using varying welding speeds (40, 50, 60, and 70 mm/min) and currents (110, 115, and 125 A). Tensile tests were performed according to ASTM E8, and fracture surfaces were evaluated macroscopically. The results show that all welded joints experienced a tensile strength reduction of approximately 12–18% compared to the base material, with ultimate tensile strength ranging from 69 to 78 MPa, depending on the applied heat input (1.51–3.60 kJ/mm). In some conditions, elongation increased, indicating enhanced ductility in thermally softened regions. Welding speed was identified as the dominant parameter influencing joint strength, whereas welding current exhibited a comparatively minor effect. Hardness measurements revealed consistent softening in the heat-affected zone (HAZ), which also coincided with the fracture location. SEM fractography confirmed ductile fracture behavior characterized by necking and micro-void coalescence, while higher welding speeds promoted HAZ softening and reduced overall ductility. This study provides a quantitative assessment of conventional MIG welding parameters under industrially relevant conditions, demonstrating that joint integrity in MIG-welded AA6061-T6 is governed primarily by HAZ softening rather than weld metal quality. The findings offer practical guidance for optimizing welding speed and heat input in conventional MIG processes for aluminium alloy structures.