Effect of Welding Speed on Microstructure and Properties of 7075-T6 Aluminum Alloy Pulsed MIG Welded Joints

The objective of this study was to systematically investigate the effect of welding speed on the microstructure, mechanical properties, and corrosion behavior of 7075-T6 aluminum alloy similar joints. Pulsed metal inert gas (P-MIG) welding with ER5356 filler wire was employed as the methodology to fabricate the joints, with welding speed as the sole variable parameter (450, 500, 550, and 600 mm/min) while maintaining constant welding current and voltage. The key results showed that increasing welding speed refined the dendritic structure in the weld zone (WZ) and promoted a more uniform distribution of precipitates. The tensile strength first increased and then decreased, reaching a maximum of 257.7 MPa at 550 mm/min, with a corresponding elongation of 8.1%. The microhardness of the WZ increased from 91 HV0.1 (450 mm/min) to 107.4 HV0.1 (600 mm/min). Corrosion resistance, assessed via intergranular corrosion tests and electrochemical analysis, varied significantly with welding speed; optimal performance was obtained at 450 mm/min, while the poorest occurred at 550 mm/min due to variations in precipitate distribution and passive film stability. The conclusion is that an optimal welding speed of 550 mm/min achieves the best balance between mechanical strength and ductility by refining the microstructure, while the corrosion resistance is primarily governed by the electrochemical activity of grain boundary precipitates induced by the welding thermal cycle.