Comparative Analysis of MIG and TIG Welding on AA7075-T6 Aluminum Alloy: Microstructure, Mechanical Properties, and Corrosion Behavior

In this work, AA7075-T6 aluminum alloy 6 mm thick were welded using both metal inert gas (MIG) and tungsten inert gas (TIG) processes with ER5356 filler metal. The welded joints were characterized through optical and scanning electron microscopy (SEM), Vickers microhardness testing, tensile testing, and immersion corrosion testing in aggressive chloride solution. MIG welded joints exhibited superior microstructural integrity with defect-free solidification and formation of a distinct "bleed band structure" at the weld metal (WM)/heat-affected zone (HAZ) interface, indicating optimal metallurgical bonding. In contrast, TIG welded joints showed solidification discontinuities including elongated shrinkage cavities and subgrain structures in the partially melted zone (PMZ). Hardness measurements revealed significant reduction in both processes, with MIG joints showing 25-40% decrease compared to 13-31% for TIG joints in the HAZ. Tensile testing demonstrated that MIG joints retained 58% of base material (BM) ultimate tensile strength (UTS) versus 51% for TIG joints, while TIG joints exhibited higher elongation and strain hardening capacity. Corrosion testing revealed formation of conical-shaped corrosion products on weld zones (WZ), with MIG joints showing increased precipitation sites. MIG welding proves superior for joining 6 mm thick AA7075-T6 plates, offering better microstructural integrity and mechanical performance due to higher heat input and effective cathodic cleaning action. The absence of solidification defects and formation of homogeneous bleed band structure make MIG the preferred process compared to the TIG process for welding of AA7075-T6