Effect of welding speed on the microstructure, mechanical and corrosion properties of 6061/7075 pulsed MIG welded joints

Pulsed metal inert gas welding (P-MIG) was performed on 6061-T6 and 7075-T6 aluminum alloys using ER5356 filler wire. With constant welding current and voltage, the influence of welding speed on the microstructure, mechanical properties, and corrosion behavior of the dissimilar joints was investigated. Tensile strength initially increased and then decreased with rising welding speed. It reached a peak value of 185.99 MPa at 500 mm/min, which is equivalent to 81.7% of the tensile strength of the 6061 base metal. Fracture occurred mainly in the heat-affected zone on the 6061 side and exhibited ductile fracture features. The microstructure and corrosion morphology of the joints were characterized using scanning electron microscopy (SEM), optical microscopy (OM), and electron probe microanalysis (EPMA). The weld zone was primarily composed of equiaxed dendrites, which gradually transitioned into coarse columnar grains toward the heat affected zone. AlFeMnSi intermetallic compounds were also identified. Due to compositional differences, the 7075 side of the dissimilar joint was more susceptible to intergranular, exfoliation, and electrochemical corrosion. The primary corrosion mechanism was attributed to galvanic corrosion between low-potential phases and the matrix. Corrosion behavior intensified with increasing welding speed. Considering both mechanical properties and corrosion resistance, the joint welded at 500 mm/min exhibited the most favorable overall performance. • Heterogeneous P-MIG welded joint was obtained from 6061/7075 aluminum alloys. • Joint corrosion mechanisms were discussed based on immersion corrosion. • Corrosion failure of joint occurs due to galvanic corrosion. • Maximum tensile strength of 185.99 MPa achieved at 500 mm/min welding speed. • 7075-HAZ showed highest corrosion susceptibility with EB rating.