Microstructures and Mechanical Properties of Butt Joint of A356/6005A Dissimilar Aluminum Alloy by Pulse MIG Welding

The microstructures and mechanical properties of the butt joint between cast A356 aluminum alloy and wrought 6005A aluminum alloy welded using ER5356 welding wire by the method of DC pulse metal-inert arc gas (MIG) welding were investigated by optical microscopy (OM), scanning electron microscopy (SEM), equipped with energy dispersive spectrometry (EDS) and tensile property tests. The fracture occurred at the heat effected zone and weld zone mainly for the A356/6005A welded joint. Its ultimate tensile strength, elongation and welded joint strength coefficient were 219 MPa, 6.21% and 0.7, respectively. And the welding strength coefficient was about 0.7. The fusion zone was characterized by dendritic structure and composed of α-Al, Mg₂Si and Mg₅Al₈ phases. The fusion zones in the A356 and 6005A alloys showed different microstructure characteristic. For the fusion zone in the A356 side, its width was over 500 μm and consisted of island-shaped (α-Al + Al–Si) eutectic and coarse Si particles. The fusion zone in the 6005A side which exhibited transition microstructures and consisted of (α-Al + Al–Mg–Fe–Si + Al–Fe–Si) mixed phases was about 80 μm in width.