Microstructure and mechanical properties of the joint of 6061 aluminum alloy by plasma-MIG hybrid welding

Plasma-MIG(metal inert gas arc welding) hybrid welding of 6061 aluminum alloy with 6 mm thickness using ER5356 welding wire was carried out. The microstructures and mechanical properties of the welded joint were investigated by optical microscopy, X-ray diffraction(XRD), energy dispersive spectroscopy(EDS), tensile test, hardness test and scanning electron microscope(SEM) were used to judge the type of tensile fracture. The results showed that the tensile strength of welded joint was 142 MPa which was 53.6% of the strength of the base metal. The welding seam zone was characterized by dendritic structure. In the fusion zone, the columnar grains existed at one side of the welding seam. The fibrous organization was found in the base metal, and also in the heat affected zone(HAZ) where the recrystallization occurred. The HAZ was the weakest position of the welded joint due to the coarsening of Mg2Si phase. The type of tensile fracture was ductile fracture.