Investigation on microstructure, mechanical properties and corrosion behavior of VPPA welded Al-Mg-Mn-Sc-Zr alloy

Variable Polarity Plasma Arc Welding (VPPAW) can be used for the excellent welding of a 6 mm thick Al-Mg-Mn-Sc-Zr alloy, promising for the aerospace applications, due to its favorable welding quality, high production efficiency and small welding deformation. At present, investigations on the corrosion behavior of this type of welded joints are still insufficient. Here, the microstructure, mechanical properties and corrosion behavior of VPPAW-based Al-Mg-Mn-Sc-Zr alloy were systematically studied. The results show that the lowest value of the hardness of the welded joint occurs in the center of the weld, the fracture position of the welded joint is located in the welded region, and the bond zone (BZ) has the poorest corrosion resistance. The ultimate tensile strength (UTS) and welding coefficient of the welded joint are 327 MPa and 74.5 %, respectively. The low strength of the welded joint is mainly due to the combustion of the Mg element, the growth of grain size and the dissolution of second phase particles, resulting in the weakening effects of solid solution strengthening, precipitation strengthening, and grain boundary strengthening. The poor corrosion resistance of the BZ is attributed to the higher density of Fe-rich intermetallic particles and the weaker passivation film in this region.