Metal transfer modes for Wire Arc Additive Manufacturing Al-Mg alloys: influence of heat input in microstructure and porosity

Wire Arc Additive Manufacturing (WAAM), an additive manufacturing technology for the manufacture of medium-to-large size metallic parts, is generating great interest. This technology employs aluminum alloys that are of immense interest for manufacturing, due to their high strength-weight ratio, corrosion resistance and utilization in different industries. Among these materials, some of the most widely used in various industrial fields are alloys classified within the 5000 series that are of good weldability and, consequently, very suitable for WAAM technology. In this paper, aluminum alloy 5356 is analyzed in the Gas Metal Arc Welding (GMAW)-based WAAM technological process. From among the various recommended working modes of different manufacturers, three working modes for aluminum alloys are compared: pulsed-GMAW mode, Cold Arc mode and pulsed-AC mode. To do so, test samples composed of single mono-layer weld beads and single-bead walls are manufactured using each working mode and micro and macro-structural properties, geometrical shape and porosity levels of the finished products are evaluated. As a novelty, this paper includes pulsed-AC as a new transfer mode for application on aluminum. Not only does it show its viability for the manufacture of parts by WAAM, but it also allows the reduction of the presence of pores by more than six times compared to Cold Arc mode and ten times compared to pulsed-GMAW mode. This aspect makes it a very attractive mode for use on this aluminum alloy.