Macro-micro numerical simulation and experimental study of Mg-Gd-Y-Zn-Zr alloy fabricated by cold metal transfer wire arc additive manufacturing

Abstract

The Mg-Gd-Y-Zn-Zr alloy components were fabricated by cold metal transfer (CMT) based wire arc additive manufacturing (WAAM). The heat transfer and equiaxed grain growth in the weld pool bonding zone of the alloy were investigated through macro-micro numerical simulation. The results shows, the morphology of the molten pool in the bonding area is ellipsoid with a major semi-axis of 13 mm and a semi-minor axis of 6 mm. The size of the molten pool increases with increasing temperature. With the increase in the number of layers of material added, the high temperature zone is enlarged continuously. This is due to the weakening of the heat dissipation of the substrate and the preheating effect of the first material added on the subsequent material added. The phase field model of equiaxed grain growth during the solidification process of the CMT arc welding pool, was established. The growth of equiaxed crystals in the bonding region temperature gradients of 4.9 °C/m and 3.6 °C/m, the propulsion velocity of 1.5 m/min and 2.3 m/min were simulated, respectively. The further away the molten pool from the keyhole center, the smaller the temperature gradient, the faster the dendrite growth speed, and the more vigorous the dendrite morphology. The unique layered processing method and Marangoni effect of the melting pool in the bonding zone of CMT-WAAM arc additive promote the β-Mg24(Gd,Y)5 and RE-rich phases of body-centered cubic structure. These precipitated phases are evenly distributed at the grain boundaries, it hinders the migration of grain boundarie st, which in turn inhibits grain growth.