Effect of heat input on microstructure and mechanical properties of TIG-welded semisolid cast AXE622 Mg alloy

Abstract

The present study investigats the effect of heat input on the microstructure and mechanical properties of the TIG-welded semisolid AXE622 alloy. Three heat inputs, 18 kJ/mm, 21 kJ/mm, and 24 kJ/mm are used, and the corresponding joints referred to as HI18, HI21, and HI24 joints. Results showed that the average grain size in the heat-affected zone (HAZ) (~38 μm, 50 μm, and 67 μm) was more considerable than that in the fusion zone (FZ) (~15 μm, 17 μm, and 18 μm) for the HI18, HI21, HI24 joint, respectively. The volume fraction of the second phases in FZ was significantly higher concerning the HAZ. The eutectic Mg 17 Al 12 phase formed a network structure in FZ of the HI18 joint and fragmented in the HI21 joint, while less fragmentation was observed in the HI24 joint. The volume fraction, the average length, and the width of secondary phases decreased in the HAZ with increasing the heat input. The HI21 joints exhibited the largest tensile strength (~147 MPa) and elongation (~3%) and ruptured in the BM. With increasing the heat input, the hardness decreased in the HAZ and FZ. Besides, the hardness in FZ (~70 HV, 63 HV, and 58 HV) was more significant than that in the HAZ (~ 50 HV, 47 HV, 43 HV) for the HI18, HI21, and HI24 joint, respectively. The beneficial effect of semisolid processing was degraded due to the significant heat input imposed in the HAZ of the HI24 joint. • Semi-solid Mg alloy specimens were successfully produced and TIG-welded in three heat inputs • With increasing the heat input, the grain size increased more significantly in the HAZ. • The least amount of Mg 17 Al 12 phase was formed in the FZ of the HI21 joint. • The HI21 joints exhibit the largest tensile strength, yield stress, and uniform elongation. • With increasing the heat input, the hardness decreased slightly in the HAZ and FZ.