Computer-aided cooling curve thermal analysis and microstructural characterization of Mg-Gd-Y-Zr system alloys

The solidification pathways of Mg-Gd-Y-Zr (GW) alloys with various Y and Gd concentrations were investigated by using a computer-aided cooling curve thermal analysis system, and the solidification microstructure and phase constitution of the investigated alloys were characterized by means of SEM, EDX, and XRD. The results show that the solidification microstructures of GW alloys are mainly composed of alpha-Mg matrix and eutectic Mg-24(Gd,Y)(5) phase, which forms through a univariant reaction: liq. -> alpha-Mg + Mg-24(Gd,Y)(5) during alloy solidification. Based upon thermal analysis results, the hot tearing susceptibility (HTS) and semi-solid formability of Mg-Gd-Y-Zr alloys were evaluated as well. It is predicted that the HTS of GW alloys first increases and then decreases with increasing Gd, Y content. Moreover, the increasing Gd, Y content also decreases the temperature sensitivity of solid fraction, -df(s)/dT, of GW alloys, and thus, improves the semi-solid formability of these alloys. (C) 2014 Elsevier B.V. All rights reserved.