Effects of backwards thixo-extrusion on the microstructure and mechanical properties of Mg–8.20Gd–4.48Y–3.34Zn–0.36Zr alloy

Abstract

Abstract High temperature mechanical properties of Mg alloys could be improved effectively by adding Zr and rare earth (RE) elements, such as Gd and Y, in Mg matrix. In order to achieve the sufficient utilization of both the volume and properties Mg–Gd–Y–Zn–Zr alloys, semisolid forming (SSF) is one of the most potential methods to realize the near net shape manufacturing. To verify the feasibility of the SSF in manufacturing of Mg–Gd–Y–Zn–Zr alloy products, partial melting and backwards thixo-extrusion experiments of Mg–8.20Gd–4.48Y–3.34Zn–0.36Zr alloy were conducted in semisolid temperature range of it (520~580 °C). The microstructural evolution of this alloy during partial melting and backwards thixo-extrusion was studied experimentally. This alloy exhibited different microstructural morphologies and formability at different extrusion temperature. At lower semisolid temperature (520~560 °C), liquid phase with lower volume fraction cannot improve the ductility of this alloy effectively. At higher semisolid temperature (580~620 °C), handling and transferring of semisolid slurry became quite difficult, owing to the liquid phase with higher volume fraction. The occurrence of liquid segregation and plastic deformation of solid particles during thixo-extrusion at higher semisolid temperature resulted in inhomogeneous distribution of microstructure and mechanical properties of the sample.