Effects of reheating and subsequent rapid cooling on microstructural evolution and semisolid forming behaviors of extruded Mg-8.20Gd-4.48Y-3.34Zn-0.36Zr alloy

Reheating and rapid cooling experiments, and semisolid compression tests were conducted on extruded Mg-8.20Gd-4.48Y-3.34Zn-0.36Zr alloy using a multistage hot compression test machine. Affected by reheating temperature, heating rate and isothermal holding time, dissolution of eutectic compounds and partial melting occurred during reheating, dynamic arrangement of alloying elements and phase transformation took place during subsequent rapid cooling. These microstructural behaviors not only changed the anisotropy in microstructural morphology of the extruded Mg-8.20Gd-4.48Y-3.34Zn-0.36Zr alloy, but also affected the anisotropy in forming properties of it. When this alloy was reheated to 580 °C with a heating rate of 20 °C/s and held isothermally for 20 s, semisolid slurry without anisotropy in microstructural morphology and forming properties, exhibiting a homogeneous spherical microstructure was obtained.