Semi-solid microstructural evolution of Mg-Zn-Gd magnesium alloy by the SSIMA process

Semi-solid microstructural evolution of extruded Mg-5.5Zn-2Gd-0.6Zr magnesium alloy with different extrusion ratio by the SSIMA process was investigated. It is found that the relationship between the average diameter of α-Mg grains and the isothermal holding time meets the difference between the cube of average grain diameter and initial average grain diameter equal to the coarstning constant K and the isothrmal time t under the condition of the same extrusion ratio. The coarsening rate constant K is decreased with the increase of the extrusion ratio, which reaches 359 μm³/s,289 μm³/s and 266 μm³/s when the extrusion ratio is 10, 15 and 30, respectively. It is also found that the semi-solid isothermal evolution process of the experimental alloy is accelerated with the increase of the extrusion ratio, meanwhile, the roundness and uniformity of α-Mg grains also are improved.