Effects of Processing Parameters on Microstructure and Mechanical Properties of Rheomolded AZ91D Magnesium Alloy

An advanced rheomolder, equipped with a thin-walled phone cover mold, was introduced and used to manufacture the AZ91D magnesium alloy. Effects of different processing parameters including pouring temperature, cylinder temperature and injection velocity on the microstructure and mechanical properties were investigated. The results showed that, with the decrease of pouring temperature or the increase of injection velocity, the size of α1-Mg decreases while the sphericity increases, and the porosity fraction reduces, which raise mechanical properties of rheomolded AZ91D. As the cylinder temperature decreases, the size of α1-Mg decreases and the sphericity increases initially and then remains relatively unchanged while the solid fraction increases continuously. Also, the cylinder temperature has a significant effect on mechanical properties of rheomolded AZ91D and the highest mechanical property is obtained at a cylinder temperature of 555 °C. The optimal rheomolded AZ91D with tensile strength of 273 MPa and elongation of 7.2 % were obtained at the pouring temperature of 600 °C, injection velocity of 2.1 m/s and cylinder temperature of 555 °C. Compared with high pressure die-casting, the tensile strength and elongation were increased by 22.4 and 213 %, respectively.