RESEARCH ON ALLOYING TECNIQUES OF MISCHMETAL IN DIE CASTING MAGNESIUM ALLOY

An aim of the experiments is to study alloying techniques of dollop-like MM , as-cast and extruded Mg - MM master alloy in die casting AZ91D magnesium alloy at conventional cold chamber die casting temperature. The as-cast AZ 91 D -1.2 wt % MM alloys were prepared and MM was added by different way at 720°C. The results showed that the efficiency of alloying achieved less than 50% within 30 min when dollop-like MM was added. When MM was added by as-cast and extruded Mg -21 wt % MM master alloy, the efficiency of alloying was improved significantly. The microstructure and analytical studies were carried out using optical microscopy and differential scanning calrimetry (DSC). Testing results showed the Mg - MM master alloy could melt easily down at die casting temperature because Mg - RE phases with lower melting point were formed. The grain refining efficiency of the master alloy was improved by extrusion. The improvement could be attributed to the decrease in Mg - RE particle size and increase in the number of nucleating sizes for Mg . Then die-casting AZ 91 D -0.44 wt % MM test bars were produced with addition of extruded Mg -21 wt % MM master alloy and the efficiency of alloying was around 80%.