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 AZ91D-1.2wt%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-21wt%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 AZ91D-0.44wt%MM test bars were produced with addition of extruded Mg-21wt%MM master alloy and the efficiency of alloying was around 80%.