Development of semisolid casting for AZ91 and AM50 magnesium alloys

The feasibility of semisolid casting process with AZ91 and AM50 magnesium alloys, which are usually used for hot- and cold-chamber die-casting, was investigated in this work. Two casting methods were examined: direct casting from the melting-stirring unit and billets casting. The billets had been precast with thixotropic properties, and were heated again by an induction furnace before the casting. The apparent viscosity of the semisolid magnesium slurry during continuous cooling was found as a function of the casting temperature. Viscosity tests show that the appropriate casting temperatures in the two-phase region were in the range of 595-575 °C for AZ91 alloy and 620-614 °C for AM50 alloy. At casting temperature of 585 °C, AZ91 exhibited maximum density and the highest standard mechanical properties. AM50 alloy demonstrated the relative poor mechanical properties in the two-phase region. The toleration of heat treatment of semisolid AZ91 alloy with a 1.8-fold increase in the elongation-to-fracture was observed. No significant differences of the densities and the standard mechanical properties of the alloys between direct or billet castings were demonstrated.