Effects of Grain Refiner on the Microstructural Evolution during Making Semi-Solid Slurry of the A357 Alloy

The enthalpy equilibration method is a novel technique to produce globular grain structure in semi-solid slurry preparation. In this process, the liquid is firstly poured into a metallic crucible, which possesses low thermal conductivity and high thermal capacity. Homogeneous distribution of temperature within the metallic crucible is achieved by rotating the crucible and cold down to a temperature between liquidus and solidus, determined by the requirement of solid fraction. The semi-solid slurry is then transferred to a high pressure die caster. In order to achieve a spherical microstructure morphologies in the entire slurry, effects of grain refiners, in addition to the enthalpy equilibration method, on the microstructure of the slurries of A357 alloy were investigated. Quantitative metallographic measurements were applied to evaluate microstructural evolution and processing parameters were optimized.