The formation of rosette α phase, structural evolution during the reheating and semi-solid casting of AlSi7Mg alloy

The non-dendritic primary phase is required for the production of parts through the semi-solid metal forming process, for which the spherical phase is the most favored. Under the condition of continuous casting with electromagnetic stirring, the primary phase tends to be rosette-like. For AlSi7Mg alloy, there are three possible aspects contributing to the formation of the rosette α phase. The billets can be reheated to their semi-solid state reliably and repeatedly through a two-phase heating procedure using a vertical tube furnace. The workable temperature is around 577–580 °C. For demonstration, the connecting rods for an air compressor were fabricated successfully through the semi-solid forming process using a 350 t high-pressure die casting unit.