Semi solid metal forming of AlSi7Mg alloy

The non-dendritic primary phase is required for the production of parts through semi-solid metal forming process, and the spheroidal phase is most favored. Under the condition of continuous casting with electromagnetic stirring, the primary phase tends to be rosette-like. The processing parameters such as shear rate, cooling rate, as well as billet withdrawal speed affect the solidification microstructure strongly. For AlSi7Mg alloy, there are three possible aspects contributing to the formation of rosette alpha phase. The structural evolution of sample during reheating indicates that, the eutectic melts only after the Si phase diffuses to some extent. The morphology of Si phase changes from flake to particulate then melts with increase in temperature. The rosette a phase spheroidizes through separation of petals. The billets can be reheated to its semi-solid state reliably and repeatedly through a two,phase heating procedure using vertical tube furnace. The workable temperature is around 577-580 degreesC. For demonstration, connecting rods for air compressor were fabricated successfully through semi-solid forming process using 350 tons high-pressure die casting unit.