Semi solid metal forming of AlSi7Mg alloy

The non-dendritic primary phase is required for the production of parts thr ough semi-solid metal forming process, and the spheroidal phase is most fav ored. Under the condition of continuous casting with electromagnetic stirri ng, the primary phase tends to be rosette-like. The processing parameters s uch as shear rate, cooling rate, as well as billet withdrawal speed affect the solidification microstructure strongly. For AlSi7Mg alloy, there are th ree possible aspects contributing to the formation of rosette alpha phase. The structural evolution of sample during reheating indicates that, the eut ectic 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 repeatedl y through a two,phase heating procedure using vertical tube furnace. The wo rkable temperature is around 577-580 degreesC. For demonstration, connectin g rods for air compressor were fabricated successfully through semi-solid f orming process using 350 tons high-pressure die casting unit.