Research On Compound Processing Of Preparation Of Hypereutectic Al-Si Alloy

Semi-solid metal process has advantage of breaking primary phase. In this article, a mechanical stirring apparatus is designed to produce semi-solid hypereutectic Al-Si alloy billet with tiny primary phase by semi-solid process and modification.Around modification and the main mechanical stirring technology parameters of agitation strength, stirring rate and cooling rate, series of trials are designed to discover the relation between technology parameters and semi-solid microstructure.During solidification, the early growth of the primary crystals of Al-Si alloy slurry continues dendritially. With further vigorous agitation, the dendrite arms gradually bend and merge. Meanwhile, the dendrite arms are melted and/or ruptured into numerous small crystals at the root of arms. As the continuous growth, the primary crystals evolve toward more spherical.As the increasing of mechanical stirring strength, primary phase is spherer and the size of primary silicon decreases. The experiments show that too high cooling rate disadvantages the formation of spherical primary crystals, while higher mechanical stirring strength is necessary to spheroidize and homogenize the primary crystals.There has advantage to obtain short and thick primary silicon and improve process efficiency with P modification in semi-solid metal process. But the modification power of RE is relieved by mechanical stirring, so it is not necessary to add RE as a modifier in semi-solid metal process.The tensile strength of semi-solid metal(SSM) sample is higher 20-30% than that of metal mold sample. Elongance 8 of SSM sample is higher 2.8-4.5% than that of metal mold sample. At the same condition of abrasive wear and tear, SSM sample wear and tear is reduced 8-15% than that of metal mold sample.