SEMI–SOLID A356 ALLOY SLURRY PREPARED BY A NEW PROCESS

Because of the solidifying characteristic of alloy and the difference in thermal conductivity of mould, the microstructures of different zones of semi–solid slurry are different, which is hard to satisfy the requirement of rheoforming. A new process preparing semi–solid slurry is proposed, in which a locally rapid cooling near the center zone of mould can be realized by inserting a copper rod into the slurry and then pulling out repeatedly, except application of a weakly electromagnetic stirring. Semi–solid A356 alloy slurry was prepared by the new process and the effects of the new process on morphology and size of primary α–Al in semi–solid A356 were researched. The results indicate that the nucleation rate, morphology and grain size of primary α–Al are markedly improved by the new process. Primary α–Al with small size presents particle–like or globular–like and distributes uniformly in the slurry even at lower overheating. The grain refining and structural homogeneity are relative to homogenization of the temperature field in the mould.