Semi-solid A356 alloy slurry for rheocasting prepared by a new process.

To obtain the semi-solid slurry with uniform and fine structure morphology that satisfies the requirement of rheocasting process, a new process for preparing semi-solid Al alloy slurry was developed, in which local chilling was combined with low superheat pouring and slight electromagnetic stirring (LSPSEMS). Themorphology and the size of primary α-AI in the A356 alloy slurry prepared with the new process, i.e., LSPSEMS with local chilling, were investigated using MIAPS image analyzing software, and the grain refinement mechanismwas discussed. The results indicate that the semi-solid primary phase consists of particle-like or globular-like α-AI, and the morphology and grain size of primary CT-AI in the slurry can be markedly improved by the new process.The fine primary α-AI distributes uniformly in the slurry, which satisfies the requirement of rheocasting. Comparedwith the alloy prepared by LSPSEMS, the average equal-area-circle grain diameter of primary CT-AI in semi-solidA356 alloy ingot prepared by the new process is decreased from 85.6 μm to 68.8 μm at the central area, 112.6pm to 77.6 pm at the transition area and is 84.7 μm in the edge area, respectively. The corresponding shapefactor of primary α-AI is increased from 0.78 to 0.83, 0.54 to 0.77 and 0.28 to 0.59, respectively. In addition, the pouring temperature could be suitably raised from 620-630 °C of the traditional process to 650 °C using this technique, which is convenient for practical operation. The mechanism of grain refinement, in the new process, is that the local chilling quickens up the temperature decrease in the center of the melt. The nuclei could not grow up in a short time so the finer grains are formed in the melt. [ABSTRACT FROM AUTHOR]