熔体温度处理细化亚共晶Al-Si合金组织

利用正交试验的方法对熔体温度处理细化亚共晶Al-Si合金的凝固组织进行了研究，结果表明，经过熔体温度处理后，凝固组织中一次枝晶尺寸明显减小，长的树枝晶变为短的树枝晶或等轴晶，并且枝晶数量明显增多；二次枝晶臂间距变化不明显，从原子团簇的角度分析认为，这是由于高，低温熔体混合后，低温熔体中大的原子团簇得到细化，从而导致混合熔体中形核质点增殖的结果，研究同时发现，高，低温熔体的混合方式对熔体温度处理效果有直接影响，熔体的均匀混合有利于增大熔体凝固过冷度，减小临界晶核半径，促进凝固组织的细化。

Solidification Structure of Hypoeutectic Al-Si Alloy Refined by Melt Thermal Treatment

The solidification structure which is refined by the melt thermal treatment (MTT) process was studied with orthogonal experiment. The results show that the first dendrite size (FDS) reduces obviously, and the long dendrites turn into short ones or equiaxed grains and the amount of the dendrites increases. However, the second dendrite arm spacing (SDAS) changes little. This is resulted from the multiplication of the original nucleates or clusters in the low temperature melt. And the mixing mode of high and low temperature melts play an important role in the MTT process. The multi hole mode is more beneficial than the mono hole one to make the mixing melt homogeneously, to increase the melt solidifying undercooling, reducing the critical nucleate radius, and so the solidification structure is refined best.