过共晶Al-18%Si合金受控扩散凝固组织与行为

Microstructure and solidification behavior of Al-18%Si hypereutectic alloy prepared by controlled diffusion solidification

采用受控扩散凝固(CDS)技术制备过共晶Al-18%Si合金,研究其凝固组织随低温母合金温度变化的演变规律和凝固行为本质。结果表明:受控扩散凝固能抑制初生硅相的过度各向异性生长,有效改善合金凝固组织结构。采用适当温度的Al-25%Si合金(800℃)和纯Al(580℃)混合进行受控扩散凝固时,凝固组织中初生硅相分布均匀,无宏观偏析,且其平均尺寸达到42.85μm。当纯Al温度偏低时,凝固组织中初生硅相偏聚严重;当纯Al温度较高时,凝固组织中初生硅相尺寸偏大。分析表明:在受控扩散凝固过程中,固-液界面前沿形成了较小的"成分过冷",初生硅相在过冷区内趋于平界面生长。溶质原子扩散距离的平方与平衡温度成对数关系,温度愈高,扩散愈充分,宏观偏析愈少。

Using the controlled diffusion solidification （CDS） technology, the predetermined hypereutectic Al-18%Si alloy was prepared. The solidification microstructure evolutions of Al-18%Si alloy with the changing temperatures of low-temperature precursor alloy and solidification behavior were investigated. The results show that, the anisotropy growth of primary Si phase is inhibited by the CDS during solidification process, which can effectively improve the solidification microstructure of Al-18%Si alloy. Adopting an appropriate precursor alloys mixing condition, which is Al-25%Si alloy at 800 ℃ and pure Al at 580 ℃, the distribution of primary Si phase is uniformly and the average size of Si phase is 42.85txm in the solidification microstructure. When the temperature of pure A1 is too low, serious segregation of primary Si phase exists in the solidification microstructure, and when the temperature of pure Al is too high, the average size of primary Si phase is large. The analysis results show that, during the little constitutional supercooling forming on the interface of solid-liquid in controlled diffusion solidification process, the primary Si phase tends to planar interface growth. The relationship between diffused distance square of solute and equilibrium temperature is logarithmic, the higher the equilibrium temperature, the more sufficient the solute diffusion, and the less the segregation.