无压浸渗高含量Si/Al复合材料的凝固组织特征

The Solidification Microstructures of High Content Si_p/Al Composite Prepared by Pressureless Infiltration

对用无压浸渗法制备的高含量Si/Al复合材料的浸渗及凝固组织进行了研究,对Si骨架间的凝固组织和浸渗过程中的水淬组织进行了详细的分析,并对2种组织进行了比较。结果表明,Si骨架间的过共晶Al-Si合金液的水淬组织为伪共晶组织,高速率的凝固阻碍了Si的析出和扩散。而在缓慢冷却凝固时,随着初晶Si的析出,形成呈网络状连续的Si相骨架,Si骨架间隙进一步减小,剩余的过共晶成分的液相被分隔局限其间,液相比例减少。在被Si相骨架分隔的微区内产生了类似于离异共晶的析出现象――初晶Si和共晶Si只能沿原预制体Si多孔体骨架上附着析出,凝固后的Al基体为α相,而不是典型的Al-Si共晶组织。另外,Si相的体积分数决定于浸渗温度。

Infiltration and solidification microstructures of high content Sip/Al composites fabricated by pressureless infiltration were investigated in the paper. The water quench microstructure and the solidification microstructures of Si skeleton clearance were compared and analyzed particularly. The results show that the water quench microstructure of Si skeleton clearance is pseudo-eutectic microstructures which is the solidification microstructure of infiltration melt with hypereutectic component of AI-Si alloy. High velocity solidification of melt prevents Si atoms from separating out and diffusing availably. However, when the melt solidified with slow cooling velocity, the residual liquid phase of Si skeleton clearance occupies smaller proportion in whole system for Si skeleton existence. With primary Si separating out, Si skeleton turn into gradually a kind of continuous reticulate structure. The Si skeleton clearance was diminished. The residual liquid phase with hypereutectic component were separated from Si skeleton and surrounding the Si skeleton clearance. In the time, a microstructure similar to the separate-eutectic microstructure occurred in the interspaces of Si skeleton. Namely, the primary Si and the eutectic Si were separated on the surface of Sip porous skeleton under slow cooling conditions. Solidification microstructures was α phase and there were no typical eutectic microstructures in the AI alloys phase of the composites. Furthermore, the Si phase volume fraction depends on the infiltration temperature.