Fig. 1b. A solidified steering knuckle is shown after the sand cores have been removed by the ablation solvent.
types hinder the other’s movement to produce neutral buoyancy. Te presence of graphite also makes the alumi- num silicon carbide alloy more machinable and wear resistant, with a lower density. During the solidifi-
cation of a discontinu- ously reinforced MMC, the solidifying alloy interacts with the particulate reinforcement to either push the particles into the last freezing, interdendritic regions or engulf them in the solidified dendrites. Te phenomenon of particle pushing is a hindrance to achieving a uniform dispersion of reinforcements in cast MMCs. In order to improve the dispersion of micro-size particles, the solidification rate must be high enough to promote engulfment of the particles or refine the dendritic microstructure. Ablation has the potential to increase the solidification
rate and provide the required dispersion of the particulate reinforcement in the finished casting. In the process, a core package is made using a proprietary binder. Shortly after the alloy is poured, a liquid or liquid/gas mixture is directed to the core surface. Te ablation media dissociates the binder and erodes the silica sand cores, enabling the ablation media solvent to come in direct contact with the liquid alloy, removing the latent heat of solidification with high cooling rates. As the ablation solvent progressively moves from one end of the casting to the other, it results in rapid unidirectional
图1b 砂芯被消融剂溶 蚀后，可以看到已经凝 固的转向节铸件.
入还能使铝-碳化硅 合金加工性更好， 更耐磨，同时密度 更低。
在非连续强化的 金属基复合材料的 凝固过程中，凝固 的合金与强化颗粒
不断相互作用，或者将颗粒推向最后凝固的树枝晶区 域，枝晶间或者颗粒被凝固的枝晶吞没。颗粒被推挤的 现象会阻碍铸造金属基复合材料中强化相的均匀分布。 为了改善微米级颗粒的均匀分布，凝固速度必须足够 快，以分散颗粒或者细化枝晶组织。
消融铸造法可以加快凝固速度，最终使铸件中的强 化颗粒分布符合要求。在这个过程中，用专利粘结剂制 作了一套组芯。浇注后不久，液态或气液混合物被引致 组芯的表面。消融介质将粘结剂脱掉，并侵蚀石英砂砂 芯，消融介质进一步与合金熔液直接接触，从而通过高 的冷却速度带走凝固潜热。
消融介质逐渐从铸件一端流向另一端，从而带来快速 的单向冷却。在消融铸造方法中，原来凝固较慢的厚截
Fig. 2a. The conventionally cast composite featured silicon carbide in large clusters among the interdendritic regions.
图2a 在采用传统铸造法生产的复合材料中，碳化硅在晶间区域 大量集中.
Fig. 2b. The ablation composite sample exhibited more evenly distribut- ed silicon carbide and graphite particles with a higher volume fraction.
图2b 在消融铸造法复合材料试样中，碳化硅与石墨颗粒体积分 数更大，分布更均匀
Spring 2012
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