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采用丁二腈水透明模型合金 ,通过实时观察技术对半固态处理过程中的组织形成及演化机理进行了研究。结果表明 ,球晶是由液相形核长大产生的 ,而非由传统形成机制———断裂枝晶钝化控制 ;并且半固态处理过程中剪切速率显著影响球晶的形成和分布。随着搅动速率提高 ,球化率逐步降低 ,当搅动速率足够高时 ,无球化发生 ;同时 ,球化率对搅动速率的突变非常敏感 ,搅动速率的突变容易造成球晶的大量形核生长。
The microstructure and evolution mechanism of semi-solid state during the semi-solid treatment were studied by using real-time observation technique. The results show that the spherulites are formed by the nucleation and growth of the liquid phase, not controlled by the traditional formation mechanism - dendrite deactivation; and the shear rate during semi-solid processing significantly affects the formation and distribution of spherulites. With the agitation rate increasing, the spheroidization rate gradually decreased. When the agitation rate was high enough, no spheroidization occurred. At the same time, the spheroidization rate was very sensitive to the agitation rate mutation. The agitation rate could easily lead to the massive nucleation of spherulites .