采用连续铸造方式制备的梯度材料

介绍了一种采用多流浇注连续铸造方式制备的用作结构件的材料,阐述了这类材料的特点及其制备实例,最后展望了这类材料的应用前景。     

以连续铸造方法制备梯度材料的实验研究

提出了一种通过双流浇注连续铸造方法生产合金成分随铸件截面连续变化的新型梯度材料的设想。采用自行研制的双流浇注半连续铸造装置的Ａｌ－Ｓｉ二元合金进行了实验研究。实验结果表明：通过调整铸造工艺参数,如浇注温度、内外浇懈的流量比等,可以控制熔体的流动和凝固过程,获得铸件截面上不同的成分梯度分布,合金的力学性能,微观结构和合金成分之间有很好的对应关系。     

稀土在过共晶Al-Si合金中的变质特点

采用金相显微镜、扫描电镜观察了稀土变质的过共晶Ａｌ－Ｓｉ合金中共晶Ｓｉ的形貌。结果表明：稀土在过共晶Ａｌ－Ｓｉ合金中对共晶Ｓｉ的变质不同于稀土在共晶或亚共晶Ａｌ－Ｓｉ合金中的变质作用，即在初晶Ｓｉ周围存在不完全变质组织。产生该组织特征的原因是共晶Ｓｉ在初晶Ｓｉ表面形核生长以及稀土对共晶团中α（Ａｌ）和共晶Ｓｉ两相生长的抑制作用不同。指出了在过共晶Ａｌ－Ｓｉ合金中采用稀土变质时提高冷却速度和使初晶Ｓｉ均匀分布的重要性。     

Derivation of the general equation of the kinetics of phase transformation with nucleation and growth mechanism

The fundamentals of a new method of theoretically studying the kinetics of the phase transformation with nudeation and growth mechanism are demonstrated.Startingfromfinite,heterogeneous system,the survival probability of the individual sites for the given annealing time can be calculated by the present treatment,so that the kinetics equation under general conditions can be derived.In comparison to the classical treatment,the new derivations are not only rigorous and transparent,but also can be used to deal with the non-homogeneous systems and the non-steady process.Also the problems concerning the interference of more than one simultaneously occurring transformations and the correlation between different sites can be studied.