液相线铸造法非枝晶半固态组织形成机理探讨

对液相线铸造铝合金形核机理和晶粒长大机制进行了理论分析，提出了液相线铸造形核机理，在小的过冷过度，大量的原子团簇瞬态发展成为晶核，形核数目多且均匀，有利于晶粒在互相抵触之前均呈球形长大，晶粒的长大分为三个阶段，球形长大，枝晶长大和枝晶抵触后枝晶的熟化，重点推导了晶粒球形大长的稳定性判据，即不稳定因子，在凝固的初期，降低冷却强度有利于增大不稳定因子，从而利用球形晶粒的获得，在凝固的中后期，增加冷却强度，有利于保存获得的球形晶粒。

DISCUSSION ON THE FORMATION MECHANISM OF NONDENDRITIC SEMISOLID MICROSTRUCTURES DURING LIQUIDUS CASTING

The mechanisms of the grain nucleating and growing in Al alloys cast by liquidus casting were analysed theoretically. The nucleating mechanism can be discribed as follow: atom clusters with some solid properties form firstly and are developed instantaneously to nucleus in the melt under small super cooling. These nucleus are distributed uniformly and have big amount, which are favorable to the global growth of the grains before their collision. The growth of grains is divided into three stages: the first is ball-like growth, the second dendritic growth and the last dendritic ripenning after contacting of dendrites. The stable criterion of the global growth of grains, namely the instable factor was deduced. Reducing the cooling rate can increase the instable factor, thus is suitable for the formation of the global grains at beginning of the solidification. In the solidified middle or end enhancing the cooling rate is suitable for preservation of the global grains.