近液相线半连续铸造A356铝合金显微组织

采用近液相线半连续铸造法制备铸造A356铝合金，获得金属半固态加工要求的细小，等轴的“非枝晶”组织，研究了铸造温度、保温时间及冷却速度对该组织的影响规律。结果表明，在液相线附近，降低铸造温度，有利于减小晶粒尺寸；晶粒平均等积圆直径最小可达42．6μm，初始固相体积分数最多可达98．4％，同一温度下，晶粒尺寸随保温时间的延长而粗化；冷却速度快，晶粒尺寸细小；同一铸锭，其中心部位的组织比边缘部位的组织粗大，且分布均匀、等轴特征明显。

MICROSTRUCTURE OF NEARBY LIQUIDUS SEMI-CONTINUOUS CASTING ALUMINUM ALLOY A356

The microstructure of aluminum alloy A356 with fine equiaxed nondendritic grains was obtained by means of nearby liquidus semi-continuous casting method, which is needed by semisolid metal process. The influences of casting temperature, heat preservation time and cooling rate on nearby liquidus casting microstructure are investigated. The results show that in the nearby of liquidus, the grains size becomes tiny with reducing of casting temperature, the least average equal- area circle grain diameter is 42.6 um, and the original solid fraction may reach 98.4%. Prolonging the heat preservation time makes grain size coarse at the same temperature, and increasing the cooling rate makes grain size fine. The microstructure of ingot cast in the Fe-mould is finer than that in the graphite-mould. The grains size of ingot middle is coarser, more even and equiaxed than that at the edge of ingot in the same ingot cast.