大规格ZK60镁合金坯料半连续铸造工艺研究

Semi-continuous Casting for Large-scale ZK60 Magnesium Alloy Ingots

采用半连续铸造工艺制备了500mm的大规格ZK60镁合金坯料。采用多次低压转注移液和静置技术净化镁合金熔体,分析了工艺参数对坯料冶金质量的影响,确定了合理的工艺参数区间,并对镁合金铸锭的主要冶金缺陷的形成机制及组织特征进行了研究。结果表明,铸造速度过大或二次冷却水的流量过大导致铸锭中心附近形成通心裂纹缺陷。大规格ZK60镁合金半连续铸锭的显微组织为α-Mg基体和MgZn2相,MgZn2相在晶界上不连续析出,铸锭的径向组织不均匀,边缘处的晶粒尺寸明显小于中心处的。

ZK60 magnesium alloy ingots with the diameter of 500 mm were fabricated by the semi-continuous casting.The melt was well purified by low pressure transferring the melt and standing technique.The effects of the casting parameters on the metallurgy quality of the ingots were investigated and the reasonable parameter windows were established.The metallurgy defects were analyzed to understand the formation mechanism of the defect.The characteristics of the microstructure was also observed.The results reveal that the casting velocity has the significant effect on the metallurgy quality of the ingot.The through-crack can be formed in the center zone of the ingot in case of using the higher velocity or the higher water flow.The microstructure of the large-scale ZK60 magnesium alloy is composed of equiaxed grain withα-Mg matrix and the second phases MgZn2 which are precipitated in the grain and the grain boundary discontinuously.The grain in the edge of the ingots is much more refined than that of the center of the ingots.