(1. 江西理工大学 材料科学与工程学院，赣州 341000； 2. 江西理工大学 机电工程学院，赣州 341000； 3. 江西理工大学 工程研究院，赣州 341000)
摘 要: 利用OM、SEM分析低过热度浇注、双向低频电磁搅拌和稀土元素细化处理复合技术制备的A356-La铝合金铸锭，考察电磁场作用时间恒定时，磁场频率对合金铸锭径向显微组织和稀土元素分布规律的影响，并在最佳工艺参数上探讨熔体搅拌方式对径向组织演化及均匀性的影响。结果表明：磁场频率增加，晶粒球化程度显著，生长方式由枝晶向球晶转变，径向组织以及稀土元素点状弥散分布均匀性增强，磁场频率25 Hz、0.7R时达到最佳，平均等积圆直径和形状因子分别为36.2 μm和0.82；合金径向3个采集点晶粒直径和形状因子的平均值达到41.6 μm和0.76。双向连续搅拌作用于熔体时，组织形貌和均匀性优于单向连续搅拌、双向间歇搅拌。此搅拌方式加快熔体内部质量传输、热量传递进程，一定程度上避免集肤效应对组织均匀性的不利影响。
关键字: 旋转磁场；A356-La合金；稀土元素分布；搅拌方式；凝固组织均匀性
（1. School of Materials Science and Engineering, Jiangxi University of Science and Technology, Ganzhou 341000, China; 2. School of Mechanical and Electrical Engineering, Jiangxi University of Science and Technology, Ganzhou 341000, China; 3. Institute of Engineering and Research, Jiangxi University of Science and Technology, Ganzhou 341000, China）
Abstract:A356-La aluminum alloy ingot prepared by composite technology of low superheat pouring, two-way low-frequency electromagnetic stirring and rare earth element refinement were analyzed by OM and SEM, which contains the microstructure with fine size and round shape primary phase. The influence of magnetic field frequency on the radial microstructure and distribution of rare earth elements in alloy ingot was investigated, when the stirring time of electromagnetic field was constant. The results indicate that when the frequency of magnetic field increases, the degree of grain spheroidization becomes significantly better. The growth mode of grain changes from dendrite grain to globular grain, and the distribution of microstructure along the radial and rare earth element becomes uniform. When the magnetic field frequency is 25 Hz and the radius is 0.7R, the morphology of the primary phase can reach at optimum. The average equal-area circle diameter and shape factor of the primary phase are 36.2 μm and 0.82, respectively. The average primary phase diameter and shape factor from the three collecting points in the radial direction are 41.6 μm and 0.76, respectively. In addition, the influence of melt stirring ways on the evolution and uniformity of microstructure along the radial was discussed under the optimum technological parameters. It indicates that the morphology and uniformity of the microstructure obtained from the two way continuous stirring are better than the single way continuous stirring and two-way intermittent stirring. This stirring way accelerates the internal mass transfer and heat transfer process of the melt, and then, to a certain extent, the adverse effect of skin effect on uniformity of solidification structure can be avoided.
Key words: rotating magnetic field; A356-La alloy; distribution of rare earth elements; stirring method; solidification microstructure uniformity
