旋转磁场对Mg15Al高铝镁合金凝固组织的影响

Effect of Rotating Magnetic Field on Solidification Microstructure of Mg15Al High-aluminium Magnesium Alloys

利用旋转磁场控制Mg15Al二元高铝镁合金凝固过程,以期获得均匀细小的等轴晶,使合金后续的等通道挤压能顺利进行。通过OM、SEM、EDS测试手段研究了旋转磁场对合金凝固组织及溶质分配的影响。结果表明:旋转磁场主要通过与金属液流相互作用引起强烈的旋流而产生搅拌作用来影响合金的温度场与溶质场的分布,故能够显著细化Mg15Al二元高铝镁合金组织中的初晶α-Mg,促进Al在初晶α-Mg中的固溶,但对于在凝固末期才形成的共晶组织而言,由于凝固末期所剩液相形不成有效流动,其形态受旋转磁场影响不大。随励磁电压增大,晶粒细化效果增加,励磁电压为60V时,晶粒细化效果最佳,Al在初晶α-Mg中固溶量最高,励磁电压继续增加,由于磁场感生热增加将弱化二次冷却,使晶粒细化效果下降。

The solidification process of Mg15Al binary magnesium alloy was controlled by the rotating magnetic field （RMF） to obtain even and small equiaxed grains, which make the followed equal channel-angular pressing proceed. The effect of various-strength rotating magnetic field on microstructure and the solute distribution of the Mg15Al binary magnesium alloy was investigated by OM, SEM and EDS. The results show that the distribution of the temperature field and solute field can be obviously improved by the severe fluid flow from the interaction between the RMF and the liquid metal, so the primary phase a-Mg in the as-cast Mgl5AI binary alloy can be refined and the solid solution of aluminium in the primary phase ~a-Mg can be increased by RMF. But the eutectic microstructure has no change by RMF since no effective flow is formed in the end of solidification. The grain refinement increases gradually with the increase of magnetizing voltage. When the magnetizing voltage reaches 60 V, the finest grain and the highest solid solution of aluminium in the primary phase a-Mg can be obtained. But for the magnetizing voltage higher than 60 V, the grain size will decrease partially as the magnetic field-induced heat weakens the secondary cooling