复合物理场对AZ61镁合金半连续铸造凝固组织的影响

Effect of Compound Physical Field on Microstructures of Semi-Continuous Cast AZ61 Magnesium Alloy Billets

采取不同外场施加方式进行半连续铸造以制备Φ165 mm AZ61镁合金锭坯,研究不同外场施加方式对AZ61镁合金锭坯晶粒尺寸和硬度的影响。结果表明,施加频率为30 Hz、电流为60 A的交变电磁场后,铸锭边部和中心平均晶粒尺寸由常规半连续铸造(DC)的248和276μm分别降至196和259μm,降低幅度分别达21%和6.2%,边部和中心晶粒细化程度明显不同;而施加超声-低频电磁复合场时,铸锭边部和中心平均晶粒尺寸分别降至185和208μm,降低幅度分别达25.4%和24.6%,中心区域晶粒细化程度大幅度提高。另外,与常规DC铸造相比,复合场铸造使合金铸锭的硬度提高且从铸锭边部到中心硬度差别明显减小。可见,超声场-低频电磁复合场半连续铸造显著改善了AZ61镁合金锭坯的内部质量,使凝固组织更加均匀、细小,硬度提高并分布均匀。

AZ61 magnesium alloy was semi-continuously cast into billets with 165 mm in diameter by different external field application ways. The effects of different external field application ways on the grain size and hardness of AZ61 billets were investigated. The results show that compared with the conventional direct-chill semi-continuous cast billets, the grain size of the AZ61 billets cast declines from 248 μm in the edge and 276 μm in the centre to 196 μm and 259 μm, respectively（with a reduction of 21% and 6.2%, respectively） by low-frequency electromagnetic field（f=30 Hz, I=60 A）. The structure refining effects in edge and centre are significantly diverse. However, the grain size in the edge and centre reduces from 248 μm in the edge and 276 μm in the centre to 185 μm and 208 μm, respectively（with a reduction of 25.4% and 24.6%, respectively） by combining ultrasonic and LFEC, and the structure refining effects in centre are significantly improved. Moreover, compared with the conventional DC casting, the compound physical field can improve the hardness of the ingot and obviously reduce the difference of hardness from edge to centre. Therefore, the compound physical field greatly improves the inner qualities of AZ61 magnesium alloy ingot billet, and the microstructure is markedly refined, so the hardness of ingots is uniformly improved.