研究了Ce含量对铸造态Fe-6.5%Si (质量分数)合金显微组织、有序结构和中温拉伸性能的影响,分析了Ce微合金化改善合金塑性的机理。结果表明,Ce含量在150×10-6以下时,合金铸造组织无明显变化;Ce含量在210×10-6以上时,铸造组织明显细化。Ce的添加可大幅度降低合金的有序程度,显著改善中温拉伸塑性;当Ce含量为62×10-6、150×10-6和210×10-6时,400 ℃拉伸试样的平均断后伸长率由无Ce试样的7.4%分别升高至10.1%、19.3%和23.0%;而Ce含量增加至260×10-6和790×10-6时,Ce在晶界明显富集导致试样拉伸断口呈现沿晶脆断特征,平均断后伸长率下降至15.5%和14.2%。有效改善Fe-6.5%Si合金塑性的合适Ce含量范围为(150~210)×10-6。
Fe-6.5%Si (mass fraction) alloy is an important soft magnetic material due to its excellent magnetic properties. However, the existence of ordered structure in a great amount is the fundamental cause of poor ductility of the alloy, which restricts the application of the alloy seriously. To modify the microstructure and crystal structure of Fe-6.5%Si alloy by rare earth micro-alloying is one of the significant methods to reduce brittleness and improve plastic deformation ability of the alloy. Whereas, there still lack of elaborate studies on order degree reduction mechanism, ductility improvement evaluation and its connections to a varying microstructure, rare earth distribution, etc., caused by rare earth doping, which restricts a deep understanding on rare earth micro-alloying mechanism and its application in this alloy. In this work, influences of Ce content (mass fraction) on microstructure, ordered structures and warm tensile property of the as-cast alloy were investigated, and the ductility improvement mechanism of the alloy caused by Ce micro-alloying was analyzed. The results indicate that, there is no evident variation of as-cast microstructure when Ce content is below 150×10-6, while the obvious microstructure refinement is observed when Ce content exceeds 210×10-6. Ce addition reduces the alloy's order degree significantly and thus improves its warm tensile ductility obviously. Compared with Ce undoped specimens, average tensile elongation to failure at 400 ℃ increases from 7.4% to 10.1%, 19.3% and 23.0% by 62×10-6, 150×10-6 and 210×10-6 Ce doping, respectively. Inter-granular brittle fracture characteristic occurs in fractured tensile specimens due to the obvious Ce enrichment at grain boundary when Ce content increases to 260×10-6 and 790×10-6, hence the average tensile elongation to failure at 400 ℃ reduces to 15.5% and 14.2%. A reasonable Ce content is within the range of (150~210)×10-6 to improve effectively the ductility of Fe-6.5%Si alloy.