不同Ce含量Fe-6.5%Si合金的組織、有序結構和中溫拉伸塑性

不同Ce含量Fe-6.5%Si合金的組織、有序結構和中溫拉伸塑性Microstructure, Ordered Structure and Warm Tensile Ductility of Fe-6.5%Si Alloy with Various Ce Content

研究了Ce 含量對鑄造態Fe-6.5%Si（質量分數）合金顯微組織、有序結構和中溫拉伸性能的影響，分析了Ce微合金化改善合金塑性的機理。結果表明：Ce含量（質量分數）為150×10-6以下時，合金鑄造組織無明顯變化，Ce含量為210×10-6以上時，鑄造組織明顯細化；Ce元素的添加可大幅度降低合金的有序結構程度，顯著改善中溫拉伸塑性；當Ce含量為62、150和210×10-6時，400 ℃拉伸試樣的平均斷后伸長率由無Ce試樣的7.4%分別升高至10.1、19.3和23.0%；而Ce含量增加至260和790×10-6時，Ce元素在晶界明顯富集導致試樣拉伸斷口呈現沿晶脆斷特征，平均斷后伸長率下降至15.5和14.2%；有效改善Fe-6.5%Si合金塑性的合適Ce含量范圍為150~210×10-6。

Fe–6.5% (mass fraction) Si 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 cerium (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, and 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 ductility effectively of Fe–6.5%Si alloy.

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