EFFECTS OF AS-CAST CRYSTALLINE STRUCTURE AND Cu SEGREGATION ON COERCIVITY OF Sm (Co, Cu, Fe, Mn)_(7.8) PERMANENT MAGNET

Effects of the as-cast crystaline structure and segregation in Cu on the coercivity of Sm(Co, Cu, Fe, Mn)_(7.8) permanent magnets have been investigated. Experimental results showed that the crystalline structure of the ingot is different with different cooling rates. In the equi-axed grain structure, the inner of the grain is deficient in Cu; free Cu concentrates on the grain boundaries, where an amount of high temperature phase of hexagonal structure of Sm_2Co_(17-x)T_x is preserved, resulting in a decrease in the coercivity. In the fine-columnar grain structure, no serious segregation in composition has been observed. Magnets after sintering and solution treatment exhibit the cellular microstructure; precipitated Cu and SmCo_(5-x)T_x phase rich in Cu disperse on the cell-wall. They probably play, in the course of magnetization reversal, the role of pinning the domain wall, hence, giving high coercivity.