Effects of copper and zirconium contents on microstructure and magnetic properties of Sm(Co,Fe,Cu,Zr)z magnets with high iron content

Abstract

The evolution of the microstructure, microchemistry and magnetic properties of the Sm(CobalFe0.28CuyZrx)7.6 magnets with different Zr and Cu contents was investigated. It is found that the coercivity of the Sm(Co,Fe,Cu,Zr)z magnets is sensitive to Zr content. The deficiency of Zr content causes heterogeneity of Cu and Fe distributions, while an excessive Zr content leads to the formation of a SmCoZr impurity phase. The cellular structure and distribution of Cu concentration gradient between the cell boundary phase and cell phase are destroyed by inappropriate Zr content, which results in a reduction of coercivity. The Cu concentration difference between the cell boundary phase and cell phase increases with increasing Cu content. The coercivity of the Sm(CobalFe0.28CuyZr0.02)7.6 magnets increases from 10.4 to 25.4 kOe for y = 0.05 and y = 0.07. However, the excess of Cu element destroys the cell boundary phase and enlarges the cell size, resulting in a significant decrease of squareness and energy density. The optimum performance (remanence of 11.4 kG, coercivity of 25.4 kOe, maximum magnetic energy product of 30.4 MGOe) was obtained for the Sm(Co0.63Fe0.28Cu0.07Zr0.02)7.6 magnet.