Optimization of rapidly quenched Co–Zr and (Co,Fe)–Zr alloys for rare earth free permanent magnets

Abstract

To develop rare earth free permanent magnets, the compositions of rapidly quenched binary Co–Zr alloys and Fe substituted Co–Zr alloys were optimized. The Co100-xZrx alloys with x = 16–18 show good combination of hard magnetic properties. The highest coercivity of 3019 Oe was obtained at x = 18 and the highest maximum magnetic energy product of 4.97 MGOe was obtained at x = 17. In the Co82-yZr18Fey (y = 0–8) alloys. Fe substitution decreased the coercivity but slightly increased the saturation magnetization. 8 at.% Fe substitution can increase the Curie temperature to 785 K. All alloys show high thermal stability of magnetic properties. The temperature coefficient of coercivity in the range of 300–400 K for Co82-yZr18Fey (y = 0 and 4) alloys are both about ~0.1%/K, which is significantly lower than that of Nd-Fe-B alloys. In addition, Co–Zr based alloys exhibit excellent corrosion resistance and Fe substitution can further reduce the corrosion tendency in NaCl solution.