Study On 1:7 Type SmCo Permanent Magnets

Recently, for the application of national defence and military technology hard magnetic materials are required to be worked over 400℃. 1:7 type SmCo permanent magnets is studied frequently material because of its high magnetic properties, high curie temperature, low temperature coefficient of remanence, good anti-corrosion and temperature stability.In this paper some different alloys were designed. The effects of Ag element and Ti element addition on the magnetic properties and heat treatment process of 1:7 SmCo bonded magnets were studied.The effects of the substitution of Ag for Cu or Ti for Zr on intrinsic coercivity of 1:7 SmCo type alloys were studied by using NIM-2000 B-H instrument, scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). It is found that most Ag element in the alloy combines with Cu and Sm to form a Ag-rich phase. The Ag-rich phase never solutes during the heat treatment process. When Ag content increases, intrinsic coercivity of bonded magnet decreases very quickly. Intrinsic coercivity can not be improved effectively with aging when Ag entirely substitutes for Cu. While the content of Ti increases, intrinsic coercivity of bonded magnet also decreases very quickly in the Ti addition alloy. With the conent of Ti increasing, the dropping trend becomes smoothly. When Ti entirely substitutes for Zr, intrinsic coercivity of bonded magnet is 53.1% of the alloy without Ti.The microstructure and phase of 1:7 type SmCo alloy during heat treatment process were determined by using x-ray diffraction analysis (XRD) and microscope. Before heat treatment, 2:17 phase and can be found in the alloy, while a few 1:5 phase also exists. After solid solution, 1:5 phase and 2:17 phase solutes completely, and form supersaturated solution,only 1:7 phase (a 1:7 composition is Sm7Co49, corresponding to a stacking of two Sm2Co17 and three SmCo5 unit cells, for simplicity we will keep the popular notation Sm(Co, Cu, Ti)7) can be observed in the alloy. After the whole heat treatment, 1:7 phase decomposes into two phases: a nearly stoichiometric 1:5 grain-boundary phase, crystallizing in the CaCu5 structure, and a main 2:17 phase, very likely having the rhombohedral Th2Zn17 structure.At last, the effect of heat treatment process on the intrinsic coercivity of 1:7 SmCo alloys was studied.It shows the optimum heat treatment process depends on the composition of alloys.The most optimum heat treatment processes of four typical 1:7 SmCo alloys were achieved. Also their magnetic properties were achieved.