How to improve the magnetic energy product of SmCo permanent magnet
High energy product permanent magnet can promote the miniaturization and high efficiency of motor, information and other fields. Sm2Co17 based sintered permanent magnets have attracted much attention due to their unique high temperature magnetic properties, excellent magnetic stability, excellent oxidation resistance and corrosion resistance.
At present, Nd-Dy-Fe-B permanent magnets are widely used at 150 ° C. However, when the working temperature rises to 200 ° C, in order to maintain the performance of the permanent magnet, it is necessary to greatly increase the use of rare earth Dy, resulting in the increase of manufacturing cost. Therefore, the development of high energy product permanent magnets with excellent temperature stability and zero heavy rare earth has become an important research topic.
The maximum energy product of SmCo permanent magnet with high energy product can reach 35mgoe, and the maximum operating temperature can reach 500 ° C and above. The microstructure of Sm2Co17 based sintered permanent magnet is a kind of cellular structure, in which the cell is a rhombic shape with long axis along the easy magnetization axis. The main phase of SM2 (CO, Fe) 17 is Fe rich in cubic system with the size of 50-200 nm. The thin layer of cell wall is Cu rich SM (CO, Cu) 5 phase in hexagonal system with the thickness of 5-20 nm.
How to improve the magnetic energy product of SmCo permanent magnet?
The theoretical value of the maximum energy product of permanent magnetic material is directly proportional to the square of its saturation magnetization. The first condition to increase the magnetic energy product of permanent magnet is to increase the saturation magnetization of magnet. Only high saturation magnetization can get high remanence and high magnetic energy product. And the magnetic energy product is the structure sensitive quantity. Therefore, it is necessary to optimize the cellular structure of the magnet while increasing the saturation magnetization.
The saturation magnetization and magnetic energy product of SmCo magnets can be effectively improved by optimizing the composition and adjusting the microstructure of SmCo magnets with corresponding heat treatment process. Fe in the main phase of rhombohedral structure is the most important factor. The saturation magnetic polarization (JS) of Sm2Co17 phase is about 12kgs, which increases gradually with the addition of Fe. When Fe increases to the proportion of SM2 (co0.7, fe0.3) 17, JS reaches 16.3kgs. However, when the content of Fe in the magnet is more than 25%, the cellular structure will increase abnormally and the size will exceed 150 nm. Too large cellular structure is not conducive to the uniformity of cellular structure and leads to the sharp deterioration of coercivity and demagnetization curve squareness.
Recent studies have shown that the magnetic properties of magnets can be optimized by optimizing the heat treatment process and adding additional heat treatment links. Appropriate solution temperature can optimize the phase composition of the quenched alloy, thus improving the BR and intrinsic coercivity Hcj of the magnet. When the solution temperature is 1423k, the magnetic properties of the magnet are: br = 12.22kgs, Hcj = 12.7koe. Subsequently, the Hcj of the magnet can be increased to 18.6koe by adjusting the Zr content in the magnet. On the other hand, the introduction of pre aging process can promote the uniform distribution of Cu in the quenched alloy, refine the cellular structure size and improve the squareness of the magnet. The maximum magnetic energy product of the magnet increases from 31.5mgoe to 33.4mgoe. It is also reported that the multi-stage solid solution process can improve the squareness of the magnet and make the maximum magnetic energy product of the magnet reach 35.4 mgoe.
Source: China Permanent Magnet Manufacturer www.ymagnet.com