The density of the compacted part can achieve more than 95% of theory density after processed sintering process under high vacuum or pure inert atmosphere. Therefore, voids in the sintered magnet are closed which ensured uniformity of magnetic flux density and chemical stability. Since permanent magnetic properties of sintered magnets are closely related to its own microstructure, heat treatment after sintering process is also critical to the adjustment of magnetic performance. SmCo5 magnets are generally sintering at 1120-1140 degrees Celsius for 1-1.5 hours in the argon atmosphere, then slowly cool to 1095-1110 degrees Celsius and maintain for 15-40 mins. Continue slowly cooling to 840-920 degrees Celsius to proceed solution treatment for 0.5-1 hour, then rapidly cool to room temperature. Sm2Co17 magnets possess higher sintering temperature in comparison with SmCo5 magnets. Multistage aging treatment after sintering and solution treatment can be used to regulate the intrinsic coercivity of Sm2Co17 magnets. For sintered Neodymium magnet, Nd-rich phase is serving as the liquid phase which able to promote the reaction and restore surface defects on the main phase grain. Sintering temperature of Nd-Fe-B magnet is commonly at 1050-1180 degrees Celsius. Excessive temperature will lead to grain growth and decrease intrinsic coercivity. In order to obtain ideal intrinsic coercivity, squareness of the demagnetization curve, and high temperature irreversible loss, sintered Neodymium magnet usually needs to process two-stage tempering heat treatment at 900 and 500 degrees Celsius.
