Hard Magnetic Alloy Vacuum Sintering

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Most of the parts made of hard magnetic alloys are formed by powder metallurgy, and then solution treatment or annealing is carried out. Therefore, the heat treatment of hard magnetic material workpieces is mainly vacuum sintering, vacuum solution treatment and vacuum annealing. Due to the strict control of carbon content for NdFeB and AlNiCo alloy materials, whether the hard magnetic alloy parts are sintered or solution treated, the heating elements and reflective screens of the vacuum furnace should be made of molybdenum sheets.

The hard magnetic alloy parts are punched or extruded in the mold after mixing the powder and the binder uniformly. During the sintering process, due to the presence of the binder, the workpiece will have a peak of outgassing between 300 and 600°C, and a second peak of outgassing will appear between 900 and 1000°C. Therefore, the vacuum furnace used for hard magnetic alloy sintering should be equipped with a diffusion pump with a large pumping speed to avoid oxidation.

After sintering and forming of hard magnetic alloy parts, some need to undergo solution treatment to make the composition of the material uniform and the structure stable, so as to improve its permanent magnetism. Since the solution treatment has certain requirements on the cooling rate (>100℃/min), the molybdenum sheet type pressurized gas quenching furnace can be used for the solution treatment.

Process flow:

NdFeB ingots are smelted into NdFeB ingots under the protection of Ar gas in a rotary vane vacuum smelting furnace. The ingot is roughly crushed, disc milled, and air milled into alloy powder with an average particle size of 3.5-4.1 μm. The powder is prepared under the protection of N2 gas, and 0.10%-0.65% of antioxidants and lubricants are added. The powder was oriented in a magnetic field of 1600 kA/m and formed by isostatic pressing with a vertical steel die. The pressed blanks were sintered under the vacuum condition of 10-3～10-2Pa, the sintering temperature was 1080℃, 1090℃, 1100℃, 1110℃ respectively, and air quenched and cooled after holding for 3h. Adopt secondary tempering, first tempering at 950℃ for 2.5h, and then tempering at 560℃ for 2h.

The use of vacuum heat treatment technology for magnetic materials has extremely obvious advantages in improving the quality of parts, reducing production costs, and improving the production environment, so it is a technology worthy of promotion and long-term research.

Equipment selection: The RVS vacuum sintering furnace provided by SIMUWU is an excellent product for processing this kind of process. It has the characteristics of good temperature uniformity and high temperature control accuracy. SIMUWU provides a professional team of engineers who can solve various problems encountered in the production process and are committed to giving customers the most convenient and efficient experience.