Physical Properties of Sintered Neodymium

Mechanical Properties of Sintered Neodymium

Sintered neodymium magnets typically exhibit intergranular fracture characteristics. Their mechanical behavior is primarily determined by a complex multiphase microstructure, which is also influenced by alloy composition, processing parameters, and structural defects such as pores, large grains, and dislocations. In general, a lower total rare-earth content leads to poorer mechanical performance. The toughness of the magnets can be improved by adding low-melting-point metals such as Cu and Ga, which help optimize the distribution of grain boundary phases. Additionally, the inclusion of high-melting-point elements like Zr, Nb, and Ti can promote the formation of precipitates at the grain boundaries, refine grain size, and suppress crack propagation—thus enhancing both strength and toughness. However, excessive addition of high-melting-point metals can result in overly hard magnetic materials, significantly reducing machining efficiency.

Thermal Properties of Sintered Neodymium

Key thermal performance indicators of sintered neodymium include thermal conductivity, specific heat capacity, and thermal expansion coefficient.

The magnetic properties of sintered neodymium gradually degrade as temperature increases. Therefore, the thermal rise in permanent magnet motors becomes a critical factor affecting their ability to operate continuously under load. Good thermal conductivity and heat dissipation are essential to prevent overheating and ensure reliable operation.

Sintered neodymium magnets are easily magnetized along a specific axis (the easy axis), and tend to expand when heated in this direction. However, they may contract when heated along the other two hard magnetization axes—a phenomenon known as negative thermal expansion. This anisotropic thermal expansion can lead to cracking during the sintering process. Furthermore, in permanent magnet motors, sintered neodymium is often combined with soft magnetic structural materials, and the mismatch in thermal expansion between the two can affect dimensional compatibility after thermal cycling.

Electrical Properties of Sintered Neodymium

In the alternating electromagnetic environment of a rotating permanent magnet motor, sintered neodymium magnets can experience eddy current losses, leading to temperature rise. Since eddy current loss is inversely proportional to electrical resistivity, improving the resistivity of sintered neodymium magnets is an effective way to reduce both eddy current losses and the resulting temperature increase. An ideal high-resistivity magnetic material structure involves raising the electrochemical potential of the rare-earth-rich phases to form insulating boundary layers that block electron transport. This results in the grain boundaries being coated or separated from the main magnetic grains by high-resistivity phases, thereby increasing the overall resistivity of the sintered neodymium magnet.