The effects of thermal gradient and magnetic field on the anisotropy and microstructure of direct cast Nd24Co20Fe41B11Al4 magnets

The NdFeB magnets with millimeter sizes, typically between 0.5 and 12 mm, have been widely used in electronics, acoustic products, and micro-motor. Preparing these magnets by the traditional sintering and bonding techniques is associated with complicated process and sacrificed density and machinability of the magnet. Aiming at the huge market requirements and facing those technical problems, the direct casting is considered to be a simple and low cost alternative technique and has been introduced to make fully dense small size NdFeB magnets. However, it remains a big challenge to achieve high anisotropy in these cast magnets, as well as to design a high magnetic field along the casting direction. In this work, the authors proposed using thermal gradient and magnetic field during the injection casting processes to induce the anisotropy in the 2 mm Nd₂₄Co₂₀Fe₄₁B₁₁Al₄ alloy rod.