HREE-free hot-pressed NdFeB magnets represent an important technical route for reducing heavy rare-earth content in NdFeB permanent magnet materials.
Principle of HREE-Free Hot-Pressed NdFeB Magnets
Hot-pressed magnets achieve high coercivity through nanocrystalline grain refinement strengthening. By optimizing the grain-boundary phase (e.g., adding trace amounts of non-rare-earth elements) to block the propagation of reverse magnetization domains, they can eliminate dependence on heavy-rare-earth “grain boundary diffusion,” enabling production with no heavy rare earths or extremely low heavy-rare-earth content.
Process For HREE-Free Hot-Pressed NdFeB Magnets
A two-step “melt-spinning + hot pressing + hot deformation” approach is adopted. First, nanocrystalline melt-spun ribbons are prepared by melt-spinning and crushed into magnetic powder; then hot pressing is performed under vacuum or an inert atmosphere for densification, forming isotropic magnets; finally, hot deformation and plastic flow align the grains along the C-axis, producing highly textured anisotropic magnets.
Advantages of HREE-Free Hot-Pressed NdFeB Magnets
| Low heavy rare-earth dependence: High coercivity is achieved through nanocrystalline grain refinement strengthening and grain boundary optimization, greatly reducing or eliminating the addition of expensive heavy rare earths (Dy, Tb), effectively avoiding supply chain risks from heavy rare-earth resource scarcity, price volatility, and export controls, while significantly lowering overall material costs.
| Magnetic performance: The hot-pressing/hot-deformation process yields magnets approaching theoretical density with few internal pores and more uniform magnetic performance distribution. The magnet rings have smooth torque, making them suitable for low-cogging-torque applications. The nanocrystalline fine-grained structure provides high coercivity, low magnetic flux loss at high temperatures, and low irreversible demagnetization rate, offering temperature stability superior to some traditional low-heavy-rare-earth magnets.
| Corrosion resistance: With high density and uniform grain boundary phase distribution, the magnets effectively block corrosive media. Some products can be used directly without complex surface coatings, reducing post-processing costs.
Limitations of HREE-Free Hot-Pressed NdFeB Magnets
| Shape limitations: Due to the forming characteristics of the hot-pressing/hot-deformation process, hot-pressed magnets are currently mainly limited to ring shapes, making it difficult to produce square, special-shaped, or large-size magnets, which considerably restricts their range of applications.
| High cost: The hot-pressing/hot-deformation process demands extremely high control precision over temperature, pressure, and deformation rate. The equipment is expensive, and the process window is narrow, resulting in relatively low mass-production yield and significantly higher unit manufacturing costs than mature sintered NdFeB magnets.
Magnets Manufacturer
At Tengye, we’re thrilled to be early participants in your new projects. Our passion for magnets extends from material selection and design optimization to providing magnetic solutions. We hope to bring our knowledge and experience to the forefront by actively engaging in your upcoming projects. Work with our magnet experts to get the right magnet solution.
Image Source: Bomatec & Mdpi & Sciencedirect & Spnerkeji & Springer
