Sintered R-T-B Magnet RH Diffusion via Surface Coating
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Solution Overview
Problem
Existing methods for improving the intrinsic coercivity (HcJ) of sintered R-T-B based magnets at high temperatures are inefficient, particularly in utilizing heavy rare-earth elements, as they often require excessive amounts and lead to decreased remanence (Br), and struggle to effectively diffuse these elements within the magnet.
Innovation Solution
A method involving a heat treatment process with a layer of RLM alloy powder and RH compound powder on the surface of sintered R-T-B based magnets, where the RLM alloy contains at least 50% RL and has a melting point below the heat treatment temperature, allowing efficient diffusion of RH into the magnet while minimizing surface RH amounts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a heavy rare-earth element RH is profusely added to replace light rare-earth element RL in the sintered R-T-B based magnet, then HcJ will increase, but Br will decrease
Solution Approach 1:
The patent applies preliminary action by pre-coating the magnet surface with RH compound powder and reduction auxiliary agent powder before heat treatment. This preliminary preparation enables efficient RH diffusion during subsequent heat treatment, achieving high HcJ with minimal RH content (0.03 to 0.35 mg/mm²) and avoiding Br degradation that would occur with profuse RH addition.
2Reliability
If a heavy rare-earth element RH is profusely added to replace light rare-earth element RL in the sintered R-T-B based magnet, then HcJ will increase, but the amount of rare natural resources will increase
Solution Approach 1:
The patent applies preliminary action by pre-coating the magnet surface with RH compound powder and reduction auxiliary agent powder before heat treatment. This preliminary preparation enables efficient RH diffusion during subsequent heat treatment, achieving high HcJ with minimal RH content (0.03 to 0.35 mg/mm²) and avoiding Br degradation that would occur with profuse RH addition.
Solution Approach 2:
The patent applies parameter changes by optimizing the mass ratio of RLM alloy to RH compound (9.6:0.4 to 5:5) and controlling the heat treatment temperature (equal to or lower than sintering temperature). These parameter optimizations maximize RH diffusion efficiency, reducing the required RH amount to 0.03-0.35 mg/mm², thereby conserving rare natural resources while achieving high HcJ.
3Reliability
If conventional methods are used to diffuse RH into the magnet, then RH can be supplied to the magnet, but the diffusion efficiency is low and excessive RH is required
Solution Approach 1:
The patent applies the intermediary principle by introducing a reduction auxiliary agent (RLM alloy or RH compound) that mediates the diffusion process. The auxiliary agent reduces RH compound to metallic RH in situ during heat treatment, creating a high concentration gradient that drives efficient RH diffusion into the magnet. This intermediary mechanism achieves high diffusion efficiency with minimal RH content (0.03 to 0.35 mg/mm²).
Solution Approach 2:
The patent applies parameter changes by optimizing the mass ratio of RLM alloy to RH compound (9.6:0.4 to 5:5) and controlling the heat treatment temperature (equal to or lower than sintering temperature). These parameter optimizations maximize RH diffusion efficiency, reducing the required RH amount to 0.03-0.35 mg/mm², thereby conserving rare natural resources while achieving high HcJ.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances HcJ to levels comparable to conventional methods using less RH, maintaining high remanence (Br) and reducing the need for excessive heavy rare-earth elements, thus optimizing magnet performance.
Implementation Method 1
by using a powder mixture including a powder of an RM alloy (where M is one, or two or more, selected from among Al, Si, C, P, Ti, and the like) and a powder of an M1M2 alloy (M1 and M2 are one, or two or more, selected from among Al, Si, C, P, Ti, and the like), and an RH oxide, it is possible to partially reduce the RH oxide with the RM alloy or the M1M2 alloy during the heat treatment
Implementation Method 2
it is possible to partially reduce the RH oxide with the RM alloy or the M1M2 alloy during the heat treatment, thus allowing more R to be introduced into the magnet
Data Source
AI summary
A step of, while a powder of an RLM alloy (where RL is Nd and/or Pr; M is one or more elements selected from among Cu, Fe, Ga, Co, Ni and Al) and a powder of an RH compound (where RH is Dy and/or Tb; and the RH compound is one, or two or more, selected from among an RH fluoride, an RH oxide, and an RH oxyfluoride) are present on the surface of a sintered R-T-B based magnet, performing a heat treatment at a sintering temperature of the sintered R-T-B based magnet or lower is included. The RLM alloy contains RL in an amount of 65 at % or more, and the melting point of the RLM alloy is equal to or less than the temperature of the heat treatment. The heat treatment is performed while the RLM alloy powder and the RH compound powder are present on the surface of the sintered R-T-B based magnet at a mass ratio of RLM alloy:RH compound=9.6:0.4 to 5:5.