Sintered NdFeB Magnet Processing with R-Al-Cu Liquid-Phase Sintering
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Solution Overview
Problem
Existing methods for producing NdFeB-based sintered magnets face challenges such as long pulverization processes, irregular particle shapes, and the formation of oxide films during the reduction-diffusion process, which deteriorate the magnetic properties of the sintered magnets.
Innovation Solution
A method involving the use of an R-Al-Cu powder as a sintering agent, produced by mixing RH2, Al, and Cu powders, agglomerating, and heat-treating them to form a metal alloy, which is then used to improve the sintering of R-Fe-B-based magnet powders, thereby reducing the melting temperature and preventing oxide film formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a reduction-diffusion process is used to produce magnet powder, then uniform fine particles can be produced, but oxide films are formed that make sintering difficult and deteriorate magnetic properties
Solution Approach 1:
The patent applies preliminary action by adding the sintering agent (R-Al-Cu powder) before the sintering process. The sintering agent is mixed with the magnet powder in advance, and during sintering, it melts first to form a liquid phase that facilitates sintering while preventing oxide film formation. This preliminary preparation resolves the contradiction by having the sintering facilitator ready before the sintering difficulty arises.
Solution Approach 2:
The sintering agent acts as an intermediary substance between the oxide-coated magnet powder particles. The R-Al-Cu alloy melts and forms a liquid phase that mediates the sintering process, allowing particles with oxide films to bond effectively. The intermediary liquid phase from the sintering agent enables sintering despite the presence of oxide films that would otherwise prevent direct particle bonding.
2Productivity
If traditional melting and quenching process is used, then magnet powder can be produced, but particle shape is irregular and miniaturization is limited
Solution Approach 1:
The patent applies parameter changes by fundamentally altering the production parameters from high-temperature melting (1500-2000°C) to low-temperature reduction-diffusion process. This parameter change enables production of uniform fine particles with regular shapes while maintaining production efficiency. The change in processing temperature and method parameters resolves the contradiction between productivity and particle shape quality.
3Ease of manufacture
If high temperature sintering is used, then sintering can be achieved, but magnetic properties deteriorate due to oxide film formation and particle decomposition
Solution Approach 1:
The patent applies phase transitions by utilizing the melting of the R-Al-Cu sintering agent to create a liquid phase at relatively low temperatures. This liquid phase enables sintering without requiring high temperatures that would decompose magnetic particles. The phase transition from solid to liquid in the sintering agent facilitates sintering feasibility while the subsequent solidification preserves magnetic properties, resolving the contradiction between sintering feasibility and magnetic property preservation.
Solution Approach 2:
The patent employs an inert atmosphere (vacuum or protective gas) during sintering to prevent oxide film formation. This inert environment protects the magnetic particles from oxidation while the sintering agent facilitates bonding. The combination of inert atmosphere and sintering agent resolves the contradiction by enabling sintering without the harmful effects of high-temperature oxidation.
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 the magnetic properties of the sintered magnets by improving the coercive force and magnetic flux density, reducing production costs, and allowing for larger quantities of high-purity metal alloys to be produced with precise control over composition and temperature.
Implementation Method 1
sintering the mixed powder to form a sintered magnet
Implementation Method 2
the R-Al-Cu powder is an alloy of R, Al and Cu... adding a R-Al-Cu powder as a sintering agent... reducing the melting temperature
Implementation Method 3
producing an R-Fe-B-based magnet powder by a reduction-diffusion method
Implementation Method 4
reduction-diffusion process in which Nd2O3, Fe, and B are mixed and reduced
Implementation Method 5
mixing RH2 powder, Al powder, and Cu powder to form a sintered precursor
Implementation Method 6
raising the temperature of the agglomerated sintered precursor to form a metal alloy
Data Source
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AI summary
The present disclosure relates to a method for producing a sintered magnet and a sintered magnet produced thereby, and the method for producing a sintered magnet includes the steps of: producing an R-Fe-B-based magnet powder by a reduction-diffusion method, adding a R-Al-Cu powder as a sintering agent to the R-Fe-B-based magnet powder to form a mixed powder, and sintering the mixed powder to form a sintered magnet, wherein the R-Al-Cu powder is an alloy of R, Al and Cu, and the R is Nd, Pr, Dy, Tb or Ce.