R-T-B Sintered Magnet Core-Shell Structure Adhesion
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Solution Overview
Problem
Conventional R-T-B based permanent magnets face challenges with low corrosion resistance due to easy oxidation of rare earth elements and low adhesion strength between the magnet body and protection films, leading to deterioration of magnetic properties and peeling of protection films during use.
Innovation Solution
A R-T-B based sintered magnet with a core-shell structure is developed, where Ce is selectively distributed in the core and R1 (another rare earth element) in the shell, enhancing coercivity and adhesion strength to plated layers by adjusting the mass concentration ratio between Ce and R1 in the core and shell portions, and using Ce's high wettability to improve compatibility with Ni for high adhesion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If Ce is added to R-T-B based magnet to improve adhesion strength and reduce cost, then adhesion strength to plated layer is improved, but coercivity is reduced
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where Ce is concentrated in the core region (providing high adhesion strength where it contacts the plated layer) while R1 is concentrated in the shell region (maintaining high coercivity at the grain boundaries). This spatial differentiation allows each element to perform its optimal function without interfering with the other's properties.
Solution Approach 2:
The patent segments the magnet's microstructure into distinct core and shell regions within each grain. The core contains Ce-rich composition for adhesion, while the shell contains R1-rich composition for magnetic performance. This segmentation resolves the contradiction by assigning different compositional characteristics to different spatial zones of the same grain.
2Reliability
If R-T-B based magnet uses valuable rare earth elements like Nd or Pr to achieve good magnetic properties, then magnetic properties are improved, but material cost increases and resource efficiency decreases
Solution Approach 1:
The patent changes the compositional parameters by replacing some of the valuable rare earth elements (Nd or Pr) with Ce in the core region, while maintaining adequate amounts of R1 in the shell region. This parameter adjustment reduces material cost and improves resource efficiency while preserving magnetic properties through the optimized core-shell structure.
Solution Approach 2:
The patent substitutes expensive rare earth elements (Nd, Pr) with cheaper Ce in the core region where the primary function is adhesion rather than magnetic performance. This substitution reduces material cost while the shell region's R1 content ensures magnetic properties are maintained, effectively using each element where it provides the best cost-performance ratio.
3Reliability
If R-T-B based magnet uses conventional composition to achieve high coercivity, then coercivity is improved, but adhesion strength to protection film is low causing film peeling
Solution Approach 1:
The patent applies local quality by concentrating Ce in the core region where it provides excellent adhesion strength to the plated protection film through its high wettability, while maintaining R1 in the shell region to preserve high coercivity. This localized distribution allows the magnet to simultaneously achieve both high coercivity and strong film adhesion without compromise.
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
The approach results in a magnet with improved coercivity and adhesion strength to plated layers, reducing the risk of film peeling and maintaining high magnetic properties, while efficiently utilizing abundant Ce resources.
Implementation Method 1
Ce has the lowest melting point among the rare earth elements and exhibits high wettability to metals. By using Ce, the adhesion strength to plated layer can be improved.
Data Source
AI summary
The present invention provides a permanent magnet with excellent adhesion strength with plated layer and without significant decrease in magnetic properties, compared to the conventional R-T-B based magnet. By means that the R-T-B based magnet as the raw material is applied to heating treatment for a long time, the major phase grains will form core-shell like structures in the R-T-B based magnet in which R1 and Ce are included as an essential of R. When the mass concentration of R1 and Ce in the core portion is set as αR1 and αCe respectively and that of R1 and Ce in the shell portion is set as βR1 and βCe respectively, the ratio (B/A) between the mass concentration ratio of R1 to Ce in the shell portion (βR1/βCe=B) and that of R1 to Ce in the core portion (αR1/αCe=A) is 1.1 or more.