Rare Earth Sintered Magnet Core-Shell Structure
Solution Overview
Problem
Conventional rare earth sintered magnets do not achieve a balanced improvement in residual magnetic flux density (Br) and coercive force (HcJ), limiting their magnetic properties and efficiency in applications such as motors and automobiles.
Innovation Solution
A rare earth sintered magnet with a core-shell structure, where the shell is composed of a heavy rare earth element-rich layer surrounding a light rare earth element-rich core, and includes a Zr compound in the grain boundary phase, along with specific elemental compositions and heat treatment processes to enhance magnetic properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If grain boundary diffusion of heavy rare earth elements (Dy, Tb) is applied, then coercive force (HcJ) is improved, but residual magnetic flux density (Br) deteriorates
Solution Approach 1:
The invention applies local quality by creating a core-shell structure where the shell region (50-500 nm thick) has high heavy rare earth element concentration for coercive force enhancement, while the core region maintains light rare earth element composition for high residual magnetic flux density. This spatial differentiation of material properties resolves the contradiction between improving HcJ and maintaining Br.
Solution Approach 2:
The magnet grain is segmented into two distinct regions: a core and a shell. The shell is formed by selective diffusion of heavy rare earth elements to the grain boundaries, creating a compositional gradient. This segmentation allows different regions to fulfill different magnetic property requirements simultaneously.
2Force
If 2-alloy process with Dy-enriched alloy is used, then coercive force (HcJ) is improved, but manufacturing complexity increases
Solution Approach 1:
Zirconium (Zr) is added to the base alloy composition before sintering, which preliminarily prepares the system for subsequent heavy rare earth element diffusion. The Zr forms intermetallic compounds that act as diffusion pathways, enabling controlled shell formation during heat treatment without requiring complex multi-step alloying processes.
Solution Approach 2:
The invention changes the chemical composition parameter by adding Zr (0.03-0.25 mass%) to the R-T-B system, which fundamentally alters the diffusion behavior of heavy rare earth elements during heat treatment. This compositional parameter change enables simplified single-alloy processing while achieving the desired core-shell structure.
3Force
If shell thickness is increased to improve coercive force, then HcJ is improved, but Br deteriorates
Solution Approach 1:
The invention optimizes the shell thickness parameter within a specific range (50-500 nm) to balance the competing requirements. This precise parameter control ensures sufficient heavy rare earth element concentration at grain boundaries for coercive force enhancement while limiting the volume fraction of the shell to maintain high residual magnetic flux density in the core region.
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 magnet achieves higher Br and HcJ levels, enabling improved energy conversion efficiency and allowing for downsizing and weight reduction in motors, leading to better fuel efficiency and cost savings in automobiles.
Implementation Method 1
a Zr compound is present in a grain boundary phase of the group of main phase grains and/or the shell
Data Source
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AI summary
Provided is a rare earth sintered magnet 10 comprising a group of main phase grains 2 each composed of an R-T-B-based rare earth magnet comprising a core 4 and a shell 6 covering the core 4, wherein a thickness of the shell 6 is 500 nm or less, R includes a light rare earth element and a heavy rare earth element, and a Zr compound 8 is present in a grain boundary phase 7 of the group of main phase grains 2 and/or the shell 6. Also provided are a motor comprising the rare earth sintered magnet 10 and an automobile comprising the motor.