R-T-B Sintered Magnet Composition for High Coercivity
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Solution Overview
Problem
R-T-B-based sintered magnets face a challenge in maintaining high coercive force (HcJ) at high temperatures due to irreversible thermal demagnetization, and the use of heavy rare-earth elements like Dy leads to unstable supply and price fluctuations, necessitating a reduction in Dy content while maintaining high residual magnetic flux density (Br).
Innovation Solution
The development of an R-T-B based sintered magnet with a specific composition represented by the formula uRwBxGayCuzAlqM(100-u-w-x-y-z-q)T, where R is composed of light and heavy rare-earth elements, and the inclusion of Ga, Cu, and Al in specific proportions, along with a method involving additional alloy powders and main alloy powders mixed, compacted, and subjected to sintering and heat treatment, to optimize the existence ratio of the R2T14B type compound and reduce the formation of R-T-Ga phase.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If heavy rare-earth elements (Dy) are added to increase coercive force HcJ, then HcJ is improved, but residual magnetic flux density Br decreases and supply stability deteriorates
Solution Approach 1:
The patent changes the compositional parameters by adding Ga (0.2-0.7 mass%), Cu (0.05-0.2 mass%), and Al (0.05-0.5 mass%) to form specific intermetallic phases (R2T17, R6T13M, R-T-Ga) that modify the magnetic properties. This allows achieving high HcJ without relying on heavy rare-earth elements like Dy, thus preventing Br decrease and supply instability
Solution Approach 2:
The patent creates a composite microstructure consisting of multiple phases: main phase (R2T14B), transition metal-rich phase (R6T13M), and intermetallic compounds (R2T17, R-T-Ga). This composite structure enables simultaneous achievement of high coercive force and residual magnetic flux density by distributing different functions across different phases
2Strength
If the amount of R is increased and B is decreased to form R2T17 phase, then coercive force HcJ is improved, but the existence ratio of main phase decreases significantly
Solution Approach 1:
The patent precisely controls the compositional parameters within specific ranges: R (20-30 mass%), T (65-75 mass%), B (7-12 mass%), Ga (0.2-0.7 mass%), Cu (0.05-0.2 mass%), and Al (0.05-0.5 mass%). This parameter optimization ensures sufficient main phase formation while creating enough transition metal-rich phase for high coercive force
Solution Approach 2:
The patent creates local regions with different compositions: the main phase regions provide high saturation magnetization (high Br), while the transition metal-rich phase regions provide high coercivity (high HcJ). This local differentiation allows each phase to optimize its function without compromising the other
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 enables the production of R-T-B based sintered magnets with high Br and HcJ while minimizing the content of Dy or Tb, achieving a balance that maintains magnetic properties without significant decreases in the existence ratio of the main phase.
Implementation Method 1
a compacting step of compacting the mixed alloy powder to obtain a compact
Implementation Method 2
a sintering step of sintering the compact to obtain a sintered body
Implementation Method 3
a heat treatment step of subjecting the sintered body to a heat treatment
Data Source
AI summary
To provide an R-T-B based sintered magnet having high Br and high HcJ while suppressing the content of Dy, and a method for producing the same. Disclosed is an R-T-B based sintered magnet represented by the formula: uRwBxGayCuzAlqMT, where 0.20≤x≤0.70, 0.07≤y≤0.2, 0.05≤z≤0.5, 0≤q≤0.1; v=u−(6α+10β+8γ), where the amount of oxygen (% by mass) is α, the amount of nitrogen (% by mass) is β, and the amount of carbon (% by mass) is γ; when 0.40≤x≤0.70, v and w satisfy the following inequality expressions: 50w−18.5≤v≤50w−14, and −12.5w+38.75≤v≤−62.5w+86.125; and, when 0.20≤x≤0.40, v and w satisfy the following inequality expressions: 50w−18.5≤v≤50w−15.5 and −12.5w+39.125≤v≤−62.5w+86.125, and x satisfy the following inequality expression: −(62.5w+v−81.625)/15+0.5≤x≤−(62.5w+v−81.625)/15+0.8.