R-T-B Alloy Strip Columnar Crystal Control for Magnet Coercivity
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Solution Overview
Problem
The shape and size variation of alloy powder obtained from grinding alloy strips hinders the improvement of magnetic properties in R-T-B based sintered magnets, making it difficult to enhance coercive force and residual flux density effectively.
Innovation Solution
The alloy strip is micronized to reduce variation in columnar crystal shapes and sizes, with specific constraints on the average and maximum lengths of these crystals, and a high percentage of R-rich phases with limited dimensions, resulting in a more homogeneous microstructure and increased coercive force.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional strip casting method is used to produce alloy strip, then production process is simple, but the shape and size variation of alloy powder obtained by grinding is considerable, making it difficult to improve magnetic properties
Solution Approach 1:
The invention changes the cooling rate parameter during strip casting to produce a specific columnar crystal structure. By controlling the cooling rate to be 1000-3000°C/sec, the alloy strip develops columnar crystals with controlled morphology and size distribution, which subsequently yields more uniform alloy powder after grinding, directly addressing the manufacturing precision issue
Solution Approach 2:
The invention creates local quality differences within the alloy strip by forming a specific columnar crystal structure in the thickness direction. This localized structural control ensures that when the strip is ground into powder, the resulting particles have more consistent shapes and sizes, improving magnetic property uniformity without requiring complex equipment
2Reliability
If heavy rare earth metals such as Dy and Tb are used to improve magnetic properties, then coercive force increases, but material cost increases significantly
Solution Approach 1:
The invention replaces expensive heavy rare earth metals (Dy, Tb) with a cost-effective microstructural design approach. By controlling the columnar crystal structure and R-rich phase distribution during strip casting, the patent achieves high coercive force without relying on costly rare earth additives, effectively substituting expensive materials with an engineered structural solution
Solution Approach 2:
The invention creates a composite microstructure consisting of columnar crystals of R2T14B phase with controlled morphology and R-rich phases at grain boundaries. This composite structure, achieved through controlled cooling, provides enhanced coercive force through structural design rather than chemical composition, avoiding the need for expensive heavy rare earth metals
3Reliability
If columnar crystals with large size variation are used in sintered magnet production, then production is easier, but magnetic properties cannot be significantly improved
Solution Approach 1:
The invention changes the cooling rate parameter to 1000-3000°C/sec during strip casting, which controls the nucleation and growth of columnar crystals. This parameter control ensures that the columnar crystals develop with consistent morphology and size distribution, creating a uniform microstructure that yields superior and more consistent magnetic properties in the sintered magnet
Solution Approach 2:
The invention achieves homogeneity in the columnar crystal structure by controlling the solidification process. The resulting alloy strip has uniformly distributed columnar crystals with consistent dimensions, which when ground into powder, produces particles with uniform shapes and sizes. This homogeneity directly translates to improved and more consistent magnetic properties in the final sintered magnet product
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 leads to a significant increase in the coercive force of R-T-B based sintered magnets without using expensive heavy rare earth elements, while maintaining or improving residual flux density, through the production of a more uniform and micronized alloy powder.
Implementation Method 1
a strip casting method is a method in which the molten alloy is cooled with a cooling roll to form an alloy strip
Implementation Method 2
the alloy strip is ground to prepare alloy powder having particle diameters of between several μm and several tens of μm
Implementation Method 3
The alloy powder is then molded and sintered to produce a sintered compact
Data Source
AI summary
An R-T-B based alloy strip including columnar crystals of an R2T14B phase, wherein in a cross-section along the thickness direction, columnar crystals extend out in a radial fashion from the crystal nuclei, the R-T-B based alloy strip satisfying the following inequality (1), where D1 and D2 are, respectively, the average value for the lengths of the columnar crystals on one side and the average value for the lengths on the other side that is opposite the one side, in the direction perpendicular to the thickness direction of the cross-section.0.9/1.1≦D2/D1≦1.1/0.9 (1)