R-T-B Alloy Flake Production via Rapid Strip Casting
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Solution Overview
Problem
Current methods for producing R-T-B type alloy flakes do not adequately enhance magnetic characteristics, particularly coercive force, due to issues with α-Fe production and R-rich phase dispersion, which affect the quality and efficiency of sintered magnets.
Innovation Solution
A strip casting method is employed to produce R-T-B type alloy flakes with controlled cooling rates and molten alloy supply rates, resulting in a fine R 2 T 17 phase distribution, which enhances magnetic characteristics by stabilizing coercive force and improving texture homogeneity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a homogenization treatment at high temperature is applied for a long time to eliminate α-Fe, then α-Fe can be removed from the raw material alloy, but the production time and energy consumption increase significantly
Solution Approach 1:
The invention changes the cooling rate parameter during casting from conventional slow cooling to rapid cooling (10^2 to 10^4 K/s), which fundamentally alters the solidification path and prevents α-Fe formation through kinetic control rather than thermodynamic equilibrium
Solution Approach 2:
The invention utilizes phase transition control by rapidly cooling the molten alloy to suppress the formation of α-Fe phase during solidification, directing the phase transformation toward desired R2T14B and R-rich phases instead
2Reliability
If the R-rich phase is not uniformly dispersed in the shaped magnet, then local failure of sintering or reduction of magnetism occurs, but achieving uniform dispersion requires precise control of raw material alloy texture
Solution Approach 1:
The invention changes the cooling rate parameter during casting to create a fine cellular dendritic structure with uniform R-rich phase distribution, achieving reliable sintering outcomes without requiring complex post-casting texture control procedures
Solution Approach 2:
The invention performs preliminary action by establishing the desired R-rich phase dispersion pattern during the casting process itself through controlled rapid cooling, rather than requiring subsequent complex processing steps to achieve uniform distribution
3Manufacturing precision
If α-Fe remains in the magnet after sintering, then the magnetic characteristics of the magnet are reduced, but eliminating α-Fe requires solid phase diffusion for a long time
Solution Approach 1:
The invention prevents α-Fe phase transition during solidification by rapid cooling, eliminating the need for subsequent long-duration solid phase diffusion processes to remove unwanted α-Fe inclusions
Solution Approach 2:
The invention skips the intermediate step of allowing α-Fe to form and then requiring lengthy diffusion treatment by directly rapidly cooling through the temperature range where α-Fe would form, rushing through the problematic phase formation zone
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 method produces alloy flakes with a high coercive force and excellent magnetic characteristics by controlling the R 2 T 17 phase distribution, leading to improved sinterability and reduced α-Fe precipitation, thus enhancing the magnetic properties of sintered magnets.
Implementation Method 1
a flake of 0.1 to 1 mm is produced through solidification upon a casting roll
Implementation Method 2
a molten alloy is cast on a copper roll of which inside is water-cooled, and a flake of 0.1 to 1 mm is produced through solidification
Implementation Method 3
The R-rich phase expands by reacting with hydrogen in a hydrogen atmosphere and becomes a brittle hydride
Data Source
Figure 1~2
Figure 3
AI summary
The present invention provides an R-T-B type alloy as a raw material of a rare earth-based permanent magnet having excellent magnetic characteristics. The present invention provides an R-T-B type alloy (wherein R is at least one member selected from rare earth elements including Y, T is a transition metal essentially comprising Fe, and B is boron) which is a raw material for use in a rare earth-based permanent magnet, wherein the volume percentage of the region containing an R2T17 phase having an average grain diameter of 3 µm or less in the short axis direction is from 0.5 to 10%.