R-T-B Alloy Microstructure Control via Strip Casting
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Solution Overview
Problem
R-T-B type rare earth permanent magnets face challenges in achieving uniform dispersion of the R-rich phase and eliminating α-Fe, which affects magnetic characteristics and grinding efficiency, requiring advanced control of alloy texture and cooling rates during the strip casting method.
Innovation Solution
The R-T-B type alloy is produced with a specific microstructure containing a fine R2T17 phase and R-rich phase, achieved by controlling the cooling rate and temperature during the strip casting method, resulting in an alloy flake with enhanced magnetic characteristics and coercive force.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the cooling rate during strip casting is increased to suppress α-Fe precipitation and improve magnetic characteristics, then the magnetic properties are improved, but the manufacturing complexity and control difficulty increase
Solution Approach 1:
The patent applies parameter changes by optimizing the cooling rate within a specific range (500-3000°C/sec) and controlling the alloy composition (R: 20-35 mass%, T: 60-75 mass%, B: 1-5 mass%) to achieve the desired microstructure. This resolves the contradiction by finding the optimal parameter window that suppresses α-Fe while maintaining manufacturing feasibility
Solution Approach 2:
The patent uses preliminary action by performing homogenization heat treatment before strip casting to ensure uniform composition distribution, and by pre-controlling the alloy composition to prevent α-Fe formation during rapid cooling. This preparatory work reduces the complexity of controlling cooling rates during the actual casting process
2Stability of the object's composition
If the strip casting method is used to produce fine alloy flakes with controlled microstructure, then the uniform dispersion of R-rich phase is improved, but the manufacturing precision requirements increase
Solution Approach 1:
The patent controls the microstructure by adjusting the cooling rate parameter and alloy composition, achieving a specific phase distribution (R2T14B main phase with dispersed R-rich phase). This parameter optimization ensures uniform dispersion while maintaining achievable manufacturing precision
Solution Approach 2:
The patent utilizes phase transitions during rapid cooling, where the alloy transforms from molten state to solidified flake with specific microstructure. The controlled phase transition during cooling creates the desired uniform dispersion of R-rich phase without requiring excessive manufacturing precision
3Reliability
If homogenization treatment is performed to eliminate α-Fe, then the magnetic characteristics are improved, but the processing time and energy consumption increase
Solution Approach 1:
The patent performs homogenization heat treatment as a preliminary step before strip casting to eliminate α-Fe and ensure uniform composition. By completing this treatment beforehand, the subsequent rapid cooling process can proceed quickly without requiring additional long treatment times, thus reducing overall processing time
Solution Approach 2:
The patent optimizes the homogenization treatment parameters (temperature, time, atmosphere) to achieve effective α-Fe elimination in the minimum necessary time. By precisely controlling these parameters, the treatment is both effective and time-efficient
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 leads to improved magnetic characteristics and coercive force of the R-T-B type rare earth permanent magnets by ensuring uniform dispersion of the R-rich phase and suppressing α-Fe precipitation, enhancing the sinterability and grinding stability of the alloy.
Implementation Method 1
a casting roll, with an inside being water-cooled
Implementation Method 2
with an inside being water-cooled
Data Source
AI summary
An R-T-B type alloy (wherein R is at least one member selected from rare earth elements, T is a transition metal including Fe, and B includes 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%.