R-T-B Sintered Magnet Coercivity via Controlled Cooling
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Solution Overview
Problem
R-T-B based sintered magnets face challenges in achieving high coercivity (HcJ) without rapid cooling, which can lead to thermal stress and variations in magnetic properties due to inconsistent cooling rates during the heat treatment process.
Innovation Solution
A method involving a high-temperature heat treatment step at 730° C. to 1,020° C., followed by slow cooling to 300° C. at a rate of 5° C./min or more, and a low-temperature heat treatment step at 440° C. to 550° C., with specific compositions and cooling rate controls to form the R—Ga—Cu phase while suppressing the R-T-Ga phase, enabling high HcJ without rapid cooling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If rapid cooling is applied during heat treatment to achieve high HcJ, then coercivity is improved, but thermal stress and variations in magnetic properties occur due to inconsistent cooling rates
Solution Approach 1:
The patent applies parameter changes by precisely controlling the cooling rate within the range of 5°C/min to 50°C/min during high-temperature heat treatment (730°C to 1,020°C). This controlled cooling rate parameter transformation allows the formation of the R-Ga-Cu phase while suppressing the R-T-Ga phase, achieving high coercivity without the adverse effects of rapid cooling such as thermal stress and magnetic property variations.
2Strength
If heavy rare earth elements (mainly Dy) are added in large amounts to improve HcJ, then coercivity is improved, but residual magnetic flux density (Br) is reduced
Solution Approach 1:
The patent replaces expensive heavy rare earth elements (Dy) with more abundant and cost-effective elements (Ga and Cu) to achieve the same coercivity enhancement. By forming the R-Ga-Cu phase through controlled cooling, the patent reduces dependency on scarce heavy rare earth elements while maintaining high HcJ performance, effectively substituting expensive materials with cheaper alternatives.
Solution Approach 2:
The patent creates a composite phase structure by forming the R-Ga-Cu phase through controlled cooling of the sintered magnet. This composite approach combines multiple elements (rare earth R, gallium Ga, and copper Cu) in a specific phase configuration that achieves high coercivity without requiring large amounts of heavy rare earth elements, thereby preserving residual magnetic flux density.
3Ease of manufacture
If the cooling rate is not controlled during sintering, then production simplicity is maintained, but the R-T-Ga phase forms excessively and HcJ is limited
Solution Approach 1:
The patent applies parameter changes by implementing a specific cooling rate control (5°C/min to 50°C/min) during the high-temperature heat treatment stage (730°C to 1,020°C). This parameter transformation from uncontrolled to controlled cooling enables the suppression of the R-T-Ga phase and promotion of the R-Ga-Cu phase, achieving high coercivity while maintaining production feasibility through a clearly defined process parameter.
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 allows for the production of R-T-B based sintered magnets with high HcJ and reduced heavy rare earth element usage, maintaining magnetic properties consistency across larger magnet sizes and varying cooling conditions.
Implementation Method 1
a high-temperature heat treatment step of heating the R-T-B based sintered magnet material to a heating temperature of 730° C. or higher and 1,020° C. or lower and then cooling the R-T-B based sintered magnet material to 300° C. at a cooling rate of 5° C./min or more
Implementation Method 2
heating the R-T-B based sintered magnet material to a heating temperature of 730° C. or higher and 1,020° C. or lower and then cooling the R-T-B based sintered magnet material to 300° C. at a cooling rate of 5° C./min or more
Data Source
AI summary
A method for manufacturing an R-T-B based sintered magnet includes: 1) a step of preparing an R-T-B based sintered magnet material by sintering a molded body, the sintered magnet material having a particular composition and satisfying inequality expressions (1) and (2); 2) a high-temperature heat treatment step of heating the sintered magnet material to a heating temperature of 730° C. to 1,020° C. and then cooling the sintered magnet material to 300° C. at a cooling rate of 5° C./min or more; and 3) a low-temperature heat treatment step of heating the sintered magnet material after the high-temperature heat treatment step to 440° C. to 550° C.:[T]−72.3[B]>0 (1)([T]−72.3[B])/55.85<13[Ga]/69.72 (2)where [T] is a T content in percent by mass, [B] is a B content in percent by mass, and [Ga] is a Ga content in percent by mass.