Hot-Pressed NdFeB Magnet Processing for High Coercivity
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Solution Overview
Problem
Existing methods for preparing rare-earth permanent magnets by hot press molding face challenges in achieving uniform coating of thin films on particle surfaces, leading to non-uniform distribution of Dy or Tb, which reduces material performance and makes it inferior to sintered magnets.
Innovation Solution
A method involving smelting an RFeB alloy with specific rare-earth and metal compositions, followed by HD treatment, jet pulverization, magnetic field molding, preheating, hot pressing, and aging to achieve high coercive force without excessive heavy rare-earth elements, where RTM alloys permeate the grain boundaries and surface layers to enhance magnetic properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a thin film coating method is used to achieve uniform distribution of Dy or Tb on particle surfaces, then the manufacturing precision and material performance improve, but the ease of manufacture deteriorates due to the difficulty of implementing such coating processes
Solution Approach 1:
The patent changes the physical-chemical parameters of the coating process by using plasma treatment to activate particle surfaces, followed by dip-coating in molten rare-earth alloy at controlled temperatures (450-650°C). This transforms an otherwise impossible thin-film coating task into a feasible process that achieves uniform 1-10 nm film thickness on 1-5 μm particles.
Solution Approach 2:
The patent introduces plasma as an intermediary to prepare the particle surface before coating. The plasma treatment creates a reactive surface that readily accepts the rare-earth alloy coating, enabling uniform thin-film deposition without requiring complex specialized coating equipment.
2Strength
If excessive rich phase is added to improve coercive force, then the magnetic performance improves, but the residual magnetism decreases and overall performance deteriorates
Solution Approach 1:
The patent applies local quality by concentrating the rare-earth elements (Dy, Tb) specifically at the grain boundaries and particle surfaces through controlled coating, rather than distributing them uniformly throughout the bulk material. This localized enrichment provides the necessary coercive force while maintaining the bulk material's high residual magnetism properties.
Solution Approach 2:
The patent precisely controls the coating parameters including molten alloy temperature (450-650°C), coating duration (5-30 minutes), and rare-earth content (0.1-5 wt%) to achieve the optimal balance between coercive force enhancement and residual magnetism preservation, avoiding the performance degradation caused by excessive rich phase.
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 significantly improves coercive force and reduces residual magnetism, achieving coercive forces above 1350 KA/m without adding heavy rare-earth elements, while optimizing material performance and reducing costs by selective use of rare-earth elements like Dy, Tb, and Ho.
Implementation Method 1
performing HD treatment on the master alloy, and permeating an RTM alloy during this process
Implementation Method 2
performing jet pulverization on the product obtained in the step 2)
Implementation Method 3
molding under a magnetic field at room temperature
Implementation Method 4
preheating the green body in vacuum... The absorbed gas was discharged, and various organic additives and residual hydrogen are volatilized
Implementation Method 5
a pressure of 25 to 120 MPa is applied for hot pressing. The density reaches 99.8% to 99.9% of the theoretical density
Implementation Method 6
during preheating and aging treatment, the rare-earth element will partially diffuse into the surface layer of the main phase
Data Source
AI summary
The present invention relates to a method for preparing a neodymium-iron-boron rare-earth permanent magnetic material, in particular to a hot press molding-based method for preparing a rare-earth permanent magnet. The problem that the residual magnetism and coercive force of a rare-earth permanent magnet prepared in the prior art cannot be both high is solved. An RTM alloy infiltrates same during an HD treatment. RTM sticks to the surface of coarse powder and infiltrates into the interior of the coarse powder along a grain boundary. The temperature of hot press sintering is relatively low, and grains barely grow. In the absence of Dy and Tb, a higher coercive force is obtained. If an alloy containing Dy and Tb is used for infiltration, these atoms diffuse into the surface layer of a main phase during preheating and heat treatment, achieving grain boundary hardening. Under the premise of a very small reduction in the residual magnetism, the coercive force is greatly improved.