Nd-Fe-B Magnet Corrosion Resistance via Two-Alloy Segmentation

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Solution Overview

Problem

Nd—Fe—B permanent magnets exhibit poor corrosion resistance due to their complex microstructure and high reactivity, leading to irreversible loss in coercivity and disintegration, with existing solutions either impairing magnetic properties or being environmentally unfriendly and costly.

Innovation Solution

A sintered Nd—Fe—B permanent magnet with redesigned intergranular-phase alloy composition, characterized by a lower melting point and electrostatic potential equal to or higher than the master-phase alloy, is produced using a two-alloy method, where the intergranular-phase alloy is mixed with master-phase alloy powders to enhance corrosion resistance and magnetic performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If alloying elements are added to improve corrosion resistance, then corrosion resistance is improved, but magnetic properties are impaired

Engineering Contradiction:

Improvecorrosion resistanceVSAvoidmagnetic properties

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The patent divides the alloy into two distinct phases: a master-phase alloy (Nd2Fe14B) that provides magnetic properties and an intergranular-phase alloy that provides corrosion resistance. This segmentation allows each phase to be optimized independently, resolving the contradiction between magnetic performance and corrosion resistance.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent applies different material compositions to different regions of the magnet structure. The master-phase alloy forms the matrix with high magnetic properties, while the intergranular-phase alloy forms the grain boundary regions with high corrosion resistance. This local differentiation allows each region to perform its specific function optimally.

Inventive Principle:

Principle #3Local quality

2Reliability

If protective coatings are applied to improve corrosion resistance, then corrosion resistance is improved, but manufacturing complexity and cost increase

Engineering Contradiction:

Improvecorrosion resistanceVSAvoidmanufacturing complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent creates a magnet that is inherently corrosion-resistant through its internal two-phase structure, eliminating the need for external protective coatings. The intergranular-phase alloy self-provides corrosion protection to the master-phase alloy, simplifying manufacturing and reducing costs.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The patent uses a composite material structure where the intergranular-phase alloy and master-phase alloy are combined at the microstructural level. This intrinsic composite design provides both magnetic and corrosion-resistant properties without requiring additional coating layers or complex manufacturing processes.

Inventive Principle:

Principle #40Composite materials

3Strength

If Nd-rich grain boundary phase is present to form microstructure, then magnetic properties are achieved, but corrosion resistance deteriorates

Engineering Contradiction:

Improvemagnetic propertiesVSAvoidcorrosion resistance

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The patent changes the composition parameters of the grain boundary phase from traditional Nd-rich to an intergranular-phase alloy with specific composition (containing protective elements). This parameter change transforms the grain boundary phase from a corrosion pathway into a protective barrier, resolving the contradiction between magnetic structure and corrosion resistance.

Inventive Principle:

Principle #35Parameter changes

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 significantly reduces mass loss and improves corrosion resistance while maintaining high magnetic properties, with a slight increase in density and refined microstructures that inhibit corrosion propagation.

Implementation Method 1

the electrostatic potential of intergranular-phase alloy is equal to or slightly higher than that of the master-phase alloy

Methodology Applied

Scientific EffectElectrochemical potential difference:

Implementation Method 2

the chemically active netlike Nd-rich grain boundary phase plays an important role in the corrosion process, during which it serves as an effective pathways of intergranular corrosion propagation

Methodology Applied

Scientific EffectIntergranular corrosion:

Implementation Method 3

produced using a two-alloy method, where the intergranular-phase alloy is mixed with master-phase alloy powders

Methodology Applied

Scientific EffectPowder metallurgy:

Implementation Method 4

refined microstructures that inhibit corrosion propagation

Methodology Applied

Scientific EffectMicrostructure refinement:

Data Source

PatentUS9818515B2Modified Nd—Fe—B permanent magnet with high corrosion resistance

Publication Date: 2017.11.14 ZHEJIANG INNUOVO MAGNETICS IND

AI summary

A type of sintered Nd—Fe—B permanent magnet with high corrosion resistance is produced by dual alloy method. The method comprises the following steps: preparing the powders of master phase alloy and intergranular phase alloy respectively, mixing the powders, compacting the powders in magnetic field, sintering the compacted body at 1050˜1125° C., and annealing at 920-1020° C. and 500-650° C. successively.