Copper Alloy Wire Surface Hardening for Fatigue Resistance
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Solution Overview
Problem
Conventional copper alloy wires with small diameters face challenges in achieving enhanced resistance to bending fatigue and strength while maintaining electrical conductivity and elongation, leading to issues like wire breakage during working and high costs due to high Ag content, and difficulties in applying surface working techniques effectively.
Innovation Solution
A copper alloy wire with an alloy composition of 0.5 to 4% Ag and/or 0.05 to 0.3% of elements like Sn, Mg, Zn, In, Ni, Co, Zr, and Cr, subjected to semi-softening treatment followed by cold-working to achieve a nanoindentation hardness of 1.45 GPa or more at the surface and less than 1.45 GPa at the center, ensuring sufficient elongation and resistance to bending fatigue.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high-concentration Cu-Ag alloy containing 2 to 15 mass% of Ag is used to enhance tensile strength, then physical strength is improved, but electrical conductivity is lowered and cost increases
Solution Approach 1:
The patent applies local quality by creating a dual-zone hardness structure where the wire surface section has high hardness (1.45 GPa or more) for fatigue resistance while the wire center maintains lower hardness for ductility. This is achieved through controlled cold-working that affects only the surface layer, allowing the core to retain better mechanical properties and electrical conductivity characteristics.
Solution Approach 2:
The patent changes the hardness parameter distribution along the wire cross-section by controlling the cold-working degree. The surface section is cold-worked to achieve hardness of 1.45 GPa or more, while the center maintains hardness below 1.45 GPa. This parameter differentiation resolves the contradiction between strength and conductivity by optimizing each zone for its specific function.
2Strength
If Ag content is increased to further increase physical strength, then tensile strength is enhanced, but electrical conductivity is lowered and cost increases noticeably
Solution Approach 1:
The patent uses local quality by differentiating the hardness between surface and center zones through controlled cold-working. The surface section (extending to maximum 20% of wire diameter from the outermost surface) achieves high hardness for fatigue resistance, while the center maintains lower hardness, preserving electrical conductivity and reducing the need for high Ag content.
Solution Approach 2:
The patent creates a composite structure within the homogeneous copper alloy material by inducing a hardness gradient through cold-working. The surface layer acts as a hardened protective zone while the core remains softer, effectively creating a functionally graded material that balances strength, conductivity, and cost.
3Reliability
If surface working is applied to soft copper wire with diameter φ0.1 mm or less to enhance resistance to bending fatigue, then fatigue resistance is improved, but wire breakage occurs due to low strength during working
Solution Approach 1:
The patent applies preliminary action by performing controlled cold-working at an intermediate stage during wire drawing, before the wire reaches its final ultra-fine diameter. This preliminary hardening of the surface section provides the necessary strength to prevent breakage in subsequent processing steps while establishing the hardness gradient needed for fatigue resistance.
Solution Approach 2:
The patent changes the hardness parameter during the manufacturing process by applying cold-working at specific stages. The surface section hardness is increased to 1.45 GPa or more through controlled cold-working, while maintaining center hardness below 1.45 GPa, thereby preventing wire breakage during further processing and ensuring final fatigue resistance.
4Strength
If cold-working is applied to enhance tensile strength, then physical strength is improved, but elongation is lowered
Solution Approach 1:
The patent applies local quality by restricting cold-working effects to the surface section of the wire, extending maximum to 20% of the wire diameter from the outermost surface. This localized hardening improves tensile strength and fatigue resistance at the surface while the softer center maintains ductility and elongation properties.
Solution Approach 2:
The patent changes the hardness parameter distribution by controlling cold-working degree and duration. The surface section achieves hardness of 1.45 GPa or more for strength, while the center maintains hardness below 1.45 GPa to preserve elongation, effectively decoupling the strength-elongation trade-off through spatial parameter differentiation.
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 solution provides copper alloy wires with improved resistance to bending fatigue and elongation, enabling the production of extra-fine magnet wires with enhanced physical strength and electrical conductivity, reducing the risk of wire breakage and production costs.
Implementation Method 1
subjected to semi-softening treatment followed by cold-working
Implementation Method 2
subjected to semi-softening treatment followed by cold-working to achieve a nanoindentation hardness of 1.45 GPa or more at the surface
Data Source
Figure 1
AI summary
{Problem to solve} To provide, at low cost, a copper alloy wire that is excellent in elongation, and resistance to bending fatigue, and that can be suitable for the use in, for example, magnet wires. {Means to solve} A copper alloy wire, having an alloy composition containing 0.5 to 4 mass% of Ag, and at least one selected from the group consisting of Sn, Mg, Zn, In, Ni, Co, Zr, and Cr each at a content of 0.05 to 0.3 mass%, with the balance being Cu and unavoidable impurities, wherein the copper alloy wire has a wire diameter or a wire thickness of 0.1 mm or less, and wherein the nanoindentation hardness in a depth region extending from the outermost surface of the wire toward at least 5% inner side in the wire diameter or the wire thickness is 1.45 GPa or more, the nanoindentation hardness at the center of the wire is less than 1.45 GPa, the tensile strength of the wire is 350 MPa or more, and the elongation of the wire is 7% or more; and a method of producing the copper alloy wire.