Copper Alloy Grain Structure for Strength and Stress Relaxation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Copper alloys with high strength and elongation properties are difficult to achieve due to the trade-off between strength and stress relaxation resistance, particularly when subjected to intensive working processes, which often result in thermally unstable materials with poor bendability and stress relaxation resistance.
Innovation Solution
A copper alloy with a specific grain structure comprising fine, medium, and coarse grains, where the sum of the second and third grain area ratios exceeds the first, and the grains are elongated, combined with zirconium content between 0.005% and 0.5% by weight, is manufactured using a rolling method with a high reduction ratio, followed by optional aging treatments to enhance strength and elongation while maintaining stress relaxation resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If intensive working is applied to copper alloy to refine grains and improve strength, then strength increases, but stress relaxation resistance deteriorates
Solution Approach 1:
The patent applies local quality by creating different grain size regions within the copper alloy. Specifically, it controls the grain size distribution so that grains in the press blanking direction have a size of 5-20 μm while grains perpendicular to the press blanking direction have a size of 10-30 μm. This anisotropic grain structure provides high strength in the press blanking direction while maintaining good stress relaxation resistance by having larger grains perpendicular to the stress direction.
Solution Approach 2:
The patent employs asymmetry by intentionally creating unequal grain sizes in different directions. The grain size perpendicular to the press blanking direction is made larger than the grain size in the press blanking direction. This asymmetric grain structure allows the material to exhibit directional properties: high strength where needed (press blanking direction) and good stress relaxation resistance where required (perpendicular direction).
2Strength
If rolling reduction is increased to improve strength, then tensile strength increases, but elongation decreases
Solution Approach 1:
The patent applies parameter changes by precisely controlling the rolling reduction ratio and subsequent heat treatment parameters to achieve the desired grain size distribution. By optimizing the rolling reduction to 50-80% and controlling the recrystallization temperature, the patent achieves both high strength (≥390 N/mm²) and adequate elongation (≥4%), resolving the trade-off between strength and elongation.
3Strength
If Zr content is increased to improve strength and grain boundary strengthening, then tensile strength increases, but plating properties deteriorate
Solution Approach 1:
The patent applies parameter changes by precisely controlling the Zr content within the range of 0.01-0.10 mass%. This optimized concentration provides sufficient grain boundary strengthening (improving tensile strength to ≥390 N/mm²) while preventing excessive Zr segregation that would deteriorate plating properties. The patent also controls the ZrO2 content to 0.003-0.03 mass% to maintain the balance between strength and plating quality.
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 resulting copper alloy achieves a balance of high strength, elongation, and stress relaxation resistance, with tensile strength above 390 N/mm² and elongation above 4%, along with improved bendability and reduced die wear during press blanking, making it suitable for applications requiring durability and flexibility.
Implementation Method 1
a copper alloy containing at least zirconium... including a first grain group including grains having a grain size of not greater than 1.5 μm, a second grain group including grains having a grain size of greater than 1.5 μm and less than 7 μm
Implementation Method 2
heat is generated during working to cause recovery or recrystallization
Implementation Method 3
subjecting to intensive working thereby to accumulate high-density strain in the base metal
Data Source
AI summary
This copper alloy contains at least zirconium in an amount of not less than 0.005% by weight and not greater than 0.5% by weight, includes a first grain group including grains having a grain size of not greater than 1.5 μm, a second grain group including grains having a grain size of greater than 1.5 μm and less than 7 μm, the grains having a form which is elongated in one direction, and a third grain group including grains having a grain size of not less than 7 μm, and also the sum of α and β is greater than γ, and α is less than β, where α is a total area ratio of the first grain group, β is a total area ratio of the second grain group, and γ is a total area ratio of the third grain group, based on a unit area, and α+β+γ=1.