Copper Alloy Fastener Element With Low β Phase for Season Cracking Resistance
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Solution Overview
Problem
Copper-zinc alloys used in fasteners face issues with season cracking due to residual stresses and corrosion, particularly when zinc content exceeds 10% by mass, leading to reduced strength and increased material costs, while increasing the β phase ratio improves strength but lowers cold workability and mold life.
Innovation Solution
A copper-zinc alloy with a dendrite structure and a β phase ratio of 10% or less, produced through specific annealing and casting processes, maintains improved season cracking resistance without adversely affecting cold workability and mold life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If zinc content is increased to improve strength and cold workability, then strength and uniform deformation amount are improved, but corrosion resistance deteriorates and season cracking occurs
Solution Approach 1:
The invention optimizes the zinc content parameter within a specific range (10-38 mass%) to balance strength and corrosion resistance. By precisely controlling the zinc content parameter rather than simply increasing it, the alloy achieves sufficient strength while maintaining corrosion resistance and preventing season cracking.
Solution Approach 2:
The invention creates a composite microstructure consisting of α phase and β phase regions with different characteristics. The α phase provides ductility and corrosion resistance, while the β phase contributes strength. This composite phase structure allows the alloy to simultaneously achieve high strength and good corrosion resistance despite containing zinc.
2Strength
If zinc content is increased above 10% by mass to improve strength, then strength increases, but season cracking resistance decreases
Solution Approach 1:
The invention changes the zinc content parameter from the conventional limit of <10 mass% to a broader range of 10-38 mass%, demonstrating that season cracking resistance can be maintained even with higher zinc content through proper microstructure control. The key is optimizing the phase composition rather than simply limiting zinc content.
Solution Approach 2:
The invention uses a composite phase structure where α phase and β phase coexist in specific proportions. This composite structure prevents season cracking by creating a microstructure that can accommodate residual stresses without cracking, even when zinc content exceeds the conventional 10% threshold.
3Strength
If β phase ratio is increased to improve strength, then strength increases, but cold workability decreases and mold life shortens
Solution Approach 1:
The invention optimizes the β phase ratio parameter within a specific range rather than maximizing it. By controlling the β phase ratio to an optimal level, the alloy achieves sufficient strength while maintaining adequate cold workability and extending mold life, resolving the trade-off between strength and manufacturability.
Solution Approach 2:
The invention creates local variations in phase composition and crystal grain structure throughout the material. By controlling the distribution and morphology of α and β phases at the microstructural level, the alloy achieves strength where needed while maintaining cold workability in regions subjected to deformation during manufacturing.
4Reliability
If third elements such as tin are added to prevent season cracking, then season cracking resistance improves, but material cost increases and cold workability deteriorates
Solution Approach 1:
The invention extracts the season cracking prevention function from third element additives (such as tin) and achieves it through optimized zinc content control and phase structure design within the copper-zinc binary system. This eliminates the need for expensive third elements while maintaining cold workability.
Solution Approach 2:
The invention replaces expensive third elements (tin and other season cracking prevention additives) with a cost-effective zinc content optimization strategy. By using zinc, which is cheaper than tin, within an optimized range and controlling the phase structure, the invention achieves season cracking resistance at lower material cost without sacrificing cold workability.
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 enhances season cracking resistance and mold life by maintaining a small β phase ratio, reducing material costs, and improving industrial productivity of copper alloy fasteners.
Implementation Method 1
a two-phase structure of an α phase and a β phase, wherein a ratio of the β phase in the copper-zinc alloy is controlled to be greater than 10% and less than 40%
Implementation Method 2
crystal grains of the α phase and the β phase are crushed into a flat shape by cold working so that the crystal grains are arranged in the form of layer
Data Source
AI summary
Provided is a copper alloy fastener element which improves season cracking resistance by a means different from that of increasing a ratio of a β phase. The copper alloy fastener element includes a copper-zinc alloy as a base material, the base material having: an apparent zinc content of from 34 to 38%; a dendrite structure; and a β phase at a ratio of 10% or less.