Zinc-Rich Copper Alloy Fastener Season Cracking Resistance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Copper alloy fasteners with high zinc content face issues with season cracking resistance and increased manufacturing costs due to the need for surface treatments and strict composition control of mixed phases, which compromise cold workability and economic efficiency.
Innovation Solution
A metallic fastener member with a copper alloy surface treated to form a concentrated layer of manganese near the surface, combined with a rust prevention treatment using nitrogen-containing compounds, enhances season cracking resistance without requiring shot blasting or strict heat treatment conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If zinc content in copper alloy is increased to improve strength and hardness, then alloy strength and uniform deformation are improved, but season cracking resistance is rapidly deteriorated
Solution Approach 1:
The patent applies local quality by creating a surface layer with different composition (enriched in Cu and Ni, depleted in Zn) compared to the bulk alloy. This surface layer with 5-20 μm thickness has improved season cracking resistance while the bulk alloy maintains high Zn content (35-40 mass%) for strength. The selective removal of Zn from the surface through controlled corrosion or pickling creates this compositional gradient.
Solution Approach 2:
The patent creates a composite structure with two distinct zones: a surface layer enriched in Cu and Ni with low Zn content that provides corrosion and season cracking resistance, and a bulk alloy with high Zn content (35-40 mass%) that provides strength and hardness. This composite architecture allows simultaneous optimization of contradictory properties.
2Reliability
If zinc content is decreased to less than 10% to improve season cracking resistance, then season cracking resistance is improved, but material cost increases and strength becomes insufficient
Solution Approach 1:
Instead of uniformly reducing Zn content throughout the alloy (which would weaken it), the patent applies local quality by creating a surface layer with low Zn content (5-20 μm thick) that provides season cracking resistance, while the bulk alloy maintains high Zn content (35-40 mass%) for strength. This localized approach solves the contradiction spatially.
Solution Approach 2:
The patent segments the alloy into two functional zones: a surface layer (5-20 μm thick) with modified composition for environmental resistance, and a bulk alloy with standard high-Zn composition for mechanical strength. This segmentation allows each zone to be optimized for its specific function without compromise.
3Reliability
If surface treatments such as shot blasting are applied to improve season cracking resistance, then season cracking resistance is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The patent changes the chemical composition parameter of the surface layer by controlling the alloy composition (Cu: 55-65 mass%, Zn: 35-40 mass%, Ni: 0.1-1 mass%) and applying controlled corrosion or pickling treatment. This chemical parameter change creates a protective surface layer without requiring mechanical surface treatments like shot blasting, simplifying the manufacturing process.
Solution Approach 2:
The patent extracts Zn selectively from the surface layer through controlled corrosion or pickling treatment, creating a Zn-depleted surface layer (5-20 μm thick) that is enriched in Cu and Ni. This extraction process creates the protective surface layer in situ without requiring additional surface treatment equipment or processes.
4Reliability
If strict control of β phase ratio (greater than 10% and less than 40%) is implemented to improve season cracking resistance, then season cracking resistance is improved, but manufacturing precision requirements increase and production constraints are added
Solution Approach 1:
The patent changes the approach from controlling phase ratios (which requires precise heat treatment and composition control) to controlling the surface layer composition and thickness. By specifying Cu content (55-65 mass%), Zn content (35-40 mass%), Ni content (0.1-1 mass%), and surface layer thickness (5-20 μm), the patent simplifies manufacturing control while achieving improved season cracking resistance.
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
This approach improves season cracking resistance and manufacturability by reducing processing steps and costs, maintaining adequate strength and cold workability, while achieving a 70% or more retention of pull-out strength after ammonia exposure.
Implementation Method 1
a maximum value of an atomic concentration of Mn is detected at a depth of 100 nm or less from the surface
Implementation Method 2
a rust prevention treatment has been applied
Data Source
AI summary
An improved season cracking resistance of a metallic fastener member is provided and includes a copper alloy containing zinc as a base material. The metallic fastener member includes, as a base material, a copper alloy containing zinc, and the metallic fastener member has a surface to which a rust prevention treatment has been applied and has such a property that, when analyzed by a scanning X-ray photoelectron spectroscopy apparatus, a maximum value of an atomic concentration of Mn is detected at a depth of 100 nm or less from the surface.