Cu-Zn-Mn Alloy Phase Control for Season Cracking
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Solution Overview
Problem
Cu—Zn-based alloys used for fastening materials face challenges with increased zinc content, leading to deterioration in corrosion resistance and season cracking due to residual work strain, and existing solutions require complex processing and high manufacturing costs.
Innovation Solution
A copper alloy with a mixture of α-phase and β-phase structure, specifically formulated as CuBal.ZnaMnb, where 34≤a≤40.5 and 0.1≤b≤6, with controlled β-phase percentage and mean crystal grain size, optimized for improved cold-workability and season cracking resistance, and incorporating manganese to enhance properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If zinc content is increased to reduce material cost, then manufacturing cost decreases, but corrosion resistance deteriorates and season cracking occurs
Solution Approach 1:
The invention changes the compositional parameters by precisely controlling zinc content (34-40.5%) and manganese content (0.1-6%) within specific ranges, and controlling the β-phase percentage (0.1-22%) to achieve both cost reduction and maintained reliability
Solution Approach 2:
The invention creates a composite microstructure consisting of α-phase and β-phase in controlled proportions, where the dual-phase structure provides both mechanical properties and resistance to season cracking while allowing higher zinc content for cost reduction
2Ease of manufacture
If zinc content is increased to reduce material cost, then manufacturing cost decreases, but season cracking resistance deteriorates
Solution Approach 1:
The invention introduces manganese content (0.1-6%) as an additional parameter to control season cracking resistance, and establishes specific relationships between zinc and manganese content through equations (1) and (2) to prevent season cracking while maintaining high zinc content for cost reduction
Solution Approach 2:
The controlled dual-phase structure (α-phase and β-phase) with specific phase percentages provides a microstructural basis for resisting season cracking while allowing high zinc content, creating a composite material system that addresses both cost and reliability concerns
3Ease of manufacture
If alloy structure is made into single phase α for cold-workability, then cold workability improves, but zinc concentration increase becomes undesirable due to β-phase formation
Solution Approach 1:
The invention optimizes the compositional parameters (zinc 34-40.5%, manganese 0.1-6%) to control the phase transformation behavior, allowing the alloy to maintain a stable dual-phase structure at room temperature while preserving excellent cold-workability during processing
Solution Approach 2:
The invention deliberately creates and controls a composite microstructure of α-phase and β-phase in specific proportions (β-phase: 0.1-22%), where this controlled composite structure provides both cold-workability and compositional stability, overcoming the limitation of single-phase structures
4Reliability
If complex processing such as shot-blasting is applied to enhance season cracking resistance, then season cracking resistance improves, but manufacturing process complexity increases
Solution Approach 1:
The invention enables the alloy to achieve season cracking resistance through its inherent compositional design (controlled zinc and manganese content) and microstructure (dual-phase structure), eliminating the need for external surface treatments like shot-blasting and allowing the material to resist season cracking through its own properties
Solution Approach 2:
The invention achieves season cracking resistance by optimizing compositional parameters (zinc 34-40.5%, manganese 0.1-6%) and microstructural parameters (β-phase 0.1-22%), replacing complex surface treatment processes with precise compositional control during manufacturing
Data Source
AI summary
A copper alloy for fastening wherein the alloy has a structure of a mixture of α-phase and a β-phase; and wherein the alloy has a composition represented by the general formula: Cubal.ZnaMnb, where bal., a, and b are expressed in % by mass, bal. represents the balance, 34≤a≤40.5, 0.1≤b≤6, and inevitable impurities may be contained; and the composition satisfying the equation (1): b≥(−8a+300)/7, where 34≤a<37.5 and equation (2): b≤(−5.5a+225.25)/5, where 35.5≤a≤40.5.