Al–Zn–Cu–Mg Alloy Composition for Thick Rolled Strength and EAC Resistance
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Solution Overview
Problem
Existing Al-Zn-Cu-Mg alloys used in aerospace applications face challenges in achieving a balance between high strength, fracture toughness, and resistance to environmentally assisted cracking (EAC) under conditions of high stress and humid environments, particularly in thick rolled products.
Innovation Solution
A specific composition range for Al-Zn-Cu-Mg alloys with Zn 6.9-7.5%, Mg 1.8-2.2%, Cu 1.8-2.2%, and controlled Cu+Mg ratio of 3.8-4.2%, combined with a manufacturing process involving ingot casting, homogenization, hot rolling, solution heat treatment, quenching, stretching, and artificial aging at 155°C for 24-70 hours, to produce rolled products with improved mechanical strength and EAC resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If higher zinc and copper content is used to increase strength, then mechanical strength is improved, but resistance to environmentally assisted cracking deteriorates
Solution Approach 1:
The invention optimizes the chemical composition parameters by precisely controlling zinc content at 6.9-7.5% and copper content at 1.8-2.2%, along with magnesium at 1.8-2.2%. This specific parameter range achieves the desired balance between mechanical strength and EAC resistance, resolving the contradiction by finding the optimal compositional window where both properties are satisfied simultaneously.
Solution Approach 2:
The invention creates a composite alloy system Al-Zn-Cu-Mg where multiple elements work synergistically. The specific combination of zinc (6.9-7.5%), copper (1.8-2.2%), and magnesium (1.8-2.2%) forms a composite material structure that provides both high strength and excellent EAC resistance, overcoming the limitations of individual element additions.
2Strength
If longer artificial aging time is used to increase strength, then mechanical strength is improved, but productivity deteriorates
Solution Approach 1:
The invention optimizes the aging parameter by specifying a time range of 24-70 hours at 155°C, with a preferred range of 28-40 hours. This parameter optimization achieves the necessary mechanical strength while minimizing production time, resolving the contradiction between strength development and production efficiency.
Solution Approach 2:
The invention establishes a standardized aging process protocol that can be replicated and optimized. By defining specific aging conditions (155°C for 24-70 hours), the process creates a reliable template that ensures consistent strength properties while maintaining efficient production cycles across different batches.
3Device complexity
If thicker rolled products are produced to reduce the number of components, then structural complexity is reduced, but manufacturing precision deteriorates
Solution Approach 1:
The invention maintains manufacturing precision in thick products (≥50 mm) by optimizing compositional parameters (Zn: 6.9-7.5%, Cu: 1.8-2.2%, Mg: 1.8-2.2%) and process parameters (solution heat treatment at 460-510°C, quenching, and aging at 155°C for 24-70 hours). These controlled parameters ensure uniform microstructure and properties throughout the thick section, overcoming the difficulty of maintaining precision in large-scale products.
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 results in rolled products with enhanced mechanical strength, fracture toughness, and resistance to EAC under high stress and humid conditions, exhibiting a minimum life without failure of at least 40 days, with tensile yield strength of 467-0.27*t MPa and K1C toughness of 26-0.01*t MPa√m, suitable for structural members in aircraft construction.
Implementation Method 1
solution heat treating and quenching the product
Implementation Method 2
solution heat treating and quenching the product
Implementation Method 3
artificial aging with the equivalent aging time t(eq) at 155° C. is comprised between 24 and 70 hours
Implementation Method 4
homogenizing the ingot
Data Source
AI summary
The invention relates to a rolled product made of aluminum alloy with a thickness of at least 50 mm comprising (in weight %): Zn 6.9-7.5; Mg 1.8-2.2; Cu 1.8-2.2, where the sum Cu+Mg is between 3.8 and 4.2; Zr 0.04-0.14; Mn 0-0.1; Ti 0-0.15; V 0-0.1; Fe ≤0.15; If ≤0.15; impurities ≤0.05 each and ≤0.15 total, balance aluminum. The invention also relates to the method of manufacturing such a product. The products according to the invention are particularly advantageous because they have a very favorable compromise between static mechanical strength, toughness and environmental-assisted cracking performance under conditions of high stress and humid environment.