7050 Large Diameter Aluminum Alloy Forged Ring

The 7050 large diameter aluminum alloy forged ring is an ultra-high-strength, heat-treatable aluminum-zinc-magnesium-copper alloy (Al-Zn-Mg-Cu series), specifically designed for structural components in aerospace and defense applications that demand extremely high strength, excellent fracture toughness, and good resistance to stress corrosion cracking (SCC) and exfoliation corrosion. Compared to 7075 alloy, also in the 7xxx series, 7050 achieves significantly improved fracture toughness and SCC resistance in thick sections, while maintaining excellent strength, through optimized alloy composition (lower copper content and higher zinc/magnesium ratio) and stringent production process control. Large diameter forged rings leverage the advantages of the forging process, resulting in a dense internal structure, refined grains, and an optimized grain flow aligned along the ring’s circumference, ensuring outstanding reliability and long service life under the most severe operating conditions.

Primary Alloying Elements:

Zinc (Zn): 5.9-6.7% (primary strengthening element)

Magnesium (Mg): 2.0-2.6% (synergistic strengthening with zinc, enhances age-hardening response)

Copper (Cu): 2.0-2.6% (increases strength, but excessive amounts can reduce SCC resistance)

Zirconium (Zr): 0.08-0.15% (forms Al₃Zr dispersoids, refines grains, inhibits recrystallization)

Base Material:

Aluminum (Al): Balance

Controlled Impurities:

Iron (Fe): 0.15% max

Silicon (Si): 0.12% max

Manganese (Mn): 0.10% max

Titanium (Ti): 0.06% max

Other elements: 0.05% max each, 0.15% max total

Premium Forging Process (for Large Diameter Rings): Producing 7050 large diameter aluminum alloy forged rings represents the pinnacle of aerospace-grade forging technology, requiring precise control over melting, forging, and heat treatment processes to ensure the material achieves ultimate comprehensive performance:

Melt and Ingot Preparation:

High-ppurity primary aluminum and high-purity alloying elements are used.

Advanced melting and casting technologies such as vacuum melting, inert gas protection, SNIF/filtration, and electromagnetic stirring are employed to ensure extremely low hydrogen content and non-metallic inclusions in the melt, meeting aerospace-grade cleanliness.

Large Direct-Chill (DC) casting or continuous casting systems are used to produce large diameter ingots with uniform, segregation-free microstructures. The addition of Zirconium (Zr) forms Al₃Zr dispersoids during solidification, effectively refining as-cast grains and inhibiting recrystallization, which is crucial for subsequent forging and final performance.

Ingot Homogenization Treatment:

The ingots undergo precisely controlled homogenization annealing (typically at 460-480°C for 24-48 hours) to eliminate macrosegregation, dissolve coarse secondary phases, and improve the ingot’s ductility, preparing it for subsequent high-deformation forging.

Billet Preparation and Inspection:

Ingot surface conditioning (scalping or milling) to remove all surface defects.

100% ultrasonic inspection is performed to ensure the ingot is free of any internal defects (e.g., cracks, porosity, large inclusions) that could affect final performance, typically requiring AMS 2630 class AA, the highest standard in the aerospace industry.

Preheating: The billet is uniformly heated to the precise forging temperature range (typically 400-450°C) to ensure optimal ductility while avoiding incipient melting (solidus temperature).

Forging Sequence (Large Diameter Ring Forgings):

Upsetting and Pre-forging: Large ingots are subjected to multi-directional, multiple upsetting and drawing operations on large hydraulic presses to break down as-cast grains and form suitable preform shapes (e.g., disc or pancake). Sufficient deformation is ensured to achieve thorough grain refinement and densification.

Piercing: On large hydraulic presses, a preliminary ring structure is formed by piercing with dies or mandrels. This process further compacts the material and refines the microstructure.

Ring Rolling Formation: This critical ring rolling process is performed on large vertical ring rolling machines. Continuous radial and axial compression is applied to the ring preform by a main roll and a mandrel roll, continuously increasing the ring’s diameter while reducing its wall thickness and height. Ring rolling achieves significant plastic deformation, highly aligning the grain flow along the ring’s circumference, ensuring the highest circumferential strength, and excellent fatigue and fracture toughness.

Die Forging Finish (Optional): For rings with more complex shapes or extremely high dimensional accuracy requirements, final shaping can be performed on large die forging presses to achieve precise geometric dimensions and good surface finish.

Minimum Reduction Ratio: Typically requires at least 3:1 to ensure complete elimination of the as-cast structure and formation of optimized grain flow.

Heat Treatment:

Solution Heat Treatment: The forging is heated to a precise solutionizing temperature of approximately 475-485°C and held for sufficient time to fully dissolve alloying elements (Zn, Mg, Cu) into the aluminum matrix, forming a uniform solid solution. Temperature uniformity is controlled within ±3°C.

Quenching: Rapid cooling from the solutionizing temperature (typically water quenching, with water temperature controlled below 60°C) to retain the supersaturated solid solution. Quenching speed is critical for final properties, ensuring uniform cooling for thick-section rings.

Aging Treatment:

T73 Temper: Two-stage or multi-stage overaging treatment (e.g., first stage 107°C/4-6 hours, second stage 165°C/8-12 hours). This treatment produces coarser and more stable precipitates, significantly improving resistance to stress corrosion cracking (SCC) and exfoliation corrosion, with a slight sacrifice in strength.

T74 Temper: Similar to T73, typically performed at slightly higher temperatures or longer aging times, aiming to provide similar SCC resistance to T73 but with slightly higher strength.

T6 Temper (less common for thick-section 7050): Standard artificial aging, providing maximum strength, but with higher susceptibility to SCC and exfoliation corrosion in thick sections and large diameter forgings, generally not recommended.

Finishing & Inspection:

Deburring, straightening, dimensional inspection, surface quality checks.

Finally, comprehensive nondestructive testing (e.g., ultrasonic, penetrant, eddy current) and microstructural analysis are performed to ensure the product fully complies with aerospace and defense standards.

 

The mechanical properties of 7050 large diameter aluminum alloy forged rings depend on the specific thickness, heat treatment temper, and optimization of the forging process. T73 and T74 are the most commonly used tempers for thick-section 7050 due to their optimal balance between strength and corrosion resistance.

 

Property	T73 (Typical)	T74 (Typical)	Test Method
Ultimate Tensile Strength (UTS)	470-520 MPa	490-540 MPa	ASTM E8
Yield Strength (0.2% YS)	400-450 MPa	420-470 MPa	ASTM E8
Elongation (2 inch)	9-14%	8-13%	ASTM E8
Hardness (Brinell)	135-155 HB	145-165 HB	ASTM E10
Fatigue Strength (5×10⁷ Cycles)	150-180 MPa	160-190 MPa	ASTM E466
Fracture Toughness (K1C)	28-38 MPa√m	25-35 MPa√m	ASTM E399
Shear Strength	280-320 MPa	300-340 MPa	ASTM B769

 

Property Distribution and Anisotropy:

7050 forged rings, through precise ring rolling, have grain flow highly aligned along the ring’s circumference. Therefore, circumferential (tangential) properties (strength, fatigue, fracture toughness) are typically optimal. Radial and axial properties are relatively lower, but their values still far exceed many other alloys, and their degree of anisotropy is lower than extruded or rolled products.

Thickness Effect: 7050 alloy is particularly adept at maintaining its mechanical properties, including strength and fracture toughness, showing a significant advantage in thick-section applications (e.g., above 100mm), superior to 7075 alloy.

Core to Surface Hardness Variation: Through optimized quenching and aging processes, hardness variation is typically controlled within 5 HB, ensuring overall property uniformity.

Residual Stress: T7X51 or T7X52 tempers (stress relief by stretching or compression) are commonly used to significantly reduce quenching residual stress, minimize machining distortion, and improve SCC resistance.

 

The microstructure of 7050 large diameter aluminum alloy forged rings is the cornerstone of their high strength and excellent corrosion resistance, with particular emphasis on grain morphology, precipitate phases, and defect control.

Key Microstructural Features:

Grain Structure and Grain Flow:

Fine, uniform recrystallized grains and elongated non-recrystallized grains aligned along the forging direction.

Grain Flow: During ring rolling, grains are heavily elongated and form a continuous fibrous structure along the ring’s circumference. This grain flow highly matches the main stress direction of the ring, significantly improving circumferential strength, fatigue life, and fracture toughness.

Dispersoids: Fine Al₃Zr dispersoids (approx. 50-100nm) formed by Zirconium (Zr) pin grain boundaries and within grains, effectively inhibiting recrystallization and grain growth, ensuring a fine-grained microstructure while providing some strengthening.

ASTM grain size is typically 6-8 or finer.

Strengthening Phase (Precipitate) Distribution:

The primary strengthening phase in 7050 is the zinc and magnesium-rich MgZn₂ (η phase) precipitate.

T73/T74 overaging treatments lead to coarser and more uniform, discontinuous η phases, especially with optimized precipitate morphology at grain boundaries, which effectively reduces the tendency for intergranular crack propagation, thereby significantly improving resistance to stress corrosion cracking (SCC) and exfoliation corrosion.

Precipitate-Free Zones (PFZ): The width of precipitate-free zones along grain boundaries is strictly controlled to balance strength with toughness/SCC resistance.

High Density and Defect Elimination:

The immense pressure applied during the forging process completely closes internal defects, such as porosity, shrinkage cavities, and gas pockets, that may arise during casting, significantly improving the material’s density and reliability.

Effectively breaks down and uniformly disperses small amounts of primary intermetallic compounds and impurities (e.g., Fe, Si phases), reducing their detrimental effects.

Metallurgical Cleanliness:

Aerospace-grade melting and casting technologies ensure extremely low non-metallic inclusion content, meeting the most stringent cleanliness requirements.

 

 

 

The size range of 7050 large diameter aluminum alloy forged rings is very wide and can be custom-produced according to the strict requirements of aerospace, military, and other sectors.

 

Parameter	Typical Manufacturing Range	Precision Tolerance (Usually after Machining)	Commercial Tolerance (As-Forged)	Test Method
Outer Diameter	500-5000+ mm	±0.1 mm to ±0.5 mm	±1.0 mm to ±5 mm	CMM
Inner Diameter	400-4900+ mm	±0.1 mm to ±0.5 mm	±1.0 mm to ±5 mm	CMM
Wall Thickness	50-800+ mm	±0.1 mm to ±0.5 mm	±1.0 mm to ±5 mm	CMM
Height	50-1200+ mm	±0.1 mm to ±0.5 mm	±1.0 mm to ±5 mm	CMM
Flatness	N/A	0.1 mm/meter diameter	0.5 mm/meter diameter	Flatness Gauge/CMM
Concentricity	N/A	0.1 mm	0.5 mm	Concentricity Gauge/CMM
Surface Roughness	N/A	Ra 3.2 μm max	Ra 12.5 μm max	Profilometer

 

Customization Capability:

Custom-made forged rings with various sizes, shapes, and tolerance requirements can be produced according to detailed customer drawings and technical specifications.

Typically offered in Rough Machined or Finish Machined conditions to ensure ease and precision of subsequent processing.

Extremely high demands for dimensional accuracy and surface quality, usually requiring strict machining after forging.

 

7050 alloy primarily achieves its excellent mechanical properties through heat treatment.

 

Temper Code	Process Description	Optimal Applications	Key Characteristics
O	Fully annealed, softened	Intermediate state before further processing	Maximum ductility, lowest strength, easy for cold working
T6	Solution heat treated, then artificially aged	Non-thick sections or non-SCC-sensitive applications	Highest strength, but high SCC and exfoliation sensitivity in thick sections
T73	Solution heat treated, then overaged (two-stage or multi-stage)	Aerospace thick-section structural components	Excellent resistance to stress corrosion cracking and exfoliation, high fracture toughness, slightly lower strength than T6
T74	Solution heat treated, then overaged (similar to T73, potentially slightly higher strength)	Aerospace thick-section structural components	Balances high strength with excellent SCC/exfoliation resistance, slightly better overall than T73
T76	Solution heat treated, then specially aged	Certain applications requiring specific strength and SCC balance	Good overall properties, high stress corrosion resistance

 

Temper Selection Guidance:

T73/T74 Tempers: The preferred tempers for large diameter 7050 forged rings. They provide excellent resistance to stress corrosion cracking (SCC) and exfoliation corrosion while maintaining high strength, which is crucial for safety-critical aerospace applications. T74 typically offers slightly higher strength than T73.

T6 Temper: Not recommended for thick-section or SCC-sensitive applications due to significantly lower SCC and exfoliation corrosion resistance compared to T73/T74.

Residual Stress Relief:

TXX51: Solution heat treated, followed by at least 1.5% stretching for stress relief, then aged. This is an effective method for eliminating quenching residual stress, significantly reducing machining distortion.

TXX52: Solution heat treated, followed by compression for stress relief, then aged. Suitable for complex shapes or large components where stretching is not feasible.

 

Machining 7050 large diameter aluminum alloy forged rings requires high-performance machine tools, specialized tooling, and strict process control to handle its high strength and potential residual stresses.

 

Operation	Tool Material	Recommended Parameters	Comments
Turning	Carbide, PCD	Vc=150-500 m/min, f=0.1-0.4 mm/rev	High-rigidity machine tools, large positive rake angle tools, attention to chip management
Drilling	Carbide, TiN/DLC coated	Vc=50-150 m/min, f=0.08-0.3 mm/rev	Sharp cutting edges, high helix angle, through-coolant preferred, prevents built-up edge
Milling	Carbide, HSS	Vc=200-700 m/min, fz=0.05-0.2 mm	Large positive rake angle, ample chip clearance, avoid vibration
Tapping	HSS-E-PM, TiCN coated	Vc=15-30 m/min	Proper lubrication, prevents thread tearing
Grinding	Aluminum oxide, CBN wheels	Use with caution, strict control, can induce residual stress and surface burning	Typically avoided, turning and milling are preferred
Welding	Not Recommended	Fusion welding causes significant strength loss and reduced corrosion resistance	Solid-state joining techniques like Friction Stir Welding (FSW) may be considered

 

Fabrication Guidance:

Machinability: 7050 alloy generally has good machinability, but cutting forces are relatively high, and long, stringy chips can be generated. Requires sharp tools, large rake angles, ample cooling and lubrication, and an efficient chip evacuation system.

Residual Stress: Quenched 7050 forgings have significant residual stresses. TXX51/TXX52 treatments effectively reduce these. During machining, strategies like symmetric machining and multi-pass shallow cuts should be employed to minimize distortion.

Surface Treatment:

Anodizing: Type II (sulfuric) or Type III (hard) is recommended, providing wear resistance, corrosion resistance, and insulation. Hard anodizing significantly improves surface hardness and wear resistance.

Conversion Coatings: Chromate or chromium-free conversion coatings serve as excellent primers for paint.

Coatings: Applied in aerospace applications to provide additional protection and functionality.

Weldability: Conventional fusion welding of 7050 alloy is poor, leading to significant strength loss and susceptibility to hot cracking and porosity. Fusion welding is generally not recommended. If joining is necessary, solid-state joining techniques like Friction Stir Welding (FSW) or mechanical fastening should be considered.

 

The corrosion resistance of 7050 alloy, particularly its resistance to stress corrosion cracking (SCC) and exfoliation corrosion, is a key characteristic distinguishing it from other high-strength aluminum alloys.

 

Corrosion Type	T73 (Typical)	T74 (Typical)	Protection System
Atmospheric Corrosion	Good	Good	Anodizing, coating
Seawater Corrosion	Good	Good	Anodizing, coating, galvanic isolation
Stress Corrosion Cracking (SCC)	Excellent	Excellent	T73/T74 temper inherently provides excellent resistance
Exfoliation Corrosion	Excellent	Excellent	T73/T74 temper inherently provides excellent resistance
Intergranular Corrosion	Low Susceptibility	Low Susceptibility	Heat treatment control

 

Corrosion Protection Strategies:

Temper Selection: T73 or T74 tempers are crucial for 7050 alloy to provide optimal SCC and exfoliation corrosion resistance.

Surface Treatment:

Anodizing: The most common protection method for aerospace aluminum alloys, forming a dense oxide film that enhances corrosion and wear resistance.

Chemical Conversion Coatings: Serve as excellent primers for paints or adhesives.

Coating Systems: High-performance primer and topcoat systems are used, especially in corrosive environments.

Galvanic Corrosion Management: When in contact with incompatible metals, isolation measures such as coatings, gaskets, or sacrificial anodes must be employed.

 

Property	Value	Design Consideration
Density	2.83 g/cm³	Lightweight design, center of gravity control
Melting Range	477-635°C	Heat treatment and solidus temperature
Thermal Conductivity	150 W/m·K	Thermal management, heat dissipation design
Electrical Conductivity	30% IACS	Electrical conductivity in electrical applications
Specific Heat	860 J/kg·K	Thermal mass and heat capacity calculations
Thermal Expansion (CTE)	23.4 ×10⁻⁶/K	Dimensional changes due to temperature variations
Young’s Modulus	72.4 GPa	Deflection and stiffness calculations
Poisson’s Ratio	0.33	Structural analysis parameter
Damping Capacity	Moderate-Low	Vibration and noise control

 

Design Considerations:

Extreme Strength-to-Weight Ratio: 7050 is one of the strongest aluminum alloys, and combined with its relatively low density, it is an ideal choice for extreme lightweighting in structural components, a core requirement in aerospace.

Excellent Fracture Toughness: Maintains high toughness even in thick sections, improving the damage tolerance and safety margin of structures.

Superior Stress Corrosion Cracking (SCC) and Exfoliation Corrosion Resistance: Provides higher reliability and longer service life in complex service environments.

Optimized Fatigue Performance: Forged grain flow and dense microstructure significantly extend fatigue life.

Good Dimensional Stability: Through TXX51/TXX52 treatments, residual stress is minimized, ensuring dimensional stability during processing and in-service use.

Extremely High Reliability: Rigorous control over melting, forging, and heat treatment, along with comprehensive non-destructive testing, ensures minimal internal defects in the material.

 

Quality control for 7050 large diameter aluminum alloy forged rings is among the most stringent for aerospace-grade products, ensuring the highest level of reliability and safety.

Standard Testing Procedures:

Raw Material Certification: Strict chemical composition analysis to ensure compliance with AMS, ASTM, etc., and full traceability of heat numbers, production dates, etc.

Melting and Casting Process Control: Hydrogen content, cleanliness (assessed by standards like SEP 1920/1940 or DDA-P9TF40), ingot microstructural uniformity (macro-segregation, grain size).

Forging Process Monitoring: Real-time monitoring of forging temperature, pressure, deformation amount, and deformation rate to ensure grain refinement and grain flow formation.

Heat Treatment Process Monitoring: Furnace temperature uniformity (AMS 2750E), solutionizing temperature and time, quenching rate, aging curve, etc., often using thermocouples to directly measure part temperature.

Chemical Composition Analysis: Spectrometer, XRF, etc., to verify all alloying elements and impurity content.

Mechanical Property Testing:

Tensile Testing: Samples taken in multiple directions (radial, tangential/circumferential, and axial), testing UTS, YS, EL. Typically, samples are taken from inner, middle, and outer radii and different heights of the ring.

Hardness Testing: Brinell, Rockwell hardness, etc., multi-point measurements to assess uniformity.

Impact Testing: For cryogenic or toughness-sensitive applications.

Fatigue Testing: Rotating bending fatigue, axial fatigue, or crack growth rate (da/dN) testing, assessing fatigue life and damage tolerance.

Fracture Toughness Testing: K1C value, typically using CT (compact tension) or SENB (single edge notch bend) specimens depending on thickness, rigorously assessing resistance to crack propagation.

Stress Corrosion Cracking (SCC) Testing: C-ring test (ASTM G38), Slow Strain Rate Test (SSRT, ASTM G129), or loaded beam test (ASTM G44) to verify SCC resistance of T73/T74 tempers.

Exfoliation Corrosion Testing: EXCO test (ASTM G34) to verify exfoliation corrosion resistance.

Nondestructive Testing (NDT):

Ultrasonic Testing: 100% volumetric inspection, typically required to meet AMS 2630 class AA or SAE ARP 1924 Level A, the most critical method for detecting internal defects (e.g., inclusions, micro-cracks, porosity).

Penetrant Testing: Detects surface-breaking defects (AMS 2645).

Eddy Current Testing: Detects surface and near-surface defects.

Radiographic Testing: For re-inspection of internal defects in specific critical areas.

Microstructural Analysis: Metallographic examination to assess grain size, grain flow, degree of recrystallization, precipitate morphology and distribution, defect types, etc.

Dimensional and Surface Quality Inspection: Precise measurements using Coordinate Measuring Machines (CMMs), laser scanners, profilometers, etc.

Standards and Certifications:

Conforms to SAE AMS 4108 (7050 Aluminum Forgings), AMS 4109 (7050-T7452), AMS 2630 (Ultrasonic Inspection), ASTM B247, ISO, EN, GB/T, and other aerospace and industry standards.

Quality Management System Certifications: AS9100 (Aerospace), ISO 9001.

EN 10204 Type 3.1 or 3.2 Material Test Reports can be provided, and third-party certification can be arranged upon customer request.

 

7050 large diameter aluminum alloy forged rings are indispensable critical structural components in high-end fields such as aerospace and defense.

Primary Application Areas:

Aerospace:

Aircraft engine casings, turbine component rings, fan blade root connection rings, structural frame rings

Landing gear structural rings, fuselage bulkheads, door frames

Rocket and missile connection rings, interstage rings, structural reinforcement rings

Critical structural rings for satellites and space stations

Defense and Military:

Large artillery gun mounts, turret bearing races

High-performance military vehicle load-bearing rings, marine vessel structural rings

High-End Industrial:

Precision rings in semiconductor manufacturing equipment

Large high-speed rotating machinery components

Certain specialized equipment requiring extremely high strength, toughness, and reliability

Design Advantages:

Ultimate Strength-to-Weight Ratio: Providing the highest strength while achieving extreme lightweighting of structural components, a core requirement in the aerospace industry.

Excellent Fracture Toughness: Maintains high toughness even in thick sections, improving the damage tolerance and safety margin of structures.

Superior Stress Corrosion Cracking (SCC) and Exfoliation Corrosion Resistance: Provides higher reliability and longer service life in complex service environments.

Optimized Fatigue Performance: Forged grain flow and dense microstructure significantly extend fatigue life.

Good Dimensional Stability: Through TXX51/TXX52 treatments, residual stress is minimized, ensuring dimensional stability during processing and use.

Extremely High Reliability: Through stringent melting, forging, and heat treatment control, and comprehensive non-destructive testing, minimal internal defects are ensured in the material.

Design Limitations:

High Cost: Due to complex manufacturing processes, expensive raw materials, and strict quality control, the cost of 7050 forgings is significantly higher than other aluminum alloys.

Poor Weldability: Conventional fusion welding is not recommended; mechanical joining or riveting is typically used. Solid-state joining techniques (e.g., FSW) are limited options.

High-Temperature Performance: Aluminum alloys generally do not withstand high temperatures well. 7050’s strength will significantly decrease with long-term use above 120°C.

Machining Challenges: While machinability is good, high strength means high cutting forces, requiring high-rigidity machine tools and specialized tooling, and attention to residual stress control.

Economic and Sustainability Considerations:

Total Life Cycle Cost: Despite significant initial investment, the ultra-high performance and long lifespan of 7050 forgings in critical aerospace components significantly reduce total life cycle costs, including maintenance, replacement, and fuel consumption. Its value far exceeds the material cost.

Material Utilization: Forging, as a near-net shape process, helps reduce raw material waste.

Environmental Impact: Aluminum alloys are highly recyclable, aligning with sustainable development principles. The energy-saving and emission-reduction effects of lightweighting are significant.