In the aerospace and transportation industries, aluminum alloys play an essential role due to their unique combination of lightweight, strength, corrosion resistance, and workability. Among the many aluminum grades used in structural and aircraft manufacturing, 5251 aluminum alloy is one of the most versatile and reliable choices.
This alloy, particularly when used in aerospace aluminum tubes, offers a strong balance between mechanical performance and ease of fabrication. In this article, SASAALUMINUM provides a comprehensive overview of the mechanical properties of 5251 aerospace aluminum tube, along with its composition, temper options, applications, and advantages.
1. Introduction to 5251 Aluminum Alloy
Aluminum Alloy 5251 belongs to the 5xxx series of aluminum-magnesium alloys, which are known for their excellent corrosion resistance, moderate to high strength, and exceptional weldability.
The 5251 alloy is non-heat-treatable, meaning that its strength is achieved through cold working rather than thermal hardening. It offers good formability and medium static strength, making it particularly suitable for aerospace tube components, marine structures, and vehicle frames.
Key Features of 5251 Aluminum
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Excellent corrosion resistance, even in marine and humid environments
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Good ductility and formability, suitable for bending and rolling
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Medium mechanical strength with high fatigue resistance
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Excellent anodizing and polishing characteristics
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Non-heat-treatable, but hardens through work strain
These properties make it a preferred choice in aircraft systems, fluid transfer lines, and structural tubing.
2. Chemical Composition of 5251 Aluminum Alloy
The chemical composition of 5251 alloy defines its performance characteristics, particularly its balance between strength and corrosion resistance.
| Element | Content (%) | Function |
|---|---|---|
| Magnesium (Mg) | 1.7 – 2.8 | Provides strength and corrosion resistance |
| Silicon (Si) | ≤ 0.40 | Improves fluidity and machinability |
| Iron (Fe) | ≤ 0.50 | Impurity control |
| Copper (Cu) | ≤ 0.15 | Enhances mechanical strength slightly |
| Manganese (Mn) | 0.10 – 0.50 | Improves tensile strength |
| Chromium (Cr) | ≤ 0.15 | Increases hardness and corrosion resistance |
| Zinc (Zn) | ≤ 0.15 | Minor strengthening effect |
| Titanium (Ti) | ≤ 0.15 | Grain refinement |
| Aluminum (Al) | Balance | Base material |
This well-balanced chemical structure gives 5251 aluminum tubes their characteristic strength, weldability, and resilience against corrosion in various environments.
3. Mechanical Properties of 5251 Aerospace Aluminum Tube
The mechanical properties of 5251 aluminum depend on its temper condition — how much it has been cold-worked. Below are the standard values typically observed for aerospace-grade tubing.
| Property | O (Annealed) | H14 (Half-Hard) | H24 (Quarter-Hard) |
|---|---|---|---|
| Tensile Strength | 190 MPa | 210–250 MPa | 230–260 MPa |
| Yield Strength (0.2% Proof) | 80 MPa | 130–160 MPa | 150–180 MPa |
| Elongation (in 50mm) | 25–30% | 10–12% | 8–10% |
| Modulus of Elasticity | 70 GPa | 70 GPa | 70 GPa |
| Shear Strength | 115 MPa | 145 MPa | 155 MPa |
| Hardness (Brinell HB) | 45 | 65–75 | 75–85 |
| Density | 2.68 g/cm³ | 2.68 g/cm³ | 2.68 g/cm³ |
Key Observations
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The H14 temper provides an excellent combination of strength and ductility, ideal for aerospace tubing.
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The O temper is softer and more formable, used for deep drawing or complex shaping.
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The H24 temper offers higher rigidity and strength for load-bearing aerospace structures.
Thus, 5251 aluminum tubes can be tailored for both flexible and rigid aerospace applications depending on the temper used.
4. Strength-to-Weight Ratio Advantage
A major advantage of 5251 aerospace aluminum tube lies in its excellent strength-to-weight ratio. With a density of only 2.68 g/cm³, it provides significant weight reduction compared to steels or copper alloys.
Lightweight materials are crucial in aerospace design, where reducing every kilogram translates directly into improved fuel efficiency, payload capacity, and performance.
5. Fatigue and Toughness Properties
Fatigue Strength
5251 aluminum demonstrates strong fatigue resistance, particularly in cyclic loading conditions common in aircraft operations. Its fatigue strength is typically 100–120 MPa under reversed stress.
Fracture Toughness
The alloy exhibits good fracture toughness, allowing it to absorb impact energy without cracking. This makes it suitable for pressurized fluid systems, frames, and airframe brackets that experience repeated vibration and stress.
6. Corrosion and Environmental Resistance
The magnesium content of 5251 gives it exceptional natural protection against atmospheric, seawater, and chemical corrosion. It forms a stable oxide film on its surface that resists degradation even in salt-laden air.
In aerospace service, this resistance helps protect critical tubing systems such as:
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Hydraulic and pneumatic lines
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Air conditioning and cooling ducts
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Fuel and lubrication systems
For further durability, 5251 aluminum can be anodized or chemically treated to increase surface hardness and extend component lifespan.
7. Thermal and Electrical Properties
| Property | Value |
|---|---|
| Melting Range | 580–650°C |
| Thermal Conductivity | 134–147 W/m·K |
| Coefficient of Thermal Expansion | 24.0 × 10⁻⁶ /K |
| Electrical Conductivity | 33–35% IACS |
The high thermal conductivity makes 5251 suitable for heat exchangers and temperature-regulating aerospace systems, while its low thermal expansion ensures dimensional stability under wide temperature fluctuations.
8. Fabrication and Welding Characteristics
Formability
5251 aluminum is extremely formable, particularly in the annealed (O) condition. Tubes can be bent, flared, and expanded without risk of cracking, which is vital for aircraft systems that require precise routing through limited spaces.
Weldability
This alloy is highly weldable using TIG, MIG, or resistance welding techniques. Unlike many high-strength aluminum alloys, 5251 retains much of its corrosion resistance and strength after welding.
Machinability
While not as easy to machine as 6000-series alloys, 5251 can still be machined efficiently with sharp tools and proper coolant application. Its surface finish is smooth and uniform, suitable for decorative or aerodynamic components.
9. Temper Designations for Aerospace Use
Different tempers are used for specific aerospace applications of 5251 tubes.
| Temper | Description | Application |
|---|---|---|
| O (Annealed) | Soft, fully annealed for deep forming | Hydraulic tubing, custom fittings |
| H14 (Half-Hard) | Cold-worked, good balance of strength and formability | Structural and pressurized tubing |
| H24 (Quarter-Hard) | Higher strength, reduced ductility | Support frames, aerospace panels |
Choosing the right temper is crucial for balancing strength, flexibility, and fabrication efficiency in aerospace systems.
10. Comparison: 5251 vs 6061 vs 5083
| Property | 5251 | 6061 | 5083 |
|---|---|---|---|
| Series | 5xxx | 6xxx | 5xxx |
| Strength | Medium | High | High |
| Corrosion Resistance | Excellent | Good | Excellent |
| Weldability | Excellent | Very Good | Good |
| Machinability | Fair | Good | Moderate |
| Heat Treatable | No | Yes | No |
| Typical Use | Aerospace tubing, marine, automotive | Structural frames, fittings | Shipbuilding, cryogenic tanks |
Key takeaway:
5251 provides a balance between strength and corrosion resistance, making it more adaptable than 6061 for thin-wall aerospace tubes where flexibility and oxidation protection are key.
11. Aerospace Applications of 5251 Aluminum Tubes
5251 aluminum tubes are widely used in aircraft manufacturing and aerospace support systems. Common applications include:
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Hydraulic and Fuel Tubing
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Used for internal fluid transfer systems due to high corrosion resistance.
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Airframe Structures
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Lightweight yet durable, ideal for non-load-bearing structural parts.
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Cooling and Ventilation Systems
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Excellent thermal conductivity for efficient heat management.
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Aircraft Interiors
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Decorative and protective tubing with smooth anodized finishes.
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Landing Gear and Auxiliary Systems
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Reliable fatigue resistance under vibration and pressure cycles.
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The versatility of SASAALUMINUM 5251 aerospace tubes makes them suitable for both structural and fluid-handling applications in modern aircraft designs.
12. Advantages of 5251 Aerospace Aluminum Tube
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Excellent Corrosion Resistance
Perfect for long-term exposure to moisture, fuel, and hydraulic fluids. -
Medium Strength with High Ductility
Allows easy forming and shaping without cracking. -
Lightweight Efficiency
Enhances overall aircraft performance by reducing total system weight. -
Superior Weldability
Maintains structural integrity after joining operations. -
Good Surface Finish and Aesthetic Appearance
Suitable for visible interior components and aerodynamic designs. -
Cost-Effective
Provides a high-performance alternative to more expensive aerospace alloys.
13. Quality Assurance and Standards
SASAALUMINUM supplies 5251 aluminum tubes that conform to international aerospace and material standards, ensuring precision, consistency, and reliability.
Typical Standards
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ASTM B210 – Aluminum and aluminum-alloy seamless drawn tubes
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BS EN 754-8 – Cold drawn aluminum tubes
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EN AW-5251 – European designation for aluminum-magnesium alloy
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ISO 6362-2 – Mechanical properties of wrought aluminum products
All materials are supplied with EN 10204 3.1 Mill Test Certificates, verifying chemical composition and mechanical performance.
14. Why Choose SASAALUMINUM
As a trusted global supplier of aerospace-grade aluminum products, SASAALUMINUM provides high-quality 5251 aluminum tubes with superior precision and surface finish.
Our Advantages
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Certified Quality – Full traceability and compliance with ASTM, EN, and ISO standards.
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Wide Range of Sizes – Available in seamless and welded tubes from small diameters to large structural sizes.
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Customized Processing – Precision cutting, bending, and surface finishing to customer specifications.
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Technical Expertise – Engineering support for aerospace, marine, and industrial applications.
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Global Supply Chain – Reliable delivery to more than 40 countries worldwide.
SASAALUMINUM is committed to providing performance-driven aluminum solutions for the global aerospace industry.
15. Summary of Key Mechanical Properties
| Property | Typical Range | Unit |
|---|---|---|
| Tensile Strength | 210–250 | MPa |
| Yield Strength | 130–160 | MPa |
| Elongation | 10–12 | % |
| Modulus of Elasticity | 70 | GPa |
| Shear Strength | 145 | MPa |
| Hardness | 65–75 | HB |
| Fatigue Strength | 100–120 | MPa |
| Density | 2.68 | g/cm³ |
| Thermal Conductivity | 134–147 | W/m·K |
16. Conclusion
5251 Aerospace Aluminum Tube is a versatile and reliable material for modern aircraft construction and aerospace systems. With its medium strength, excellent corrosion resistance, high ductility, and exceptional weldability, it bridges the gap between lightweight design and structural integrity.
Whether used in hydraulic lines, heat exchangers, or airframe components, 5251 aluminum alloy provides long-lasting performance under demanding conditions.
Through strict quality control and engineering expertise, SASAALUMINUM continues to deliver precision-engineered 5251 aluminum tubes that meet the evolving needs of global aerospace manufacturers — ensuring strength, safety, and efficiency at every altitude.
Post time: Oct-28-2025