In the aerospace industry, where precision, safety, and efficiency define every engineering decision, the choice of materials plays a vital role. From the aircraft’s structure to its fuel delivery system, every component must meet stringent standards for strength, corrosion resistance, and reliability.
Among the wide range of aluminum alloys used in aviation, 5251 aluminum tube has become one of the preferred materials for aircraft fuel systems. Its unique balance of mechanical strength, corrosion resistance, light weight, and formability makes it exceptionally suitable for critical fluid-handling applications in modern aircraft.
In this article, SASAALUMINUM explains in detail why 5251 aluminum tube is preferred for aircraft fuel systems, exploring its key characteristics, performance advantages, and comparison with other aerospace alloys.
1. Overview of 5251 Aluminum Alloy
5251 aluminum alloy belongs to the 5xxx series (Al-Mg) group — non-heat-treatable alloys primarily strengthened by magnesium. Known for excellent corrosion resistance, moderate strength, and superb formability, it is ideal for aerospace components that operate under pressure or exposure to fluids such as aviation fuel, hydraulic oil, and lubricants.
General Properties
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Medium strength (higher than 5052, lower than 5083)
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Excellent resistance to seawater, fuel, and industrial chemicals
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High ductility and good weldability
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Non-heat-treatable; strengthened through cold working
Because of these balanced characteristics, 5251 aluminum is widely used for aircraft fuel tubes, hydraulic lines, and tank structures, where reliability under cyclic stress is crucial.
2. Chemical Composition of 5251 Aluminum
| Element | Content (%) | Function |
|---|---|---|
| Magnesium (Mg) | 1.7 – 2.8 | Strength and corrosion resistance |
| Silicon (Si) | ≤ 0.40 | Improves fluidity during fabrication |
| Iron (Fe) | ≤ 0.50 | Impurity control |
| Copper (Cu) | ≤ 0.15 | Slight increase in strength |
| Manganese (Mn) | 0.10 – 0.50 | Improves ductility and toughness |
| Chromium (Cr) | ≤ 0.15 | Increases resistance to stress corrosion |
| Zinc (Zn) | ≤ 0.15 | Minor strengthening |
| Titanium (Ti) | ≤ 0.15 | Grain refinement for uniformity |
| Aluminum (Al) | Balance | Base element |
This composition provides a clean, stable, and corrosion-resistant alloy, ensuring safe performance in contact with aviation fuels and hydraulic fluids.
3. Mechanical Properties of 5251 Aluminum Tube
The mechanical strength of 5251 depends on its temper condition, but even in its standard states, it offers an excellent balance of strength and ductility — critical for fuel system tubing.
| Property | Typical Value (H14 Temper) | Unit |
|---|---|---|
| Tensile Strength | 210 – 250 | MPa |
| Yield Strength (0.2% Proof) | 130 – 160 | MPa |
| Elongation (in 50mm) | 10 – 12 | % |
| Modulus of Elasticity | 70 | GPa |
| Hardness | 65 – 75 | HB |
| Density | 2.68 | g/cm³ |
| Fatigue Strength | 100 – 120 | MPa |
These properties ensure that 5251 aluminum tubes can handle both static loads and cyclic stresses common in aircraft fuel systems without fatigue or fracture.
4. Key Advantages for Aircraft Fuel Systems
There are several critical reasons why 5251 aluminum tubes are widely used in aviation fuel lines:
1. Excellent Corrosion Resistance
Fuel systems are exposed to various types of fuels (Jet A, kerosene, gasoline) and moisture condensation. 5251’s magnesium-enriched surface film provides outstanding corrosion resistance even when exposed to aggressive fuels and additives.
Unlike some heat-treatable alloys (e.g., 6061), 5251 does not suffer from intergranular corrosion or stress-corrosion cracking, ensuring long-term reliability in demanding environments.
2. Lightweight and High Strength-to-Weight Ratio
Aircraft performance depends heavily on weight reduction. 5251 aluminum offers high specific strength (strength per unit weight), making it ideal for minimizing aircraft mass while maintaining structural integrity.
A tube made from 5251 aluminum is roughly one-third the weight of a comparable steel tube, resulting in improved fuel efficiency and payload capacity.
3. Excellent Formability and Bendability
Aircraft fuel lines often require complex routing through confined fuselage spaces and around components. The ductility of 5251 aluminum allows it to be easily bent, flared, and shaped without cracking or losing wall thickness.
This characteristic simplifies manufacturing, reduces assembly time, and ensures precision fitment in tight aircraft structures.
4. Superior Weldability
5251 aluminum can be welded using TIG (GTAW) or MIG (GMAW) processes with minimal risk of cracking or porosity. The alloy maintains its corrosion resistance after welding, unlike some heat-treated alloys that lose protection due to microstructural changes.
This makes it highly suitable for welded joints, fittings, and connectors within fuel systems where airtight sealing is essential.
5. Resistance to Aviation Fuels and Additives
Modern aviation fuels often contain chemical additives (such as anti-icing agents and corrosion inhibitors). 5251’s surface oxide layer resists reaction with hydrocarbons and maintains chemical stability, preventing contamination or degradation over time.
6. Fatigue Resistance Under Vibration
Aircraft experience continuous vibration during flight. 5251 aluminum exhibits excellent fatigue resistance, allowing it to withstand thousands of takeoff and landing cycles without cracking. This ensures long service life for fuel lines and minimizes maintenance downtime.
5. Comparison with Other Alloys Used in Fuel Systems
| Property | 5251 Aluminum | 6061 Aluminum | 5052 Aluminum | Steel (304) |
|---|---|---|---|---|
| Strength | Medium | High | Medium | Very High |
| Density (g/cm³) | 2.68 | 2.70 | 2.68 | 7.90 |
| Corrosion Resistance | Excellent | Good | Excellent | Fair |
| Weldability | Excellent | Good | Excellent | Moderate |
| Formability | Excellent | Moderate | Excellent | Poor |
| Cost | Moderate | Moderate | Low | High |
| Typical Use | Aircraft fuel tubes | Structural parts | Fuel tanks | Hydraulic lines |
Summary
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5251: Ideal for fuel systems — balance of light weight, corrosion resistance, and formability.
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6061: Stronger but more rigid; not as flexible for bending complex tube shapes.
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5052: Similar corrosion resistance but lower mechanical strength.
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Steel: Very strong but too heavy for aerospace applications.
6. Thermal and Chemical Stability
Aircraft fuel lines must perform across a wide temperature range — from sub-zero at altitude to high temperatures near engines.
Thermal Properties of 5251 Aluminum
| Property | Value |
|---|---|
| Melting Range | 580 – 650°C |
| Coefficient of Thermal Expansion | 24 × 10⁻⁶ /°C |
| Thermal Conductivity | 134 – 147 W/m·K |
The alloy’s low thermal expansion ensures dimensional stability and tight sealing even under rapid temperature fluctuations, while its high conductivity allows efficient dissipation of heat from fuel transfer operations.
7. Safety and Reliability in Aviation Applications
Safety is the most critical aspect of aerospace design. 5251 aluminum contributes to safer aircraft operation through:
1. Leak Prevention
The material’s smooth surface finish and weld integrity ensure leak-free joints and connections in pressurized systems.
2. Chemical Compatibility
Compatible with aviation fuels, lubricants, and hydraulic fluids, 5251 aluminum prevents contamination or reaction during long-term service.
3. Resistance to Stress Corrosion
Magnesium alloys like 5251 exhibit exceptional resistance to stress corrosion cracking (SCC), even in humid or chemically aggressive environments. This is vital in aircraft where failure could lead to catastrophic results.
8. Standards and Certifications
Aerospace-grade 5251 aluminum tubes supplied by SASAALUMINUM conform to international quality and performance standards.
| Standard | Description |
|---|---|
| ASTM B210 | Seamless aluminum and aluminum-alloy drawn tubes |
| EN AW-5251 | European designation for 5251 alloy |
| BS 1474 | Extruded aluminum and aluminum-alloy products |
| ISO 6362-2 | Wrought aluminum mechanical property specifications |
| EN 10204 3.1 | Mill test certificate verification |
Each batch is tested for mechanical strength, dimensional accuracy, and corrosion resistance, ensuring compliance with aerospace specifications.
9. Real-World Applications of 5251 Aluminum Tubes in Aviation
5251 aluminum tubing is used in various parts of an aircraft fuel system, including:
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Fuel Supply Lines – Transferring fuel from tanks to engines with consistent flow and minimal pressure drop.
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Vent and Drain Lines – Resistant to corrosion and fluid contamination.
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Fuel Tank Structures – Providing lightweight, durable containment for aviation fuel.
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Hydraulic and Pneumatic Tubes – Shared material standards due to pressure and corrosion similarities.
These applications demonstrate 5251’s versatility and reliability in multiple aerospace subsystems.
10. Comparison: 5251 vs 6061 in Aircraft Tubing
| Criteria | 5251 | 6061 |
|---|---|---|
| Temper Options | O, H14, H24 | T4, T6 |
| Strength | Medium | High |
| Ductility | Excellent | Moderate |
| Corrosion Resistance | Excellent | Good |
| Weldability | Excellent | Very Good |
| Fatigue Resistance | High | High |
| Typical Use | Fuel and hydraulic lines | Structural tubing and fittings |
Although 6061 aluminum is stronger, 5251 is preferred in fuel systems because of its superior flexibility and resistance to corrosion — qualities more important than extreme strength in fluid systems.
11. Maintenance and Longevity
Because of its natural oxide film and chemical stability, 5251 aluminum requires minimal maintenance. In aircraft maintenance schedules, fuel lines made of 5251 generally have service intervals twice as long as those made from lower-grade materials.
Additionally:
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Surface anodizing or alodine treatment can further extend life span.
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Tubes remain visually clean and structurally intact even after thousands of flight hours.
12. Environmental Benefits
Lightweight materials like 5251 aluminum contribute to lower fuel consumption and reduced carbon emissions in aviation. Its recyclability also supports the global push for sustainable aircraft manufacturing.
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Recyclable Rate: Over 90%
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Energy Savings: Recycling aluminum requires 95% less energy than producing primary aluminum.
Thus, using 5251 in aircraft fuel systems aligns with the industry’s environmental and economic sustainability goals.
13. Why Choose SASAALUMINUM
As a leading manufacturer and supplier of high-performance aluminum materials, SASAALUMINUM provides certified 5251 aerospace aluminum tubes engineered to meet the demanding requirements of modern aircraft manufacturers and maintenance centers.
Our Advantages
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Certified Quality: All products supplied with EN 10204 3.1 mill test certificates.
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Extensive Stock: Seamless and welded tubes available in multiple diameters and tempers.
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Precision Processing: CNC cutting, forming, and surface finishing available.
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Global Supply Network: Fast delivery to aerospace clients worldwide.
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Technical Expertise: Engineering support for alloy selection and design optimization.
With its commitment to quality and innovation, SASAALUMINUM ensures reliable material solutions for critical aerospace applications.
14. Summary of Key Advantages
| Feature | Benefit in Aircraft Fuel Systems |
|---|---|
| Corrosion Resistance | Prevents degradation from fuels and moisture |
| Formability | Easy to bend and shape for complex routing |
| Weldability | Strong, leak-free joints |
| Strength-to-Weight Ratio | Lightweight efficiency without sacrificing strength |
| Fatigue Resistance | Long service life under cyclic stress |
| Chemical Stability | Compatible with aviation fuels and additives |
15. Conclusion
The aerospace industry demands materials that combine strength, safety, and reliability under extreme conditions. 5251 aluminum tube fulfills these demands perfectly — offering an ideal blend of lightweight design, corrosion resistance, weldability, and durability.
In aircraft fuel systems, where safety and performance are paramount, 5251 aluminum provides the perfect solution: it resists corrosion from aviation fuels, maintains integrity under vibration, and offers outstanding formability for complex fuel line routing.
With decades of industry experience and global expertise, SASAALUMINUM continues to deliver high-quality 5251 aluminum tubes that power the aerospace sector’s most critical systems — ensuring precision, performance, and safety at every altitude.
Post time: Oct-28-2025