What is aircraft aluminum? How is it used?

Building aircraft means choosing materials very carefully; the wrong choice can lead to big problems. You need materials that are strong yet light, and "aircraft aluminum" is often mentioned for this exact reason.

"Aircraft aluminum" refers to high-strength aluminum alloys¹, like 2024 and 7075, specifically developed for aerospace. It's used to build most of the aircraft's structure, including the fuselage, wings, and control surfaces, due to its excellent strength-to-weight ratio.

At SWA Forging, we've been working with many types of aluminum alloys since 2012, producing large-diameter forged rings and discs. While our direct clients are often traders and machining companies in sectors like industrial equipment or energy, not aerospace manufacturers, the principles of using high-quality, certified aluminum are the same. Understanding specialized materials like aircraft aluminum helps us appreciate the high standards required in demanding industries, which reinforces our own commitment to quality (backed by our ISO9001, ISO14001, and ISO45001 certifications).

How is aluminum used in aircraft?

You see an airplane and wonder what holds it all together up there. Much of what you see, and much of what you don't, is actually aluminum, playing a vital role.

Aluminum is used extensively in aircraft for structural components. This includes the fuselage skin and framework, wing structures (spars, ribs, skin), tail sections, engine nacelles, and control surfaces like ailerons and rudders.

When you look at a typical commercial or military aircraft, aluminum is everywhere. It's not just one part; it forms the backbone and the skin.
Let's break down some key areas:

• Fuselage: This is the main body of the aircraft. The outer skin, the internal frames (formers), and the longitudinal stiffeners (stringers) are very often made from high-strength aluminum alloys. These components must withstand pressurization loads, aerodynamic forces, and provide overall structural integrity.
• Wings: Aircraft wings are complex structures designed to generate lift. The main load-bearing components inside the wing, called spars (running spanwise) and ribs (running chordwise), are commonly made from aluminum. The wing skin, which needs to be smooth for aerodynamics and strong enough to carry loads, is also usually aluminum.
• Empennage (Tail Section): The vertical stabilizer (fin) and horizontal stabilizers, along with their control surfaces (rudder and elevators), are critical for stability and control. These are also typically constructed using aluminum alloys for their frames and skins.
• Other Components: You'll also find aluminum in engine nacelles (the housing around engines), landing gear components (though some very high-stress parts might be steel or titanium), and various brackets and fittings throughout the aircraft.
  The reason for this widespread use comes down to aluminum's ability to be formed into complex shapes, joined effectively (often by riveting in aerospace), and its overall performance characteristics. I've seen many complex aluminum forgings pass through our facility at SWA Forging, destined for demanding industrial uses, and the precision required reminds me of the tolerances needed in aerospace.

Why is aluminium used for making aircraft parts?

Aircraft need to be strong but also light enough to fly efficiently. Why did aluminum become the go-to metal for so many decades in aircraft manufacturing? This is a key question.

Aluminum is used for aircraft parts mainly because of its excellent strength-to-weight ratio. It's also relatively easy to fabricate, has good corrosion resistance (especially certain alloys or when treated), and is more cost-effective than alternatives like titanium or composites for many applications.

Several key properties make aluminum alloys so attractive for aircraft construction. It's not just one thing, but a combination.

Key Advantages of Aluminum in Aerospace:

1. High Strength-to-Weight Ratio: This is probably the most important factor. Aluminum alloys specifically designed for aerospace (like 7075-T6) can be very strong, almost like some steels, but they are only about one-third the weight. This lightness means aircraft can fly further, carry more payload, or use less fuel.
2. Formability and Machinability: Aluminum can be relatively easily formed into the complex aerodynamic shapes needed for aircraft skins and structures. It can be extruded into long sections, rolled into sheets, and forged into strong, near-net shape parts. It's also generally easier to machine than harder metals like titanium or high-strength steels. Our clients in machining appreciate the good machinability of the aluminum alloys we forge at SWA Forging.
3. Corrosion Resistance: While not immune to corrosion, many aluminum alloys have good natural corrosion resistance due to the formation of a protective oxide layer. Specific alloys are better than others, and additional treatments like anodizing, cladding (Alclad), or painting are used to enhance this, especially in harsh marine or industrial environments aircraft might operate in.
4. Fatigue Resistance: Certain aluminum alloys, like 2024-T3, are known for their good resistance to fatigue cracking, which is crucial for parts that experience repeated stress cycles during flight.
5. Cost-Effectiveness: Compared to other lightweight materials like titanium or advanced carbon fiber composites, aluminum is often more economical for many aircraft structures, both in terms of raw material cost and manufacturing costs.
   Even with the rise of composites, aluminum remains a dominant material in aircraft construction because of this strong combination of properties.

What is the composition of aircraft aluminium alloy?

You hear about "aircraft aluminum" like 2024 or 7075. What makes these alloys special? It's the specific elements added to the aluminum that give them their high performance.

Aircraft aluminum alloys have precise compositions. For example, 2024 is primarily alloyed with copper, while 7075's main alloying element is zinc, along with magnesium and copper. These additions, combined with heat treatment, create their high-strength properties.

Pure aluminum is relatively soft and not very strong. To achieve the high strength needed for aircraft, other elements are added in carefully controlled amounts. The specific "recipe" of these alloying elements, followed by specific heat treatments (tempers), defines the alloy's final properties.
Here's a look at some common aircraft alloys and their primary alloying elements:

• Copper (Cu): In the 2xxx series, copper significantly increases strength through precipitation hardening when heat-treated.
• Zinc (Zn): In the 7xxx series, zinc, usually with magnesium and copper, creates the highest strength aluminum alloys, also through precipitation hardening.
• Magnesium (Mg) & Silicon (Si): In the 6xxx series, these form magnesium silicide, which provides good strength after heat treatment, along with good formability and corrosion resistance.
• Magnesium (Mg): In the 5xxx series (not typically primary aircraft structure but used for other parts), magnesium provides good strength through solid solution strengthening and excellent corrosion resistance, especially in marine environments.
  Understanding these compositions is critical. At SWA Forging, we deal with a range of aluminum alloys for our forged rings and discs, and ensuring the correct chemical composition for each customer's specification is paramount. We provide product quality certificates for every order, and third-party certifications (SGS, BV, TUV) are available if our clients need them, confirming that the material meets all required standards.

Is aircraft aluminum stronger than steel?

When you think of strength, steel often comes to mind. So, how does aircraft aluminum compare? Is it actually stronger? The answer needs a bit of explanation.

Pound for pound (or kilogram for kilogram), high-strength aircraft aluminum alloys often offer a better strength-to-weight ratio than many steels. While some steels have higher absolute strength, aluminum's lower density means aircraft structures can be made lighter for a given strength requirement.

This question often causes confusion because "stronger" can be interpreted in different ways.

• Absolute Strength (e.g., Tensile Strength per unit area): If you take a rod of high-strength steel and a rod of high-strength aluminum of the exact same size, the steel rod will generally be able to withstand a higher load before breaking. For example, alloy steels can have ultimate tensile strengths well over 1000 MPa, while a strong aircraft aluminum like 7075-T6 might be around 570 MPa. So, by this measure, steel is "stronger."
• Strength-to-Weight Ratio (Specific Strength): This is where aluminum shines for aerospace. Aluminum's density is about 2.7 g/cm³, while steel's is around 7.8 g/cm³. Steel is roughly 2.9 times denser.
  To get the strength-to-weight ratio, you divide the strength by the density. Even though steel's absolute strength is higher, its much higher density means that high-strength aluminum alloys often come out ahead in specific strength. This means for a given weight, you can often build a stronger structure with aluminum, or for a given strength requirement, the aluminum structure will be significantly lighter.
  This is why I often emphasize to our clients at SWA Forging that material selection isn't just about one property; it's about the combination of properties relevant to the application. For an aircraft, minimizing weight while maintaining structural integrity is paramount. While some ultra-high-stress components in aircraft (like landing gear pins) might still use specialty steels, aluminum's superior strength-to-weight ratio makes it the primary choice for the bulk of the airframe.

Conclusion

Aircraft aluminum, like 2024 and 7075, is chosen for its superior strength-to-weight ratio. It's used widely in airframes because it's light, strong, and relatively easy to work with.