Where Are Aluminum Alloys Used in Aircraft?

The development of aluminum alloys has always been closely linked to aviation. The Wright brothers’ aircraft already used an Al-Cu-Mn casting for the engine crankcase in the early twentieth century. The discovery of age hardening in Al-Cu-Mg alloys in 1906 made aluminum-copper alloys practical primary structural materials for airframes.

Aviation alloy development has passed through several stages. In the 1950s, the main goals were lower weight and higher specific stiffness and strength. During the 1960s and 1970s, attention shifted to durability and damage tolerance, leading to T73 and T76 treatments for 7xxx alloys, alloy 7050, and high-purity alloys. Rising fuel prices drove further weight reduction in the 1980s. Since the 1990s, development has combined weight reduction with improved durability, damage tolerance, strength, toughness, and corrosion resistance. Thick plate with low residual stress also enables large integral structures to replace assemblies made from many parts, reducing weight while improving consistency.

Cast Aluminum Alloys for Aircraft

Modern aircraft contain roughly 1,500 to 2,000 types of aluminum-alloy castings. Three basic groups are selected according to service conditions and location:

• High-strength casting alloys: Mainly Al-Cu alloys made by sand casting. They are used for fuselage parts, engine compartments, seats, and control systems and can often replace aluminum die forgings.
• Heat-resistant casting alloys: Highly alloyed Al-Cu-Ni materials used near engines and in air-exchange systems at approximately 200 to 400°C, where resistance to thermal deformation is important.
• Corrosion-resistant casting alloys: Al-Mg alloys combining strength, ductility, impact toughness, fatigue resistance, and weldability. They are suitable for seaplane structures exposed to corrosive environments.

Wrought Aluminum Alloys for Aircraft

The most widely used wrought aviation materials include 2xxx Al-Cu alloys, 7xxx Al-Zn alloys, and Al-Li alloys. They are common in skins, wings, frames, floor beams, and other load-bearing structures.

Typical Applications of Al-Cu Alloys

The 2xxx series was the first heat-treatable aluminum-alloy family widely adopted in aviation.

Typical Applications of Al-Zn Alloys

The commercial 7xxx series contains some of the strongest wrought aluminum alloys. These materials offer high specific strength and stiffness, good corrosion and damage resistance, and good machinability. Over more than 90 years, development progressed from optimizing a single property to balancing overall performance, while product sizes grew substantially. Successive families include 7×75, 7×50/7010, 7055/7449, and 7136/7056 alloys.

Typical Applications of Al-Li Alloys

Lithium is the lightest metallic element, and its maximum solubility in aluminum is 4.2%. Adding 1% Li to an aluminum-alloy matrix can reduce density by about 3% and increase elastic modulus by about 5% to 6%. Compared with conventional high-strength 2xxx and 7xxx alloys, Al-Li alloys provide low density, high elastic modulus, high specific strength and modulus, a low fatigue-crack growth rate, and good high- and low-temperature performance. Compared with composites, they also retain advantages in impact resistance, ductility, and repairability.

Other Aluminum Alloys Used in Aircraft

Other series also have specialized roles. The source identifies 3003 and 5052 as common materials for tanks, pipes, and corrosion-resistant parts and identifies 5052 for skin framing. Its detailed application table uses the Chinese alloy designations 5A02 and 5A05.