Aluminium Alloys in the Aerospace Industry

By Marta Danylenko of Matmatch

Aluminium has a long and successful history in the aerospace industry. As far back as the 19th century, Count Ferdinand Zeppelin made the frames of his iconic airships from it. Aluminium was chosen as it is lightweight, strong and has a high resistance to corrosion. This article explains the common alloys used in aerospace engineering and their applications, as well as some less well-known ones, and what the future holds for aerospace materials.

A Brief History

The Wright brothers chose aluminium for the cylinder block and other engine parts for their first manned flight in 1903. It was also the first time an aluminium alloy had been heat-strengthened. This discovery prompted the preference for aluminium in aerospace engineering.

Over the years, the aerospace industry has become more demanding in terms of material requirements. The advent of jumbo jets and long-haul international flights meant that the shell and engine parts had to be extremely durable and resistant to fatigue. This has led to the development and use of many different types of aluminium alloys.

Common Aluminium Alloys in Aerospace

Second only to AA 2024 in terms of its popularity in aerospace engineering, AA2014 is a strong and tough metal and is suitable for arc and resistance welding. However, it has poor corrosion resistance, and for that reason, it is often found in the internal structure or framework of aircraft rather than the shell.

Aluminium alloy 2024 is probably the most widely used alloy for aircraft. It was developed after experiments allowing small amounts of cold deformation and a period of natural ageing led to an increased yield strength. 2024 is a high-grade alloy with excellent fatigue resistance. It’s used primarily in sheet forms such as for the fuselage and wings due to its high tensile strength of roughly 470 MPa.

Of the non-heat treatable grades of alloy, AA 5052 provides the highest strength and is highly ductile, so it can be formed into a variety of shapes including engine components and fittings. It is also highly corrosion resistant.

AA 6061 alloy is very common in light aircraft, especially homemade ones. It’s easily welded and manipulated, is very light and fairly strong, making it ideal for fuselage and wings.

AA 7050 has high corrosion resistance and maintains strength in wide sections. This makes it more resistant to fractures than other alloys. It’s commonly used in wing skins and fuselage, especially in military aircraft.

AA 7068 is the strongest alloy available today. Combined with its low mass, it is suitable for military aircraft that need to stand up to tough conditions and attacks.

With similar strength properties to steel due to its high levels of zinc, AA 7075 has fatigue resistance. It can be machined easily, which meant it was a popular choice for fighter planes in World War II, including the Mitsubishi A6M Zero fighter used by the Japanese Imperial Navy on their carriers between 1940 and 1945. It is still used frequently in military aircraft to this day.

Less Common Aluminium Alloys in Aerospace

If you need an aluminium alloy that provides maximum strength at elevated temperatures, AA 2219 is the best bet. It was used for the external fuel tank of the first successfully launched space shuttle, Columbia. It has good weldability, but the welds need heat-treating to preserve resistance against corrosion.

AA 6063 is mainly used for aesthetic and architectural finishes and can be found in the finer details of an aircraft. It is used primarily for intricate extrusions. AA 7475 is highly resistant to fracture and fatigue. Due to its toughness, it is sometimes found in fuselage bulkheads of larger aircraft.

The Future of Aluminium Alloys in Aerospace

Industry experts are positive about the future of aluminium alloys in aerospace. It is projected that demand for aluminium will double over the next decade.

By 2025, there will be a global demand of 80 million tonnes. For this reason, the aerospace industry is increasingly looking to recycled alloys to satisfy their high demand. There is also a push for innovation in the materials used, as well as the design structure of aircraft.

For instance, aluminum-lithium alloys have been developed for the aerospace industry to reduce the weight of aircraft and therefore improve performance of the aircraft. Al-Lithium alloys are advanced materials because of their low density, high specific modulus, and excellent fatigue and cryogenic toughness properties.

As developing countries become more involved in the aerospace industry, and with increased investment, there will be further innovation in aluminium alloys over the years to come.

Marta Danylenko is marketing manager at Matmatch, an online materials database.