Aluminum alloys
Aluminum has a long and successful history in aerospace. As far back as the 19th century, Count Ferdinand Zeppelin used it to make the frames of his iconic airships, demonstrating aluminum’s light weight, strength, and high resistance to corrosion. More than a century later, it is the most-used metal in the air. Marta Danylenko, marketing manager at online materials database Matmatch, explains common aluminum alloys used in aerospace engineering and their applications, as well as some less well-known ones, and what the future holds for aerospace materials.
The Wright brothers chose aluminum for the cylinder block and other engine parts on their first manned flight in 1903. It was also the first time an aluminum alloy had been heat-strengthened, a discovery that positioned aluminum’s dominance in aerospace engineering.
Throughout the years, the aerospace industry has become more demanding in 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, leading to the development and use of many different aluminum alloys.
Second only to aluminum alloy 2024 in terms of its popularity in aerospace engineering, 2014 is a strong, tough metal suitable for arc and resistance welding. However, it has poor corrosion resistance, so it is often found in the internal structure or framework of aircraft rather than the shell.
Probably the most widely used alloy for aircraft, 2024 was developed after experiments allowing small amounts of cold deformation and a period of natural aging led to an increased yield strength. A high-grade alloy with excellent fatigue resistance, 2024 is used primarily in sheet forms such as for the fuselage and wings due to its high tensile strength of roughly 470MPa.
Of the non-heat treatable grades of alloy, 5052 provides the highest strength and is highly ductile, so it can be formed into various shapes. It is also highly corrosion resistant.
The 6061 aluminum alloy is common in light aircraft, especially homemade ones. Easily welded and manipulated, 6061 is very light and fairly strong, making it ideal for fuselage and wings.
Alloy 7050 has high corrosion resistance and maintains strength in wide sections, making it more resistant to fractures than other alloys. It’s commonly used in wing skins and fuselage, especially in military aircraft.
The strongest alloy available today, 7068’s strength and low mass make it perfect for military aircraft that must stand up to tough conditions and attacks.
With similar strength as steel due to its high levels of zinc, 7075 has excellent fatigue resistance. It can be machined easily, which made it 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.
The 2219 aluminum alloy provides maximum strength at elevated temperatures. It was used for the external fuel tank on the first successfully launched space shuttle, Columbia. It has good weldability, but the welds need heat-treating to preserve resistance against corrosion.
Found in the finer details of an aircraft, 6063 is mainly used for aesthetic and architectural finishes. It is used primarily for intricate extrusions. Highly resistant to fracture and fatigue due to its strength, 7475 is sometimes found in fuselage bulkheads of larger aircraft.
Industry experts have a positive outlook about the future of aluminum alloys in aerospace, projecting demand for aluminum will double during the next decade.
By the year 2025, there will be a global demand of 80 million metric tons, so, the aerospace industry is increasingly looking at recycled alloys to satisfy the high demand. There is also a push for innovation in the materials used, as well as the design structure of aircraft.
For instance, newly developed aluminum-lithium alloys could reduce the weight of aircraft and improve their performance. Aluminum-lithium alloys are advanced materials because of their low density, high specific modulus, and excellent fatigue and cryogenic toughness properties.