Metallurgy has played a key role in the development of aviation. With the discovery of new materials, new applications have been found to apply these too and to vastly improve existing designs.
Aluminum seems to be the king in aircraft construction, though in recent years some new alloys have been applied. These super alloys are still quite expensive for the aircraft homebuilder. With its good strength to weight and cost ratio, aluminum is still used very widely in the industry.
Current developments indicate that more and more manufacturers (Boeing, Airbus) are using carbon fiber and other non-metallic materials in aircraft construction as these can be made in almost any form and curvature. As time goes by these materials will have to prove themselves to be as reliable as aluminum in resisting UV damage. Proper application of UV resisting paint will help too.
Alcoa is developing an 3rd generation aluminum-lithium alloy which promises even more weight reduction and cost savings without the need for protection against lightning strikes as is the case in composite intensive aircraft.
Aluminum alloys are identified by a four digit numbering system. The first digit gives the alloy group and the others the alloys that are present in the mix. Below we have compiled a list of the most commonly used aircraft aluminum alloys and their respective properties.
The use of Copper (Cu) and Zinc (Zi) in an alloy with aluminum changes its properties in such a way that the alloy can be hardened as well as softened by the use of heat. The resulting temper designation is indicated by a letter number combination following the alloy numbers.
The most common temper designations we find are T3 and T6. T3 is solution heat-treated and cold-worked by the flattening process. T6 is also solution heat-treated but artificially aged.
Every alloy has its own properties depending on the composition of the alloying elements, for example 2024 alloy has 4.5 % Copper (Cu), 0.6 % Manganese (Mn) and 1.5 % Magnesium (Mg) added. 6061 has 0.25 % Copper, 0.6 % Silicon (Si), 1.0 % Magnesium and 0.25 % Chromium (Ch) added and 5052 is 2.5 % Magnesium and 0.25 % Chromium. The 3003 alloy has only 1.2 % of Manganese added.
The mechanical properties of an alloy are an important factor in the decision where to use it during construction. In the list below we give some typical properties:
This is the most common of the the high-strength aluminum alloys. It is high grade aircraft quality. 2024-T3 aluminum sheet is thought of as the aircraft alloy because of its strength and it also has excellent fatigue resistance. Corrosion resistance is less than 6061, hence the alclad versions. Welding is generally not recommended. Typical uses for 2024-T3 Alclad aluminum sheet are fuselage and wing skins, cowls, aircraft structures and also for repair and restoration because of its really shiny finish (2024-T3 Alclad). Its ultimate strength is 62000 PSI with a shearing strength of 40000 PSI.
This alloy has a very good corrosion resistance and finishing ability, welding goes without any problems too. The strength level of 6061-T6 aluminum sheet is about that of mild steel. 6061-T6 aluminum sheet can be fabricated by most of the commonly used techniques. Typical uses are aircraft landing mats, truck bodies and frames, structural components and more. Ultimate strength is 45000 PSI with a shearing strength of 30000 PSI.
This one has the highest strength in the NON-heatable alloy series. It is not structural. 5052 aluminum sheet has higher fatigue strength than most alloys. 5052 aluminum sheet has excellent corrosion resistance, particularly in marine applications and has excellent workability. This aluminum sheet is commonly used to construct fuel tanks.
Most widely used of aluminum alloys, pure aluminum with manganese added for strength, approx 20% stronger than the 100 series. 3003-H14 aluminum sheet has great workability and may be deep drawn, spun, welded or brazed. 3003 aluminum sheet is NON-heat treatable. This aluminum sheet is widely used for cowls and baffle plating. Ultimate strength is 21000 PSI with a shearing strength of 14000 PSI.
Aircraft manufacturers use high-strength alloys (principally alloy 7075) to strengthen aluminum aircraft structures. Aluminum alloy 7075 has Copper (1.6 %), Magnesium (2.5 %) and Zinc (5.6 %) added for ultimate strength, but the copper content makes it very difficult to weld. On the other hand it anodizes really beautifully. 7075 has the best machinability and it will result in a very nice finish. Ultimate strength is 33000 PSI (-0) and 82000 PSI (-T6) with a shearing strength of 22000 PSI (-0) and 49000 PSI (-T6).