The history of world aviation is closely related to aluminium and the history of creating aluminium alloys, and the more durable and reliable aluminium became, the higher, farther and safer airplanes flew. But, before it became the essential and most important material for aircraft manufacturers, aluminium navigated a long route from pure metal to high-strength alloys.
The first person who managed to understand the potential of aluminium in the aerospace industry was the writer Jules Verne, who provided a detailed description of an aluminium rocket in his fantastic novel ‘Journey to the Moon’ in 1865. In 1903, the Wright brothers got the first airplane off the ground, in which parts of the engine were made of aluminium.
‘Aircraft’ aluminium appeared for the first time in Germany in the early 20th century. At that time, it was just starting to ‘come into vogue’. The technology of its industrial production had already been perfected, but the amounts of smelt metal were still small. Many scientists then set themselves the goal to solve the task of aluminium reinforcement. Among them was Alfred Wilm, a German physicist. During his experiments on selecting components for aluminium reinforcement, unexpectedly for himself and the entire scientific community, he discovered the ‘aging effect’ of the aluminium alloy, which consists in the considerable improvement of metal strength after its quenching for a long period. Alfred Wilm’s discovery was patented and implemented in production at Duerener Metallwerke AG plant. In 1909, the plant officially presented its products: the ultra-strong alloy, duralumin (aluminium, copper (1.3%), magnesium (2.8%) and manganese (1%)). In fact, this metal became the base for development of aircraft alloys.
The advantages of Duerener ‘aluminium’ were appreciated by Professor of Thermal Dynamics, and Aircraft Manufacturer of Aachen University, Hugo Junkers. More than once he attempted to assemble an all-metal airplane: On December 15th, 1915 testing of the J1 glider made of sheet iron was held at the military airfield of Deberitsa. But the representatives of the military administration ‘rejected’ the airplane, calling it ‘a tin donkey’: J1 – too heavy, with a low climbing capacity and manoeuvrability, and did not comply with the requirements of military aviation. Junkers understood that the major ‘culprit’ of the failure was metal. He needed an alternative to thick (up to 1 mm) iron sheets. And this alternative was found!
Duralumin met all the requirements of Hugo Junkers: high strength, forgeability, and the incredible lightness for a metal were very much to the point. As soon as in 1917, the J.7 fighter entirely built of the ‘light’ metal took off from Adlershof airfield.
In the same year, production of Junk J.1 military airplanes was started; they were ordered by the German Ministry of Defence for participation in the First World War campaigns. During the military campaign, duralumin completely proved Junkers’ calculations: The metal reliably protected the pilot from bullets and shells. Junk J.1 airplanes were named ‘flying tanks’. There is a recorded case when duralumin sustained 480 bullet shots on the wings and fuselage, and the airplane not only completed the combat mission, but also successfully landed at base.
The success of the first J.7 and Junk J.1 airplanes predetermined the breakthrough in the development of German military aviation. Duralumin became the favourite of Junkers’ design department. Germany won the battle for the sky, however its rivals were not going to surrender, and developments of ultra-strong aluminium alloys were in full swing in the USSR and USA.
In 1918, on the insistence of the manufacturer A.N. Tupolev and Professor of Moscow State University N.E. Zhoukovsky, the Central Aerohydrodynamics Institute (CAHI) was established, where development of new models of airplanes and metal alloy studies were started. CAHI worked in collaboration with some smelters, which allowed them to promptly receive and test new metals. However, for as many as four years the efforts of the researchers were in vain: The created alloys could not pass the strength test.
At that time, developments of wooden airplanes were underway in Soviet Russia, many of which were quite successful. The government of the country treated the idea of launching metal into the sky half heartedly: Aluminium was imported into the country, and the German manufacturers devoutly guarded the secret of duralumin.
In Spring 1922, a significant event happened at CAHI: The fuselage of a shot-down Junkers D.I fighter – a priceless trophy from the viewpoint of domestic aviation – was delivered to the Institute. A separate ‘Material Testing Division’ group was organised, in order to study the composition of the airplane metal covering. The researchers did not just determine the formula of duralumin but managed to develop a stronger alloy modification, able to compete with foreign developments. The results of their work were sent to the Brass and Copper-Rolling Plant of Kolchougin Co. and the Leningrad plant ‘Krasny Vyborzhets.’
The first to master the production of this domestic know-how were the metallurgists of the Kolchougin plant: In late 1922, the plant started production of ‘kolchougaluminium’ – the first Soviet high-strength alloy. And as soon as the following year, Tupolev’s design department was provided with the complete ‘aircraft’ set: sheet, corrugated, and shaped kolchougaluminium. Work was started to create a competitor to Junkers, the Soviet airplane AN-2, which was presented on May 28th, 1924.
Aluminium played an important role during the Second World War. The invaluable contribution in establishing the defence power of the Soviet Army was made by the Urals Aluminium Smelter (UAZ). The first stage of UAZ was commissioned in September 1939. On the eve of the war, 36% of aluminium produced in the country was produced there. High-strength duralumin sheets and slabs served as the main material for airplane covering. Complex-preformed blocks were produced from them to make component parts of airplane engines, propellers, the chassis, and the fuselage frame. Soft low-alloy duralumin and aluminium-magnesium alloys were used for rolling wire for rivets, covering connective elements; sheets of aluminium-manganese alloy were used for welding fuel tanks. Without magnesium and aluminium powders, it was impossible to produce bombs, shells, and flares.
At present, aluminium is used in the aviation industry everywhere in the world. From two thirds to three quarters of a passenger plane’s dry weight, and from one twentieth to half of a rocket’s dry weight accounts for the share of aluminium in airborne craft. The casing of the first Soviet satellite was made of aluminium alloys. The body casing of American ‘Avantgarde’ and ‘Titan’ rockets used for launching the first American rockets into the orbit, and later on – spaceships, was also made of aluminium alloys. They are used for manufacturing various components of spaceship equipment: brackets, fixtures, chassis, covers and casing for many tools and devices.
2xxx, 3xxx, 5xxx, 6xxx, and 7xxx series alloys are widely used in aviation. The 2xxx series is recommended for operation at high working temperatures and with high destruction viscosity rates. 7xxx series alloys – for operation at lower temperatures of highly-loaded parts and for parts with high resistance to corrosion under stress. For less loaded components, 3xxx, 5xxx, and 6xxx series alloys are used. They are also used in hydraulic, oil and fuel systems.
Aluminium alloys have a certain advantage for creating space equipment units. High values of specific strength, and the specific rigidity of the material enabled the tanks, inter-tank and casing of the rocket to be manufactured with high longitudinal stability. The advantages of aluminium alloys (2219 etc.) also include their high performance under cryogen temperatures in contact with liquid oxygen, hydrogen, and helium. The so-called cryogen reinforcement happens in these alloys, i.e. the strength and flexibility increase parallel to the decreasing temperature.
Engineers and manufacturers never cease to study the properties of aluminium, developing more and more new alloys for construction of aircraft and spaceships. Who knows, maybe, what the modern science-fiction books write about will be realised very soon.