Due to its lightness, ductility and corrosion resistance, aluminum has become an indispensable material in many industries. Aviation aluminum is a group of alloys characterized by increased strength with the inclusion of magnesium, silicon, copper and manganese. Additional strength is given to the alloy using the so-called. “Aging effect” is a special method of hardening under the influence of aggressive atmospheric environment for a long time. The alloy was invented at the beginning of the 20th century, called duralumin, now also known as "air".
Definition Historical excursion
The beginning of the history of aviation aluminum alloys is considered to be 1909. The German metallurgical engineer Alfred Wilm experimentally established that if an aluminum alloy with a slight addition of copper, manganese and magnesium after quenching at a temperature of 500 ° C and rapid cooling can withstand at a temperature of 20-25 degrees for 4-5 days, it gradually becomes harder and stronger, without losing plasticity. The procedure is called "aging" or "maturity." In the process of such quenching, copper atoms fill many tiny zones at the grain boundaries. The diameter of the copper atom is smaller than that of aluminum, therefore, a compression stress appears, as a result of which the strength of the material increases.
For the first time the alloy was mastered at the German Dürener Metallwerken factories and received the Dural trademark, whence the name "duralumin" came from. Subsequently, American metal experts R. Archer and W. Jaffries improved the composition by changing the percentage, mainly magnesium. The new alloy was called 2024, which is widely used in various versions now, and the entire alloy family is Avial. The name "aviation aluminum" this alloy received almost immediately after the opening, since it completely replaced wood and metal in the construction of aircraft.
Main types and characteristics
There are three main groups:
- The families are aluminum-manganese (Al-Mn) and aluminum-magnesium (Al-Mg). The main characteristic is high corrosion resistance, barely inferior to pure aluminum. Such alloys lend themselves well to soldering and welding, but are poorly cut. Not hardened by heat treatment.
- Corrosion-resistant alloys of the aluminum-magnesium-silicon system (Al-Mg-Si). Hardened by heat treatment, namely hardening at a temperature of 520 ° C, followed by rapid cooling with water and natural aging for about 10 days. A distinctive characteristic of materials of this group is high corrosion resistance during operation under ordinary conditions and under voltage.
- Structural alloys aluminum-copper-magnesium (Al-Cu-Mg). Their base is aluminum alloyed with copper, manganese and magnesium. By changing the proportions of the alloying elements, aviation aluminum is obtained , the characteristics of which may vary.
Materials of the latter group have good mechanical properties, but are very susceptible to corrosion than the first and second family of alloys. The degree of susceptibility to corrosion depends on the type of surface treatment that still needs to be protected with paintwork or anodizing. Corrosion resistance is partially increased by the introduction of manganese into the alloy.
In addition to the three main types of alloys, forging alloys are also distinguished , heat-resistant, high-strength structural, etc., possessing the properties necessary for a particular application.
Marking Aviation Alloys
In international standards, the first digit of the marking of aviation aluminum indicates the main alloying elements of the alloy:
- 1000 - pure aluminum.
- 2000 - duralumin alloys alloyed with copper. In a certain period - the most common aerospace alloy. Due to their high sensitivity to corrosion cracking, they are increasingly being replaced by 7000 series alloys.
- 3000 - alloying element - manganese.
- 4000 - alloying element - silicon. Alloys are also known as silumins.
- 5000 - alloying element - magnesium.
- 6000 are the most ductile alloys. Alloying elements are magnesium and silicon. They can be thermally quenched to increase strength, but are inferior in this parameter to the 2000 and 7000 series.
- 7000 - thermally hardened alloys, the most durable aircraft aluminum. The main alloying elements are zinc and magnesium.
The second digit of the marking is the serial number of the modification of the aluminum alloy after the original - the number "0". Two final digits - the number of the alloy itself, information about its purity by impurities. If the alloy is experienced, the fifth “X” mark is added to the marking.
Today, the most common brands of aviation aluminum are: 1100, 2014, 2017, 3003, 2024, 2219, 2025, 5052, 5056. Distinctive features of these alloys are: lightness, ductility, good strength, resistance to abrasion, corrosion and high loads. In the aircraft industry, the most widely used alloys are aircraft aluminum 6061 and 7075.
Composition
The main alloying elements of aviation aluminum are: copper, magnesium, silicon, manganese, zinc. The percentage of these elements by weight in the alloy is determined by such characteristics as strength, flexibility, resistance to mechanical stress, etc. The basis of the alloy is aluminum, the main alloying elements: copper (2.2-5.2% of the mass), magnesium (0, 2-2.7%) and manganese (0.2-1%).
A family of aviation alloys of aluminum with silicon (4-13% by weight) with a low content of other alloying elements - copper, manganese, magnesium, zinc, titanium, beryllium. Used for the manufacture of complex parts, also known as silumin or cast aluminum alloy. The family of aluminum-magnesium alloys (1-13% by weight) with other elements have high ductility and corrosion resistance.
The role of copper in aviation aluminum
The presence of copper in the composition of the aviation alloy contributes to its hardening, but at the same time it has a bad effect on its corrosion resistance. Falling along the grain boundaries during the hardening process, copper makes the alloy susceptible to pitting, stress corrosion and intergranular corrosion. Zones rich in copper are more galvanically cathodic than the aluminum matrix around, and therefore more vulnerable to corrosion occurring by the galvanic mechanism. An increase in the copper content in the alloy mass to 12% increases the strength properties due to dispersed hardening during aging. With a copper content of over 12%, the alloy becomes brittle.
Fields of application
Aluminum alloys are the most sought-after metal for sale. The light weight of aircraft aluminum and its strength make this alloy a good choice for many industries from airplanes to household items (mobile phones, headphones, flashlights). Aluminum alloys are used in shipbuilding, automotive, construction, railway production, and in the nuclear industry.
Alloys with a moderate copper content are widely in demand (2014, 2024, etc.). Profiles of these alloys have high corrosion resistance, good machinability, spot weldability. Responsible structures of aircraft, heavy vehicles, and military equipment are made from them.
Features of joining aircraft aluminum
Welding of aircraft alloys is carried out exclusively in a protective environment of inert gases. Preferred gases are: helium, argon, or a mixture thereof. Helium has a higher thermal conductivity. This determines the more favorable temperature parameters of the welding medium, which allows you to quite comfortably connect thick-walled structural elements. The use of a mixture of protective gases contributes to a more complete gas vent. Moreover, the likelihood of pore formation in the weld is significantly reduced.
Application in the aircraft industry
Aviation aluminum alloys were originally specially created for the construction of aviation equipment. Aircraft bodies, engine parts, chassis, fuel tanks, fasteners, etc. are made from them. Aviation aluminum parts are used in the interior of the cabin.
Aluminum alloys of the 2xxx series are used for the production of parts exposed to high temperatures. Details of lightly loaded units, fuel, hydraulic and oil systems are made of 3xxx, 5xxx and 6xxx alloys. The most widely used in the aircraft industry was alloy 7075. Elements are made of it to work under significant loads, low temperatures, and high corrosion resistance. The basis of the alloy is aluminum, and the main alloying elements are magnesium, zinc and copper. Power profiles of aircraft structures, lining elements are made from it.