Aviation aluminum: characteristics

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 of the alloy is given by the so-called. "Aging effect" is a special method of hardening under the influence of an aggressive atmospheric environment for a long time. The alloy was invented at the beginning of the 20th century, dirural, and is now also known as the "avial".

Definition. Historical digression

The beginning of the history of aviation aluminum alloys is 1909. German metallurgical engineer Alfred Wilm has experimentally established that if an alloy of aluminum with a slight addition of copper, manganese and magnesium is quenched at 500 ° C and quenched at a temperature of 20-25 degrees for 4-5 days, it gradually becomes harder and Stronger, without losing plasticity. The procedure was called "aging" or "maturity". In the process of this hardening, copper atoms fill a multitude of tiny zones at the grain boundaries. The diameter of the copper atom is smaller than that of aluminum, so a compressive stress appears, which increases the strength of the material.

For the first time the alloy was mastered at the German plants Dürener Metallwerken and received the trademark Dural, hence the name "duralumin". Subsequently, American metallurgists R. Archer and V. Jafris improved the composition, changing the percentage, mainly magnesium. The new alloy was named 2024, which in various modifications is widely used now, and the entire family of alloys - Avial. The name "aviation aluminum" was obtained almost immediately after the discovery, since it completely replaced the wood and metal in the aircraft structures.

Main types and characteristics

There are three main groups:

• Families of aluminum-manganese (Al-Mn) and aluminum-magnesium (Al-Mg). The main characteristic - high, hardly conceding to pure aluminum corrosion resistance. Such alloys are well suited for soldering and welding, but they are badly cut. Do not harden by heat treatment.
• Corrosion-resistant alloys of the aluminum-magnesium-silicon (Al-Mg-Si) system. They are strengthened by thermal treatment, namely quenching at a temperature of 520 ° C followed by a sharp cooling of water and natural aging for about 10 days. A distinctive characteristic of the materials of this group is the high corrosion resistance in operation under normal conditions and under stress.
• Structural alloys of aluminum-copper-magnesium (Al-Cu-Mg). Their basis 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 differ.

The materials of the latter group have good mechanical properties, but are highly prone to corrosion than the first and second family of alloys. The degree of corrosion susceptibility depends on the kind of surface treatment that still needs to be protected by paint or anodizing. Corrosion resistance is partially increased by introducing manganese into the composition.

In addition to the three main types of alloys, forging alloys, heat-resistant, high-strength structural, and others possessing properties that are necessary for a particular field of application are also distinguished.

Marking of aviation alloys

In international standards, the first figure for the marking of aviation aluminum indicates the main alloying elements of the alloy:

• 1000 - pure aluminum.
• 2000 - duralumin, alloys doped with copper. In a certain period - the most common aerospace alloy. Due to the high sensitivity to corrosion cracking, they are increasingly replaced with 7000 series alloys.
• 3000 - alloying element - manganese.
• 4000 - alloying element - silicon. Alloys are also known as silumin.
• 5000 - alloying element - magnesium.
• 6000 - the most plastic alloys. Alloying elements are magnesium and silicon. Can be subjected to heat cracking to increase strength, but this parameter is inferior to the 2000 and 7000 series.
• 7000 - thermally hardened alloys, the most durable aviation 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 initial one - the digit "0". The two final figures are the number of the alloy itself, information about its purity by impurities. If the alloy is experienced, a fifth sign "X" is added to the marking.

To date, the most common brands of aviation aluminum: 1100, 2014, 2017, 3003, 2024, 2219, 2025, 5052, 5056. The distinctive features of these alloys are: lightness, ductility, good strength, resistance to friction, corrosion and high loads. In aircraft building, the most widely used alloys are aviation aluminum 6061 and 7075.

Composition

The main alloying elements of aviation aluminum are: copper, magnesium, silicon, manganese, zinc. The percentage of these elements by mass in the alloy determine such characteristics as strength, flexibility, resistance to mechanical influences, etc. The basis of the alloy is aluminum, the main alloying elements are copper (2.2-5.2% by weight), magnesium (0, 2-2.7%) and manganese (0.2-1%).

A family of aviation alloys of aluminum with silicon (4-13% of mass) with insignificant content of other alloying elements - copper, manganese, magnesium, zinc, titanium, beryllium. Used for the manufacture of complex parts, also known as silumin or foundry aluminum alloy. A family of aluminum-magnesium alloys (1-13% by weight) with other elements possess high plasticity and corrosion resistance.

The role of copper in aviation aluminum

The presence of copper in the composition of an aviation alloy contributes to its hardening, but at the same time, it does not have a good effect on its corrosion resistance. Falling along the grain boundaries, during the hardening process, copper makes the alloy prone to pitting corrosion, stress corrosion and intergranular corrosion. Areas rich in copper are more galvanically cathodic than the aluminum matrix around, and therefore are more vulnerable to corrosion occurring on the galvanic mechanism. An increase in the copper content in the alloy mass up to 12% increases the strength properties due to dispersive hardening in the aging process. With a copper content of more than 12%, the alloy becomes brittle.

Applications

Aluminum alloys are the most popular metal for sale. The light weight of aviation aluminum, durability make this alloy a good choice for many productions from aircraft to household items (mobile phones, headphones, flashlights). Aluminum alloys are used in shipbuilding, automotive, construction, rail transport, in the nuclear industry.

Widespread demand for alloys with a moderate content of copper (2014, 2024 others). Profiles of these alloys have high corrosion resistance, good machinability, and spot weldability. Of these, responsible structures of aircraft, heavy vehicles, military equipment are manufactured.

Features of aviation aluminum connection

Welding of aviation alloys is carried out exclusively in the protective environment of inert gases. Preferred gases are: helium, argon or a mixture thereof. Helium is more highly conductive. This determines the more favorable temperature characteristics of the welding medium, which makes it possible to connect the thick-walled elements of the structures quite comfortably. The use of a mixture of protective gases promotes a more complete gas outflow. The probability of formation of pores in the welded joint is significantly reduced.

Application in aircraft construction

Aviation aluminum alloys were originally created for the construction of aviation equipment. Of them, the hulls of aircrafts, engine parts, chassis, fuel tanks, fastening devices, etc. are made of aviation aluminum parts in the interior of the cabin.

Aluminum alloys of the 2ххх 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 alloys 3xxx, 5xxx and 6xxx. The most widely used in aircraft construction was alloy 7075. It produces elements for work under considerable load, low temperatures with high resistance to corrosion. The basis of the alloy is aluminum, and the main alloying elements are magnesium, zinc and copper. From it are made the power profiles of aircraft structures, elements of skin.