In industrial production aluminum use became irreplaceable for a long time that is connected with its practical parameters. Ease, resistance to influence of the hostile external environment and plasticity do it by base metal and in aircraft industry. And modern aviation aluminum is alloy (group of alloys) in which except a basic component can join magnesium, copper, manganese or silicon. Besides, these alloys are exposed to a special technique of training which is called effect of aging. And now the alloy (duralumin) invented at the beginning of the 20th century is better known as "авиаль".
History of aviation aluminum originates in 1909. Then the German engineer Alfred Vilm could invent technology at which aluminum develops the increased hardness and strength when maintaining the plasticity. For this purpose he added a small amount of copper, magnesium and manganese to basic metal and began to temper the received connection at a temperature of 500 °C. Further it subjected aluminum alloy to sharp cooling at a temperature of 20-25 °C within 4-5 days. Personalized this stage-by-stage crystallization of metal also received the name of "ageing". And scientific justification to this technique is based that the size of atoms of copper is less than aluminum analogs. The additional tension of compression which provides the increased durability appears from behind it in molecular communications of aluminum alloys.
The Dural brand was appropriated at the German plants Dürener Metallwerken from where there was a name "duralyumin". Subsequently Americans R. Archer and V. Dzhafris improved aluminum alloy due to change of a magnesium ratio in it, having called it modification of 2024. And all group of aluminum alloys received the name "avial" that is connected first of all with the sphere of its application which is focused first of all on production of aircraft.
Types and characteristics of aviation aluminum
In aviation aluminum there are three groups of alloys.
The aluminum-manganese Al-Mn and Al-Mg differ in high resistance to the corrosion which almost is not inferior on this indicator to pure aluminum. They perfectly give in to welding and soldering, however are badly cut. And heat treatment practically cannot make them stronger.
The aluminum-magnesium-silicon Al-Mg-Si have the increased corrosive firmness (under normal operating conditions and energized) and improve the strength characteristics due to heat treatment. And training is made at a temperature of 520 °C. And the effect of aging is reached due to cooling in water and crystallization within 10 days.
The aluminum-copper-magnesium Al-Cu-Mg are considered as constructional alloys. Due to change of the elements alloying aluminum it is possible to vary also characteristics of the most aviation aluminum.
Thus, the first two groups of alloys have the increased resistance to corrosion, and the third differs in great mechanical properties. And additional protection against corrosion of aviation aluminum can be carried out by special processing of a surface (anodizing or paint coating).
Except the above-stated groups of alloys also constructional, heat resisting, forging and other types of aviation aluminum which as much as possible correspond to the sphere of the application are applied.
Marking and structure
The international system of standardization means special marking of aviation aluminum.
The first figure of the four-digit code designates the alloying alloy elements:
- 1 – pure aluminum;
- 2 – copper (this space alloy begins to be replaced with pure aluminum because of its high sensitivity to cracking today);
- 3 – manganese;
- 4 – silicon (alloys are alpaxes);
- 5 – magnesium;
- 6 – the magnesium and silicon (alloying elements provide the highest plasticity of alloys, and their thermal training increases strength characteristics);
- 7 – zinc and magnesium (the strongest alloy of aviation aluminum is exposed, temperature training).
The second figure of marking of aluminum alloy designates serial number of modification ("0" - initial number).
Two last figures of aviation aluminum contain information on number of alloy and its purity on impurity.
In case aluminum alloy still is in skilled development, the fifth sign "X" is added to its marking.
Now the following is considered as the most popular grades of aluminum alloys: 1100, 2014, 2017, 3003, 2024, 2219, 2025, 5052, 5056. They are characterized by special ease, durability, plasticity, resistance to mechanical influences and corrosion. And the aircraft manufacturing sphere the greatest distribution was received by aluminum alloys of brands 6061 and 7075.
Copper, magnesium, silicon, manganese and zinc are a part of aviation aluminum as the alloying elements. The percentage in alloy determines its flexibility, durability, resistance to various influences by the mass of these chemical elements.
So, in aviation aluminum a basis of alloy is aluminum, and copper (2.2-5.2%), magnesium (0.2-2.7%) and manganese (0.2-1%) act as the main alloying elements. Foundry aluminum alloy (alpax) in which the basic alloying element is silicon (4-13%) is applied to production of the most difficult details. Except it copper, magnesium, manganese, zinc, titanium and beryllium are the chemical composition of alpax in small proportions. And the group of aluminum alloys of the aluminum-magnesium family (Mg to 13% of lump) differs from 1% in special plasticity and resistance to corrosion.
For production of aviation aluminum as the alloying element copper is of particular importance. It gives to alloy the increased durability, however reduces resistance to corrosion as drops out on borders of grains in the course of thermal training. It directly leads to pointed and mezhzerenny corrosion and also corrosion energized. The zones enriched with copper differ in the improved properties as galvanic cathode, than an aluminum matrix around, and therefore they are more vulnerable for the corrosion happening on the galvanic mechanism. Increase in content of copper in the mass of alloy increases its strength characteristics due to disperse hardening in the course of aging to 12%. And at copper content in connection over 12% aviation aluminum becomes more fragile.
Aviation aluminum is very demanded metal alloy today. Its high rates of sales first of all are connected with mechanical characteristics among which the defining role is played by ease and durability. These parameters except aircraft industry are very demanded also in production of objects of national consumption, both in shipbuilding, and in the nuclear industry, and in automotive industry, etc. For example, alloys of brands 2014 and 2024 which differ in the moderate content of copper are in special demand. Make the most responsible structural elements of aircraft, military equipment and heavy-load transport of them.
It is necessary to understand that aviation aluminum has important features at connection (welding or soldering) which is carried out only in the environment of inert gases, performing protective function. Helium, argon and their mixes belong to such gases, as a rule. As helium has the highest heat conductivity, it provides the most acceptable indicators of the welding environment. It is very important at connection of structural elements which consist of massive and thick-walled fragments. In this case it is necessary to provide the full gas outlet and to minimize the probability of formation of porous structure of a weld joint.
Application in aircraft industry
As aviation aluminum was initially created for construction of the aircraft equipment, and the sphere of its application first of all is focused on use in production of cases of aircraft, the chassis, the fuel tanks, details of engines, fasteners and other parts of their design.
Aluminum alloys of brand 2HHH are applied to production of details and parts of a design of the aircraft equipment which are affected by the external environment with high temperatures. In turn knots hydraulic, oil and fuel systems are made of alloys of brands 3XXX, 5XXX and 6XXX.
Especially in aircraft industry brand 7075 alloy of which case structural elements (covering and power profiles) and knots which are under the influence of high mechanical loadings, corrosion and low temperatures are made was widely used. In this aluminum alloy copper, magnesium and zinc act as the alloying metals.