Aluminum alloy

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Aluminum alloys are alloys that mainly consist of aluminum . The most important alloying elements are manganese (Mn), magnesium (Mg), copper (Cu), silicon (Si) and zinc (Zn). In most cases, Al99.5 ( pure aluminum ) with 99.5% aluminum is used as the base material . Alloying can increase strength values ​​within wide limits and also influence other properties.

A distinction is made between hardenable and naturally hard (non-hardenable) alloys, depending on whether the desired increase in strength is achieved only through solid solution strengthening and work hardening or additionally through precipitation hardening (special heat treatment ).

  • The naturally hard alloys are of the type AlMn , AlMg , AlMgMn and AlSi .
  • The hardenable alloys are AlCuMg , AlCuSiMn, AlMgSi , AlZnMg and AlZnMgCu. They are processed into semi-finished products in the form of strips, sheets and blanks, tubes, rods and wires, extruded profiles and forgings.

Another distinction arises from the type of processing: wrought or cast materials . All types are used as wrought alloys, with AlSi almost never being used as wrought alloys. The cast materials include the alloys AlSi (including AlSiMg, AlSiCu) because of their good castability as well as AlMg, AlMgSi, AlCuTi, AlCuTiMg.

Alloy elements

Numerous alloying elements occur in aluminum alloys . The main alloying elements used are silicon , magnesium , manganese , copper and zinc . They increase the strength through what is known as solid solution strengthening . With pure aluminum, the atoms are arranged in a regular structure. In the alloys, some of the aluminum atoms have been replaced by atoms of the other elements. Since these have a size that differs from that of the aluminum atoms, the atoms are more difficult to move relative to one another, which is noticeable as a higher strength. Some also form precipitates (areas that are poor or free of aluminum) which also increase strength. Zinc (together with magnesium) and copper are used for high strength. For medium strengths manganese, magnesium and silicon. The latter also improves castability .

Accompanying elements are iron and silicon that come from the electrolysis process in the production of aluminum. Most of the time these are contaminants that are undesirable. Iron in particular has a negative effect on strength, as it forms various intermetallic phases . It is used to bind silicon, which improves the electrical conductivity and to reduce the tendency to stick in alloys that are intended for die casting . Otherwise these tend to stick to the permanent steel molds .

There are also special alloy elements. Titanium , boron , manganese, zirconium , chromium , vanadium and scandium are used for grain refinement . Even very small amounts thereof are used as so-called nucleation during solidification of the melt , so that it solidifies at the same time at many points, which a finer structure and higher strength has resulted. Bismuth , lead and sulfur are used to improve the breaking of the chips during milling, drilling and turning. The effect corresponds to that of these elements in free-cutting steel . The elements lithium and scandium are much lighter than aluminum and serve to reduce the density, which is particularly advantageous for alloys for aerospace applications.

Wrought aluminum alloys

Wrought aluminum alloys are all aluminum alloys that are mainly processed by forming (rolling, extrusion) ( wrought alloys ).

Even small amounts of the alloying elements magnesium, silicon, copper, zinc, nickel and manganese change the properties of pure aluminum very strongly. These find z. B. in engine and transmission construction, pipe construction and mechanical engineering use, as they result in a wear-resistant connection. In particular, strength and hardness are increased, electrical conductivity is reduced, while deformability only decreases slightly. These alloys show high ductility , which is why they are called wrought aluminum alloys. Due to their high strength and low density, wrought aluminum alloys are used as materials for transport containers and structural parts in vehicle, aircraft and shipbuilding.

Wrought aluminum alloys are usually designated with a four-digit number system created by the Aluminum Association instead of their material number. The first digit indicates the main alloy element and thus the alloy group. The remaining digits are more or less numerical numbers that are assigned chronologically or based on existing alloys.

Overview of the designation system for wrought aluminum alloys according to EN 573-3 / 4
group Main
Hardenability Strength
[N / mm²]
1xxx at least 99% aluminum not hardenable 070… 190
(see aluminum-
copper alloy
copper curable 190… 570
  • high strength, susceptible to corrosion, mostly difficult or impossible to weld
  • Use in aircraft construction and space travel
  • Welding filler mostly 2xxx, sometimes 4xxx
(see aluminum-
manganese alloy
manganese not hardenable 100 ... 350
  • low strength, high corrosion resistance, good formability, also suitable for higher temperatures
  • Field of application from saucepans to coolers in vehicles (often clad with 4xxx here) to power plant construction
  • Welding consumables 1xxx, 4xxx and 5xxx
(see aluminum-
silicon alloy
Silicon age-hardenable and
170 ... 380
  • only series containing hardenable and non-hardenable alloys
  • the presence of magnesium is also required for hardening . Silicon reduces the melting point and makes the melt more fluid
  • ideal for welding and soldering additives
(see aluminum-
magnesium alloy
Magnesium (without silicon) not hardenable 100 ... 450
  • medium to high strengths, weldable
  • Use in shipbuilding, transport, pressure vessels, bridges and buildings, as AA5024 (AlMgSc) also for use in aviation. Welding filler must be determined according to the magnesium content. Aluminum from this series with more than 3.0% Mg is not suitable for temperatures above 65 ° C ( stress corrosion cracking )
  • Materials with less than approx. 2.5% Mg can often be successfully welded with 5xxx or 4xxx consumables. 5032 is usually mentioned as the material with the highest Mg content, which can just be welded with 4xxx
6xxx (see aluminum-magnesium-silicon alloy ) Magnesium
curable 100 ... 450
  • Si and Mg around 1%, very easy to weld and extrude
  • Mainly used as extruded profiles
  • should not be welded without welding consumables (hot cracks)
  • 4xxx and 5xxx welding consumables
7xxx zinc curable 220 ... 700
  • 0.8 to 12.0% Zn, high to very high strength
  • Used in aircraft construction, aerospace, sports equipment, cell phone housings and watches
  • some alloys cannot be arc welded
  • Alloys 7005 (trade name Ergal ) and 7020 can be welded well with 5xxx welding consumables, since these two alloys do not contain any copper
8xxx other
differently differently
List of typical aluminum alloys that are used in industry (figures in percent)
Surname Silicon manganese magnesium copper
Aludur 0.3-1 0.3-0.8 0.5-1.2 -
Aluman - 1.1 - -
Duralumin 0.2-1.0 0.5-1.2 0.2-5 2.5-5.5
Hydronalium 0.2-1.0 0.2-0.8 3-12 -
Silumin until 14 - - -

Cast aluminum alloys

See also: Aluminum casting - casting of aluminum materials.

The following classification applies to cast alloys :

  • 1xxxx: pure aluminum qualities
  • 2xxxx: copper ( AlCu )
  • 3xxxx: silicon-copper / magnesium (see under AlSi )
  • 4xxxx: silicon ( AlSi )
  • 5xxxx: Magnesium ( AlMg )
  • 7xxxx: zinc
  • 8xxxx: tin
  • 9xxxx: master alloys

The most important type of cast aluminum is the eutectic alloy of aluminum and silicon. Their eutectic is around 12% silicon and has a melting point of 576 ° C. This aluminum-silicon alloy has excellent casting properties (thin liquid, low shrinkage ) and is very strong . It is generally easy to weld and corrosion resistant. Magnesium and copper add to strength, but copper reduces corrosion resistance.

Cast aluminum alloys with these elements are used as materials, for example for engine housings and transmission housings in vehicle and aircraft construction.

Since aluminum melt to oxide - and tends to foam, the need casting method are the effect adapted and developed. Is becoming increasingly important in the chill casting the tiltabe casting .

Web links

Wiktionary: aluminum alloy  - explanations of meanings, word origins, synonyms, translations


Individual evidence

  1. ^ Friedrich Ostermann: Application technology aluminum. Springer-Verlag, Berlin Heidelberg 2014, 3rd edition, pp. 86–87.
  2. ^ Rüdiger Bähr : Urformen . In: Karl-Heinrich Grote , Jörg Feldhusen (Hrsg.): Dubbel - pocket book for mechanical engineering . 24th edition. Springer , Berlin / Heidelberg 2014, ISBN 978-3-642-38890-3 , pp. 1347-1371 .
  3. Günter Spur : Handbook Urformen . 2nd Edition. Carl Hanser Verlag , 2013, p. 283-286 .