Aluminum alloy
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 In the alloys, some of the aluminum atoms have been replaced by atoms of the other elements.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.
group | Main alloy element |
Hardenability | Strength [N / mm²] |
Remarks |
---|---|---|---|---|
1xxx | at least 99% aluminum | not hardenable | 70… 190 |
|
2xxx (see aluminum- copper alloy ) |
copper | curable | 190… 570 |
|
3xxx (see aluminum- manganese alloy ) |
manganese | not hardenable | 100 ... 350 |
|
4xxx (see aluminum- silicon alloy ) |
Silicon | age-hardenable and non-age-hardenable alloys |
170 ... 380 |
|
5xxx (see aluminum- magnesium alloy ) |
Magnesium (without silicon) | not hardenable | 100 ... 450 |
|
6xxx (see aluminum-magnesium-silicon alloy ) | Magnesium and silicon |
curable | 100 ... 450 |
|
7xxx | zinc | curable | 220 ... 700 |
|
8xxx | other elements |
differently | differently |
|
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
- Aluminum Lexicon - the material from A – Z. Alloy elements. In: aluinfo.de. General Association of the Aluminum Industry, accessed on May 11, 2020 .
literature
- Friedrich Ostermann: Application technology aluminum. Springer-Verlag, Berlin Heidelberg 2014, ISBN 978-3-662-43806-0 .
- Catrin Kammer: Aluminum paperback. Beuth Verlag, Berlin 2011, ISBN 978-3-410-22028-2 .
Individual evidence
- ^ Friedrich Ostermann: Application technology aluminum. Springer-Verlag, Berlin Heidelberg 2014, 3rd edition, pp. 86–87.
- ^ 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 .
- ↑ Günter Spur : Handbook Urformen . 2nd Edition. Carl Hanser Verlag , 2013, p. 283-286 .