Aluminum-manganese alloy
Aluminum-manganese alloys ( AlMn alloys ) are aluminum alloys that contain manganese (Mn) as the main alloying element . They consist mainly of aluminum (Al); In addition to manganese, which has the largest share of the alloy elements with around 1%, iron (Fe), silicon (Si), magnesium (Mg) or copper (Cu) can also be included. AlMn is used almost exclusively as a wrought alloy and processed into sheets or profiles by rolling or extrusion . The alloys are corrosion-resistant , have low strengths for aluminum alloys and can not be hardened (through heat treatment ) . They are standardized in the 3000 series.
Applications
Aluminum-manganese alloys are used for applications with low requirements on strength and, due to their corrosion resistance, can also be used in chemical and food-related environments. AlMn is therefore not a construction material , but a functional material .
AlMn is processed into beverage cans and generally used as packaging material. It is used for apparatus and pipes in the chemical industry , for roof tiles, wall coverings , pressure vessel , roller shutters , rolling gates and for heat exchanger .
Influences of the alloying elements
Manganese combines with aluminum to form intermetallic phases and thus increases strength. Every percent of manganese increases strength by about 42 MPa. Iron and silicon are mostly undesirable accompanying elements that cannot be completely removed. Magnesium and copper increase the strength better (70–85 MPa per% Mg) and are added to the alloy to increase strength.
Phases
Binary aluminum-manganese phases
Aluminum and manganese are partially miscible in the solid state. They also form different intermetallic phases .
The eutectic between aluminum and Al 6 Mn is 1.3% Mn and 660 ° C, while pure aluminum melts at 660.2 ° C. In older literature values of 1.8% and 657 ° C or 658 ° C can also be found.
Above 710 ° C, Al 4 Mn is formed with Mn contents of at least 4%. However, such high levels are not used technically. Below 510 ° C or 511 ° C, Al 12 Mn forms.
The solubility of manganese in the aluminum mixed crystal drops rapidly as the temperature drops and is close to zero at room temperature.
Phases in AlMn materials with other elements
Some of the AlMn materials still contain iron (Fe) or silicon (Si) additives. These form the phases Al 3 Fe, Al 8 Fe 2 Si, Al 5 FeSi, Al 15 Si 2 (Mn, Fe) 3 . In addition, mixed crystals occur in the form of Al 12 (Mn, Fe) 3 Si.
- From the melt, Al 3 Fe and Al 6 (Mn, Fe), aluminum and Al 15 Si 2 (Mn, Fe) 3 are formed at 648 ° C
- From the melt, Al 3 Fe, aluminum, Al 15 Si 2 (Mn, Fe) 3 and Al 8 Fe 2 Si are formed at below 630 ° C
- From the melt and Al 8 Fe 2 Si, aluminum, Al 5 FeSi and Al 15 Si 2 (Mn, Fe) 3 are formed at around 600 ° C
- From the melt and Al 5 FeSi, aluminum, silicon and Al 15 Si 2 (Mn, Fe) 3 are formed at around 565 ° C
structure
The structure after casting into bars or slabs consists mainly of a supersaturated solid solution and precipitated areas with phases containing manganese, the size of which is around 100 µm. A large part of the manganese (about 0.7 to 0.9%) is still dissolved in the aluminum, since the cooling rates after casting are too great for all of the manganese to be separated out by diffusion . The reason for this is also the very low diffusion speed of manganese in aluminum.
The structure changes through homogenization and reshaping (rolling, forging). Different phases are separated from the basic aluminum structure, the size of which is less than one micrometer. These particles increase the strength compared to pure aluminum by about 25%. They are thermally stable and can only be dissolved again with difficulty. In the reshaped and homogenized state, there is a very fine structure, the larger, manganese-containing areas from the as-cast state are no longer present. These finely divided particles also hinder grain growth and thus improve the strength of the material; however, this improvement is only slight, since in the case of aluminum materials it is generally only slightly dependent on the grain size.
The presence of silicon accelerates the precipitation of Al 12 (Mn, Fe) 3 Si. If there is enough silicon, the Al 6 (Mn, Fe) is transformed into Al 12 (Mn, Fe) 3 Si during the homogenization .
Properties and standardized alloys
| together setting |
code | Status |
Elastic limit |
Tensile strength |
fracture strain |
|---|---|---|---|---|---|
| AlMn1Cu | 3003 | O ( annealed ) HX2 ( work hardened 1/4-hard) |
50 MPa 120 MPa |
110 MPa 140 MPa |
29% 11%
|
| AlMn1 | 3103 | O HX2 |
45 MPa 115 MPa |
105 MPa 135 MPa |
29% 11%
|
literature
- Friedrich Ostermann: Application technology aluminum. 3. Edition. Springer, 2014, ISBN 978-3-662-43806-0 , pp. 100-102.
- Aluminum paperback. Volume 1: Fundamentals and materials. 16th edition. Beuth-Verlag, Berlin / Vienna / Zurich 2002, ISBN 3-87017-274-6 , pp. 104 f, 122.
- George E. Totten, D. Scott MacKenzie: Handbook of Aluminum. Volume 1: Physical Metallurgy and Processes . Marcel Dekker, New York / Basel 2003, ISBN 0-8247-0494-0 , pp. 159f.