Aluminium–manganese alloys (AlMn alloys) are

aluminium alloys An aluminium alloy (or aluminum alloy; see spelling differences) is an alloy in which aluminium (Al) is the predominant metal. The typical alloying elements are copper, magnesium, manganese, silicon, tin, nickel and zinc. There are two principal ...

that contain

manganese Manganese is a chemical element with the symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of industrial alloy use ...

(Mn) as the main alloying element. They consist mainly of

aluminium Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. I ...

(Al); in addition to manganese, which accounts for the largest proportion of about 1% of the alloying elements, but they may also contain small amounts of

iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...

(Fe),

silicon Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic tab ...

(Si),

magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...

(Mg), or

copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...

(Cu). AlMn is almost only used as a

wrought alloy Wrought is the archaic form of "worked," the more commonly used past tense and past participle of work. Wrought may also refer to: * Metalworking, the process of working with metals to create individual parts, assemblies, or large-scale structure ...

and is processed into sheets or profiles by

rolling Rolling is a type of motion that combines rotation (commonly, of an axially symmetric object) and translation of that object with respect to a surface (either one or the other moves), such that, if ideal conditions exist, the two are in contact ...

extrusion Extrusion is a process used to create objects of a fixed cross-sectional profile by pushing material through a die of the desired cross-section. Its two main advantages over other manufacturing processes are its ability to create very complex c ...

presses. These alloys are

corrosion-resistant Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engine ...

, have low strengths for aluminium alloys, and are not hardenable (by heat treatment). They are standard in the 3000 series.

Applications

Aluminium–manganese alloys are used in applications with low strength requirements and also in chemical and food-related environments due to their corrosion resistance. AlMn is therefore used more commonly as a functional material than a construction material. AlMn is processed into beverage cans and is generally referred to as the

packaging material Packaging is the science, art and technology of enclosing or protecting products for distribution, storage, sale, and use. Packaging also refers to the process of designing, evaluating, and producing packages. Packaging can be described as a co ...

used. It is used for apparatus and pipes in the

chemical industry The chemical industry comprises the companies that produce industrial chemicals. Central to the modern world economy, it converts raw materials (oil, natural gas, air, water, metals, and minerals) into more than 70,000 different products. The ...

, for roof

cladding Cladding is an outer layer of material covering another. It may refer to the following: *Cladding (boiler), the layer of insulation and outer wrapping around a boiler shell *Cladding (construction), materials applied to the exterior of buildings ...

, wall coverings,

pressure vessel A pressure vessel is a container designed to hold gases or liquids at a pressure substantially different from the ambient pressure. Construction methods and materials may be chosen to suit the pressure application, and will depend on the size o ...

roller shutter A roller shutter, security shutter, coiling door, roller door or sectional overhead door is a type of door or window shutter consisting of many horizontal slats (or sometimes bars or web systems) hinged together. The door is raised to open it ...

s, roller doors, and

heat exchanger A heat exchanger is a system used to transfer heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct contac ...

Influences of the alloy elements

Manganese combines with aluminium to form intermetallic phases—phases which contain a different crystallographic structure than either manganese or alumunium by itself. Compared to conventional alloys, the increased metallic bonding within the intermetallic phase of AlMn increases its strength and chemical resistance. Each percent of manganese increases its strength by about 42 MPa. Iron and silicon are usually unwanted accompanying elements that cannot be completely removed. Magnesium and copper are more effective in enhancing strength, providing an increase of 70–85 MPa per % of Mg when added to the alloy.

Phases

Binary aluminium manganese phases

Aluminium and manganese are partially miscible in the solid state, meaning they can mix to some extent in the solid phase. However, their complete solubility in each other is limited, and they tend to form various intermetallic phases. The eutectic, between aluminium and Al₆Mn is 1.3% manganese and 660 °C, while pure aluminium melts at 660.2 °C. Values of 1.8% and 657 °C or 658 °C can also be found in older literature. Above 710 °C, Al₄Mn is formed with a manganese content of at least 4%. However, such high levels are not typically used. Below 510 or 511 °C, Al₁₂Mn forms. The solubility of manganese in the Mn-Al

solid solution A solid solution, a term popularly used for metals, is a homogenous mixture of two different kinds of atoms in solid state and have a single crystal structure. Many examples can be found in metallurgy, geology, and solid-state chemistry. The word ...

falls rapidly with decreasing temperature and is close to zero at room temperature.

Phases in AlMn materials with other elements

Some of the AlMn materials also contain iron (Fe) or silicon (Si) additives. These form the phases Al₃Fe, Al₈Fe₂Si, Al₅FeSi, Al₁₅Si₂(Mn,Fe)₃. Mixed crystals also occur in the form of Al₁₂(Mn, Fe)₃Si. * Aluminium and Al₁₅Si₂(Mn,Fe)₃ are formed from the melt, Al₃Fe and Al₆(Mn,Fe) at 648 °C. * At temperatures below 630 °C, aluminium, Al₁₅Si₂(Mn,Fe)₃ and Al₈Fe₂Si are formed from the melt, Al₃Fe. * Aluminium, Al₅FeSi and Al₁₅Si₂(Mn,Fe)₃ are formed from the melt and Al₈Fe₂Si at around 600 °C. * Aluminium, silicon and Al₁₅Si₂(Mn,Fe)₃ are formed from the melt and Al₅FeSi at around 565 °C.

Structures

The structure resulting from casting into bars or slabs consists of the main mass, which is an oversaturated mixed crystal, along with areas containing manganese-containing phases that have an average size of about 100 μm. A significant portion of the manganese (approximately 0.7 to 0.9%) remains dissolved in aluminium because the cooling rates after casting are too rapid for all the manganese to undergo diffusion and precipitate. This is further exacerbated by the very low diffusion speed of manganese in aluminium. Through processes such as

homogenization Homogeneity is a sameness of constituent structure. Homogeneity, homogeneous, or homogenization may also refer to: In mathematics *Transcendental law of homogeneity of Leibniz * Homogeneous space for a Lie group G, or more general transformati ...

and forming (rolling, forging), the structure of the material undergoes changes. During this transformation, various phases that were previously present within the basic aluminium crystal structure, each having a size of less than one micron, are eliminated. These particles contribute to an approximately 25% increase in strength compared to pure aluminium. They exhibit thermal stability and are challenging to dissolve. In the formed and homogenized state, the material exhibits a very fine structure, and the larger manganese-containing areas observed in the initial casting state are no longer present. These finely dispersed particles also impede

grain growth In materials science, grain growth is the increase in size of grains (crystallites) in a material at high temperature. This occurs when recovery and recrystallisation are complete and further reduction in the internal energy can only be achieved ...

, further enhancing the material's strength. However, it's important to note that this improvement is relatively modest, as the influence of grain size on the strength of aluminium materials is generally limited. The presence of silicon accelerates the excretion of Al₁₂(Mn, Fe)₃Si.Totten, MacKenzie, S. 160. If there is enough silicon, the Al₆(Mn,Fe) is converted to Al₁₂(Mn,Fe)₃Si during homogenization.

Properties and standardised alloys

3000 series

3000 series are alloyed with

and can be

work hardened In materials science, work hardening, also known as strain hardening, is the strengthening of a metal or polymer by plastic deformation. Work hardening may be desirable, undesirable, or inconsequential, depending on the context. This strengt ...