Glossary

Interesting facts about aluminum: Read short and concise information about the alloys and processing of aluminum. Alongside steel, aluminum is the most commonly used metal.

As specialists in the trade and processing of aluminum, steel and some heavy metals, we offer a wide range of services: Find out more about our metal trade with a broad product range and metal processing with a view to the functionality and application of individual parts and assemblies.

Aluminum glossary

Aluminum
Aluminum is the most common metal. It is silvery white, light and corrosion-resistant. Aluminum was only discovered in the 19th century and is now the most important metal in everyday use alongside steel and is also a better electrical conductor than copper in terms of weight.
Anodic oxidation
A process for strengthening the protective oxide layer of aluminium (also known as anodizing): The workpiece to be treated is placed in an electrically conductive liquid (electrolyte) where it is connected to a DC voltage source as an anode. In the resulting voltage field, anions containing oxygen migrate to the aluminum surface. There they react with the material, forming aluminum oxide. Hydrogen is formed at the cathode and escapes in the form of gas. The resulting oxide layer consists of an extremely thin so-called barrier layer, which is almost non-porous, extremely dense and electrically insulating, and a much thicker, slightly porous and electrically conductive top layer, which is formed by a chemical reaction between the barrier layer and the electrolyte.
Age-hardenable alloy
Age-hardenable alloys are alloys whose strength can be increased by heat treatment.
Hardening
Hardening is an effective method of increasing strength, which is only possible with hardenable alloys: Through solution annealing, quenching and ageing,
alloy components are separated out in the form of very finely distributed particles, which block displacement surfaces and thus hinder dislocation movements in the aluminum structure.
Ageing
If aluminum alloys are stored at room temperature (cold ageing) or at a slightly elevated temperature (artificial ageing) for a longer period of time, the foreign atoms of the alloy components precipitate out of the solid solution, forming particles. Due to the critical size and/or the phase boundary, this increases the strength. Ageing is
generally the final stage of heat treatment.
Coil coating
Coil coating is a process in which liquid or powder coatings are continuously applied to aluminum strips in a system. The coils are first pre-treated in the system, i.e. degreased, pickled and chromated or phosphated, after which the paint is applied in the coating station, e.g. by rolling, and then baked. This process is characterized by a highly efficient working method, in which large quantities of aluminium strips can be provided with the same coating. The careful matching of material and lacquer also means that coil-coated aluminum can be further formed after the sheet metal working process without the coating tearing or cracking.
Direct extrusion process
Direct extrusion is the simplest variant of extrusion: A billet (block) heated to around 450 – 500°C is inserted into the recipient and pressed through a shaping die using a hydraulically operated press ram. The block and die remain stationary.
Modulus of elasticity
The modulus of elasticity (also known as Young’s modulus) is a measurement that indicates how much a material stretches elastically under a given load.
Electrical conductivity
Electrical conductivity is a measure of the ability of substances to conduct electricity. Whether and how strongly a given substance conducts electricity depends on the number and mobility of the free charge carriers. This leads to the classification into three electrical substance classes: Conductors, semiconductors and non-conductors.
Strength
The amount of resistance to a load up to breakage is called strength. It is low for most metals, but can be increased by alloying, forming or
heat treatment. The unit of measurement for strength is N/mm2.
Casting structure / casting grain
During the solidification of a metal, so-called crystallization nuclei form in many places in the melt. They grow constantly during the solidification process at
and form the casting grains. When these finally collide, the growth stops. The size and shape of the casting grains is determined by the solidification conditions and the composition of the molten metal. The entirety of the cast grains is referred to as the cast structure.
Homogenization annealing
Homogenization annealing is a heat treatment process that compensates for local depletions or accumulations of foreign atoms in the microstructure (caused by segregation). For this purpose, the workpiece in question is annealed close to the solidus temperature so that the inhomogeneities are balanced out by diffusion processes.
Cold aging
Storage at room temperature causes the formation of coherent precipitates in the structure, also known as Guinier-Preston zones. In this state, the lattice connections are “distorted”. If you want to shift this coherence stress field, this is only possible with additional energy input. The Guinier-Preston zones therefore lead to a significant increase in hardness, tensile strength and the 0.2% yield strength.

Wrought alloys
There are two forms of aluminum alloys: Cast alloys and wrought alloys. Wrought alloys are characterized by the fact that they contain up to 10% alloying elements and are intended for forming. The focus here is on plastic deformability.
Solution annealing
Solution annealing is usually carried out as part of the hardening process. At a temperature of approx. 460 – 560 °C, the alloying elements that are unevenly distributed in the microstructure are dissolved and homogenized in the solid solution.
Naturally hard alloy
Naturally hard (non-hardenable) alloys are alloys whose strength can no longer be increased by heat treatment. The alloying elements contained are already completely dissolved.
Oxide layer
The oxide layer is a very thin “skin” of aluminum oxides that spontaneously coats aluminum materials in air and water and protects the metal underneath from corrosion.
Primary aluminum
Primary aluminum is “new” aluminum obtained from alumina as opposed to recycled, remelted aluminum (secondary aluminum). Primary aluminum accounts for around 70% of global production. It is used where particularly high demands are placed on the metal.
Stretching
If necessary, stretching follows rolling and extrusion and is carried out after the product has cooled down. It serves to improve the structure and flatness. Stretching is a manual and therefore costly process. The product is stretched by 2% at both ends and then straightened.
Secondary aluminum
Secondary aluminum is aluminum recovered from old or new scrap as part of the recycling process. It accounts for around 30% of global aluminum production. It is mainly used in the form of casting alloys. The energy required to remelt scrap into secondary aluminum is up to 95% less than that required to extract primary aluminum.
Machinability
The term machinability refers to the ability of a material to be machined using the forming process. Compared to other metallic materials, aluminum is considered easy to machine.
Stress
Stress is a load exerted on the cross-section of a material. Depending on its direction, it is referred to as compressive or tensile stress, for example.
Extrusion
Extrusion is the production of profiles in an extrusion press. In this forming process, a billet is pressed through a shaping tool (a so-called die) while retaining its mass and is plastically deformed accordingly. The die determines the cross-section of the emerging profile.
Rolling slabs
Rolling slabs are the starting material for the manufacture of rolled products. These are rectangular, cast ingots with dimensions of between 200 and 600 mm thickness, between 600 and 2200 mm width and up to 8000 mm length. They weigh between 1.5 and 30 tons.
Rolling
During rolling, aluminum ingots and strips are rolled into strips, sheets and foils. A distinction is made between hot rolling (with large ingots preheated to 500 to 600 °C as starting material) and cold rolling (at 350 to 400 °C).
Artificial ageing
Ageing in general usually marks the end of a heat treatment process. Artificial ageing in particular means ageing at temperatures of around 100 to 200 °C, which results in a series of metastable phases accompanied by hardening effects. The increase in strength is somewhat lower than with cold ageing.
Tensile strength
The tensile strength is the most important key figure when specifying the strength of a material. It is a measure of the force that the respective material can just about withstand as the highest tensile stress before it breaks. The tensile strength is measured in a tearing machine on rods of the material in question.
0.2% proof stress
The 0.2% proof stress is a measure of the strength of an aluminum material. It is the force that must be applied as tensile stress to cause a permanent elongation of the material of 0.2%. The measure is N/mm2.