Metal Glossary

Ageing, Age Hardening, Precipitation Hardening

The second stage in the process (solution treatment and ageing) for those aluminium alloys that respond to heat treatment as a means of increasing their mechanical properties. It entails the precipitation of a constituent from a supersaturated solid solution. The rate of precipitation, and hence ageing, is both temperature and time dependent, with some alloys ageing at room temperature. It is more usual to perform ageing at higher temperatures. It should be noted that routinely operating aged alloys at unusually high ambient temperatures will permit further ageing and even over ageing leading to loss of properties.

Related terms: Aluminium Alloy Classifications


A combination of two or more metals, or of metals and other elements. An alloy is formed by adding the 'alloying elements' to the 'parent' metal in the molten state. The parent metal usually accounts for more than 50% of the resultant mixture.

Alocroming, Alocrom, Chromating

A family of proprietary chemical conversion coating processes based on chromate (hexavalent chromium) solutions that act as a surface pre-treatment before painting or insulation foaming. This also increases the corrosion resistance. More environmentally benign processes based on trivalent chromium are being introduced.

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Aluminium Oxide – A white powder that is produced from the aluminium ore Bauxite and then smelted to produce aluminium metals.

Related terms: Hall Heroult Process

Aluminium Alloy Classifications

Wrought aluminium alloys are specified in British, European and other National standards and are classified in an agreed 4 digit system.
They fall into 2 distinct sub groups:-
1xxx, 3xxx and 5xxx series that develop strength by cold working, the number will be followed by the digit H and other numbers referring to the degree of annealing or cold work, e.g. 3105H22.
2xxx, 6xxx, 7xxx and 8xxx alloys that develop properties by solution treatment and precipitation hardening. The number is usually followed by a T and a number, defining the heat treatment condition of the alloy, e.g. 6082T6.
Thus the 4 digits, the letter and following digits for a product clearly define the chemical composition and the mechanical properties of that material.

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Related terms: Temper Designations

Anodising Quality Material

Material with characteristics that make it suitable for decorative anodising after a suitable preliminary treatment


An electrochemical method for artificially thickening the naturally occurring oxide surface film on Aluminium and Aluminium Alloy surfaces ti improve appearance and/or corrosion resistance. Not all alloy grades are suitable for decorative anodising, with the general rule being the purer the aluminium, the better it will anodise. The thickness and other film characteristics can be controlled to meet varied requirements for improved corrosion resistance, improved abrasion resistance, electrical insulation or as a pre-treatment for subsequently applied coatings. Colour can also be applied using dyes. Anodising film thickness is typically 5 to 25 microns.

Related terms: Anodising Quality Material

Artificial Ageing, Precipitation Treatment

The thermal treatment of an alloy that increases the hardness and strength by precipitation of constituents from the super-saturated solid solution at above room temperature.

Related terms: Age Hardening, Ageing, Precipitation Hardening

As-Quenched Condition

The condition of an alloy during the time immediately following the quench and before the mechanical properties have been significantly raised by precipitation hardening (ageing).