Pure aluminium is soft and not very strong. It is therefore alloyed with other elements, magnesium, silicon, copper, zinc or manganese, to obtain markedly stronger materials that keep its lightness (around 2.7 g/cm³, about a third of the mass of steel), its good thermal conductivity and its ease of machining. In Europe, wrought alloys, that is, rolled, extruded or forged, are designated by EN AW followed by four digits (for example EN AW-6082), and casting alloys by EN AC. To estimate what your part will weigh, see the part mass calculation tool.
The first digit indicates the family: 1000 (almost pure aluminium), 2000 (copper), 3000 (manganese), 4000 (silicon), 5000 (magnesium), 6000 (magnesium and silicon), 7000 (zinc). The 6000 series, versatile, weldable and anodisable, are the most used in mechanical engineering (6082, 6061). The 5000 series, such as 5083, resist marine corrosion well and can be welded; the 7000 series, such as 7075, offer the highest strength but cannot be welded. The 2000 series, such as 2017A, machine very well but are less well protected against corrosion.
The designation ends with a temper: T6 or T651 for precipitation-hardening alloys (solution treatment, quenching, ageing), H for work-hardened alloys such as the 5000 series. This temper sets the hardness and the machining behaviour, hence the value of specifying it. These alloys can be anodised, with a result that varies by alloy, machined quickly and, for the most part, TIG welded.
In a quote request
Write the full designation (EN AW-6082 T6, for example) rather than “alu”, say whether an equivalent grade is accepted, the form of the stock (bar, plate) and the material certificate expected. Flag whether the part will be welded or anodised, as this guides the choice of alloy. See the guides aluminium 5083, 6061 and 7075 and materials for machined parts, as well as the definition of stainless steel for comparison.