Aluminum Welding Services

Aluminium and its Alloys

Aluminium is a chemical element, which makes up about 8% of the Earth’s crust, making it the most abundant metal and the third most abundant element after oxygen and silicon. Aluminium is well known for having a low density (about 2.7 g/cm3) and, through the phenomenon of passivation, excellent corrosion resistance.

As pure aluminium is relatively soft, small amounts of alloying elements are added to produce a range of mechanical properties. The alloys are grouped according to the principal alloying elements. Specific commercial alloys have a four-digit designation according to the international specifications for wrought alloys or the ISO alpha-numeric system. Table 1 provides further details on the make up of these classifications.

The first digit of the series indicates the principal alloying element added to the aluminium alloy and is used to describe the series, i.e. 1000 series or 5000 series, etc. The second digit represents the modification of the specific alloy within the series; i.e. x1xx represents the first modification to the specified alloy, while x2xx represents the second modification. The third and fourth digits identify the alloy within a specific series. To summarise, alloy 2024, is in the 2000 series of alloys, has zero modifications and is specified alloy type 24.

There is, however, an exception to this numbering system and that is for 1000 series aluminium; the last two digits provide the minimum aluminium percentage above 99%. For example, 1050 means 99.50% minimum aluminium content.

Aluminium alloys will also include a temper designation, these define additional processing steps (if implemented). The temper designations are detailed in table 2. Further to the basic temper designations detailed in table 2, there are two sub-designations for ‘H’ – strain hardening, and ‘T’ – thermally treated. Table 3 and 4 describe these ‘H’ and ‘T’ designations, respectively.