The nomenclature of Aluminum Alloys

Before going into the influence of the alloying elements on the Anodizing result I would like to talk about the designation of aluminum alloys.

Pure aluminum is a very soft and ductile material. Alloying with various elements are therefore necessary to improve the mechanical properties of the aluminum material. The total amount of alloying elements is usually less than 15 wt%.

To be able to buy the same alloy for production every time, a system for specifying commercial alloys is necessary.

The first official designation of an alloy was established in 1888, designating a commercially pure aluminum alloy. Lots of other alloy designation systems have been used over the years but today the European nomenclature (EN) and the Aluminum Association (AA) which is almost identically is more or less followed.

For wrought alloys the description is by four digits followed by letter and number indicating the temper or condition of alloy.

1xxx Aluminum of 99% minimum purity
2xxx Aluminum – copper alloys
3xxx Aluminum – manganese alloys
4xxx Aluminum – silicium alloys
5xxx Aluminum – magnesium
6xxx Aluminum – magnesium – silicium alloys
7xxx Aluminum – zinc – magnesium alloys
8xxx Aluminum – lithium and other alloys

These alloys can be divided into two groups, the heat treatable and work hardening (non-heat treatable) alloys. The heat treatable alloys are the ones containing one or more of the elements copper, magnesium, silicon and zinc. These alloying elements are soluble in aluminum to a considerable amount at elevated temperatures. These alloys are generally found in the 2xxx, 6xxx and 7xxx series with few exceptions in the 4xxx and 5xxx series.

For the work hardening alloys the strength is developed by solid solution hardening and by strain hardening from the annealed temper. The main alloys in this group are 1xxx, 3xxx, 4xxx and 5xxx. Few work hardening alloys occur in the 7xxx and 8xxx series.

Turning to the casting (foundry) alloys the designation of these is not as standardised as for the wrought alloys. One of the most widely used is the three digits system standardised by Aluminum Association (AA).

1xx Aluminum of 99% minimum purity
2xx Aluminum – copper
3xx Aluminum – silicium – magnesium, Aluminum – silicium – copper, Aluminum – silicium – copper – magnesium
4xx Aluminum – silicium
5xx Aluminum – magnesium
7xx Aluminum – zinc
8xx Aluminum – tin

The most reliable way to designate alloys is the one using letters and numbers, as for example AlSi7Mg0.3. This designation tells what main alloying elements are present. In the alloy 7 wt% silicon and 0.3 wt% magnesium is added, the rest of the alloying elements amount to less than 1 wt%.

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