Influence of main elements, Mg and Si (Topic 11008)

Magnesium (Mg) improves the corrosion properties, especially in alkaline environments.

Silicon (Si) has a slightly negative effect on corrosion properties, but this is very dependent on the distribution of Si in the microstructure.

In a balanced alloy in the 6000-group, the relation Mg/Si is 1,73, this corresponds to the stoichiometric distribution in Mg2Si and assumes that all Mg and Si are present as Mg2Si phase.

The Si and Mg content for some of the more common alloys used for commercial extrusion are shown below. In the same figure the results from an accelerated corrosion test are included [56].

Si and Mg content for common alloys used for extrusion billet. For Si levels below 0,6ñ0,9%, pitting corrosion dominates, susceptibility to intergranular corrosion increases with increasing Si content and above 0,6ñ0,9% this corrosion type dominates. The sensitivity to stress corrosion cracking and exfoliation may also increase when the susceptibility to intergranular corrosion increases, but this is not always the case. Read this ,