The most common types of aluminium corrosion are galvanic corrosion and pitting. If your material is corroding, you have probably encountered one of the two.
1.Galvanic corrosion
Galvanic corrosion occurs when two metals degrade each other. If aluminium comes into contact with a more noble metal (e.g. copper, zinc and certain types of steel) through an electrolyte (e.g. salt water), the aluminium will degrade.
The electrolyte is necessary for galvanic corrosion to happen. This makes marine environments the main risk factor, and you should take precautions in these areas.
In a dry indoor environment or a non-marine outdoor environment, combining aluminium with a more noble metal is generally not a problem.
Prevention of galvanic corrosion
There are various methods to prevent galvanic corrosion. One simple method is to insulate the different metals with electrical insulation. This breaks the electrical contact created by the electrolyte.
You can also use a surface treatment, e.g. paint, on the most noble metal to protect against galvanic corrosion. Make sure that the coating is tightly sealed - even small scratches can be enough to ignite the corrosion reaction. Read more about surface treatment as a protective measure here.
Another method is to use sacrificial anodes. This involves "sacrificing" another metal that is less noble than aluminium. The metal is placed on the aluminium, which is now no longer the less noble metal, and the corrosion will attack the sacrificial anode.
Mechanical surface treatment can be a source of galvanic corrosion if you are not careful. It is very important that the tools do not contain copper or steel, which can react with aluminium.
It is also important that the tools are not used on other metals. If the tool transfers particles or chips from other metals to the aluminium surface, there is a high risk of galvanic corrosion. For the same reason, make sure to keep a physical distance from aluminium parts when treating or machining other metals so chips from the other metal does not land on the aluminium.
2.Pitting
Pitting is less severe than galvanic corrosion. Pitting is usually a local issue that is primarily aesthetic.
Like galvanic corrosion, pitting is caused by an electrolyte - i.e. salty water or moisture.
Aluminium in humid, salty environments is at risk of pitting. Dirt on the aluminium surface can also be a risk factor if it traps moisture on the surface and creates a breeding ground for pitting.
Prevention of pitting
Pitting is usually superficial and does not affect the strength of the material. However, to prevent pitting, it's important to keep the aluminium surface dry and reasonably clean.
We recommend rinsing the surface with water regularly (1-2 times a year) and designing the surface in a way that leads water and moisture away.
A simple surface treatment such as anodising or painting also offers good protection against pitting.
Filiform corrosion
With painted items there is a risk of filiform corrosion. Filiform corrosion occurs when liquids get under the paint and react with the exposed aluminium surface.
