Rusts salt water in aluminum

Aluminum alloys for shipbuilding

Pure aluminum is already extremely resistant to corrosion, but it is used relatively rarely in industry. This is often due to the fact that the required end products have to be machined - and pure aluminum is not suitable for this. Therefore, other metals have to be alloyed to both enable machining and maintain corrosion resistance. Aluminum achieves its high corrosion resistance through magnesium as the main alloy additive. Aluminum-magnesium alloys (AlMg) that are used in shipbuilding are, for example:

Aluminum alloys of this type are not only resistant to salt water and the marine atmosphere. Another aspect that comes into play in shipbuilding is the contact between aluminum alloys and other materials. Keyword: contact corrosion. As a rule, aluminum profiles, aluminum wire, plates and sheets as well as aluminum rods and the like are welded, soldered, screwed, riveted or otherwise connected with a wide variety of components and parts made of other materials on board. If aluminum alloys in constructions are in contact with more noble metals such as iron or copper, a so-called contact element can form with the ingress of moisture - an electrochemical reaction.

With water or humidity acting as an electrolytic conductor, the electrons flow from the less noble to the more noble metal, for example at the connection point between an aluminum profile and a copper screw. Within a short period of time, signs of corrosion appear here and several millimeters all around, which make a permanently secure connection impossible.