This corrosion takes place when two different metals have contact with each other in the prescence of an electrolyte. The less noble metal (anode) of the combination corrodes while the noble (cathode) will be protected. A small surface of the cathode and a large surface of the anode lead to a low corrosion. In reverse case the Aluminium will be attacked quickly. In most combinations with other metals, Aluminium is the less noble.