In the anodic branch of the diagram, the corrosion current increases abruptly due to the presence of a top layer on the alloy surface. In contact with the corrosive environment, some active metals suddenly become incredibly resistant to corrosion. This is due to a phenomenon called chemical passivation. In these situations, the metal goes through a reaction and creates a layer of very thin corrosion products that is invisible and is a complete barrier that reduces corrosion by several orders of magnitude . In the case of Aluminum and its alloys, a sticky oxide layer is slowly formed when the alloy is exposed to the air. This adhesive oxide layer on the surface causes corrosion resistance in Aluminum alloys. Considering all four samples, the corrosion resistance can be expressed as follow: