aluminium in commercial vehicles - European Aluminium Association

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146 EUROPEAN ALUMINIUM ASSOCIATION ALUMINIUM IN COMMERCIAL VEHICLES CHAPTER XI 1. Definition of corrosion Corrosion is a electrochemical interaction between a metal and its environment which results in changes in the properties of the metal and which may often lead to impairment of the function of the metal, the environment, or the technical system of which these form a part (definition as per EN ISO 8044). 2. Corrosion of aluminium 2.1. The natural oxide layer A clean aluminium surface is very reactive and will react sponta- neously with air or water to form aluminium oxide. This oxide builds a natural protective layer on each aluminium surface with a thickness of around 1 – 10 nm. The oxide layer is chemically very stable, has a good adhesion to the metal surface, repairs itself and protects the aluminium from further corrosion. (Figure XI.1) The oxide layer can be destroyed in strong acidic or alkaline environments or where aggressive ions are present. Aggressive ions can destroy the layer locally and lead to local corrosion attack (“pitting”). A typical case for this reaction is the contact between aluminium and chloride ions, which are present in seawater or road salts. Some alloying elements might increase the corrosion resistance of the oxide layer, while others can weaken it. FIGURE XI.1 Natural oxide layer (Al O ) 2 3 Aluminium substrate Corrosion can occur locally (“pitting”), or it can extend across a wide area to produce general deterioration. Vehicle manufacturers or fleet operators should contact the aluminium supplier in any case of critical working conditions like elevated temperatures or aggressive loads.
EUROPEAN ALUMINIUM ASSOCIATION ALUMINIUM IN COMMERCIAL VEHICLES CHAPTER XI 147 Galvanic corrosion 2.2. Types of aluminium corrosion in commercial vehicles Although highly resistant to corrosion through its natural oxide film, the following types of corrosion can occur in commercial vehicle construction or operation: • Galvanic corrosion • Crevice corrosion • Pitting corrosion • Filiform corrosion 2.2.1. Galvanic corrosion Galvanic or bimetallic corrosion can occur when two different metals (or electroconductive non-metallic materials) are in contact with each other in the presence of an electrolyte. The reason for this type of corrosion is the difference in the electrochemical potential of the two metals. Aluminium is a very electronegative metal and therefore special attention has to be paid when aluminium is used in com- bination with other metals under the presence of an electrolyte (such as water). In an electrochemical reaction, the aluminium is working as an anode and is dissolving, while the other metal retains its integrity. In this case, the aluminium ions react with the oxygen of the water to alumina (Al O ), which 2 3 builds a white layer on the aluminium surface.
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ALUMINIUM IN COMMERCIAL VEHICLES
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Aluminium in Commercial Vehicles ha
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VII. FABRICATION . . . . . . . . .
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CHAPTER II ALUMINIUM IN TRANSPORT 1
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EUROPEAN ALUMINIUM ASSOCIATION ALUM
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CHAPTER III WHY USING ALUMINIUM 1.
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CHAPTER IV FREQUENTLY ASKED QUESTIO
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CHAPTER V ALUMINIUM ALLOYS FOR COMM
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CHAPTER VI DESIGN AND CALCULATION 1
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CHAPTER VII FABRICATION 1. INTRODUC
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aluminium in commercial vehicles - European Aluminium Association

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