Corrosion behaviour of aluminium alloys

Aluminum is a light metal with a density of 2.7, about a third of that of steel (7.8). This is why aluminum alloys are widely used in the construction, mechanical engineering and transportation industries (automotive, aeronautics, naval...) to lighten structures.

Aluminum and its alloys also have a high thermal conductivity compared to steel, making them excellent materials for heat exchange devices (radiators, heat exchangers, refrigerators, air conditioners, etc.). What's more, their good electrical conductivity and low weight mean that they are widely used in the manufacture of electrical cables, especially large cross-section cables.

The third characteristic of aluminum is its ease of processing under reasonable temperature and mechanical stress conditions (casting, extrusion, rolling, stamping, etc.). Combined with its suitability for surface treatments, this property makes it a highly attractive material for complex mechanical parts with decorative functions (doors and windows, lighting fixtures, street furniture, household items, etc.).

Aluminum is also one of the metals with good corrosion resistance, and can be brought into contact with a variety of environments: rural, urban or marine atmospheric conditions, acidic environments in contact with condensates in heat exchangers, in seawater... What's more, aluminum alloy surfaces can easily appear shiny and develop colorless or white corrosion products. This is an advantage over steels, where surface tarnishing can quickly lead to the appearance of highly colored, often unsightly products.

However, pure aluminum and very low-alloy (> 99% mass.) alloys have very poor mechanical properties compared to low-alloy steels. Alloys are therefore necessary for many applications. Few metals are soluble in aluminum, and the addition of alloying elements inevitably leads to the formation of multiple intermetallic phases (IM) . The improvement of processes through various heat treatments and the search for new phases have led to new lightweight alloys with high mechanical properties, enabling very high mechanical strengths to be achieved. Nevertheless, the presence of intermetallic phases reduces the corrosion resistance of aluminum materials, sometimes quite significantly. As a result, the corrosion behavior of aluminum alloys is highly varied and highly variable.

In this article, we begin by describing the corrosion properties of pure aluminum: thermodynamics,...