Anti-corrosion protections of aluminum alloys

The use of aluminum alloys has grown due to their lightness and resistance to corrosion. However, pure aluminum and low-alloy alloys remain highly malleable and have limited mechanical strength.

The industrial development of these alloys therefore required improvements in the mechanical properties of the aluminum material (tensile strength, fatigue strength, etc.). After the development of the Hall-Héroult metallurgical process at the end of the 19th century, aluminum became a metal of interest with the publication of Alfred Wilm's German patent in 1909 on Al-Cu-Mg alloys, known as "Duralumin", which marked the beginning of the development of aluminum alloys with high mechanical strengths, comparable to those of low-alloy carbon steels. These alloys were rapidly put to use in mechanical engineering and transport, particularly in the aeronautical sector.

However, as early as the 1920s-1930s, deterioration problems with Al-Cu-Mg alloys used in aeronautics were quickly detected by the National Advisory Committee for Aeronautics (NACA) in the USA (which became the National Aeronautics and Space Administration – NASA – in 1958). The addition of alloying elements to aluminum leads to the formation of intermetallic phases, drastically reducing aluminum's resistance to corrosion. Chromate-based anti-corrosion surface treatments, already used on steels, followed by anodizing treatments, were then successfully applied to aluminum alloys to improve their service life.

Today, numerous anti-corrosion treatments enable aluminum alloys to be used in highly corrosive industrial atmospheres (rich in SO ₂ , NaCl in the transport industry), or in contact with acidic or oxidizing media (disinfectant solutions, acids in the food industry...).

Since the early 2000s, European regulations on the use of chemicals (REACH: Registration, Evaluation and Authorisation of Chemicals) and standards on industrial effluent discharges have necessitated the search for new surface treatments based on non-toxic products (chrome(VI)-free) and without heavy metal cations (such as the Ni ²⁺ ion). This also means intensifying processes to reduce aqueous effluents and then treating the remaining effluents, thereby increasing production complexity and costs. At the same time, the demand for multifunctional coatings meeting multi-criteria specifications has become essential to ensure the competitiveness of many industrial activities. Finally, societal demands to improve the durability of various industrial products, particularly metal parts, require constant improvements in anti-corrosion protection. As a result, a wide range of protective processes has appeared on the...