Corrosion Assessment of Arc Thermal Sprayed Al and its Alloy Coatings in Aggressive Environments: An Overview

Arc thermal sprayed coatings have a wide range of applications, including corrosion resistance, wear resistance, thermal barriers, and electromagnetic pulse protection. However, these coatings often suffer from significant defects and pore formation, which can reduce their overall effectiveness. This overview focuses on the corrosion resistance properties of Al and its alloys. Al coatings demonstrate good corrosion resistance in marine environments due to the formation of sparingly soluble corrosion products on the surface. When Zn is alloyed with Al, the initial corrosion resistance decreases due to an increased number of pores. However, over extended exposure, these coatings exhibit excellent corrosion resistance as corrosion products fill the pores, providing barrier protection. Additionally, incorporating 5 wt.% Mg in Al coatings enhances bond adhesion and improves corrosion resistance in aggressive environments. To further reduce porosity and enhance corrosion resistance, the use of phosphate-based eco-friendly pore sealing agents is discussed. Optimizing the amount of phosphate during treatment is crucial, as it significantly reduces porosity and enhances corrosion resistance. Both insufficient and excessive amounts of phosphate can deteriorate the coating, while the optimal amount improves corrosion resistance over prolonged exposure to aggressive conditions.