Metallurgical and Physical Factors Controlling the Multi-functional Corrosion Properties of Pulsed Thermal Sprayed Al-Co-Ce Coatings

High density, low porosity Al-Co-Ce metallic coatings have been successfully applied to AA 2024-T351 substrates using a pulsed thermal spray (PTS) process in thicknesses ranging from 100-500 mm. The three proposed modes of corrosion protection brought about by the coating (e.g., a localized corrosion barrier, a sacrificial anode to supply cathodic protection of any exposed AA 2024-T351, and active inhibitor release and protection of AA 2024-T351) have been verified to function simultaneously in dilute chloride solutions. The localized corrosion properties of the PTS applied coating samples were not equal to the fully amorphous melt spun ribbons even when ribbons were produced from feedstock powders. This inferior behavior in coatings was traced to various microstructural and physical defects (e.g., the formation of intermetallic particles, a non-amorphous structure). However, this inferior behavior can not be attributed to feedstock powder composition since melt spun ribbons made from feedstock powders had excellent localized corrosion properties. As indicated by salt fog testing and galvanic and chemical coupling experiments, PTS coatings provided sacrificial anode-based cathodic protection and provided chemical protection afforded by Ce³⁺ release and migration to exposed 2024-T351. Salt fog testing and open circuit experiments demonstrated that the PTS coating acted as a sacrificial cathode to AA 2024-T351 due to the success of as-deposited PTS lap-joint samples and sustained Al-Co-Ce open circuit potentials below that of AA 2024-T351. Low pH, low chloride concentration experiments, in which Al-Co-Ce coatings are both galvanically coupled and uncoupled to AA 2024-T351, display a reduction in corrosion on the AA 2024-T351, demonstrating that the sacrificial anode-based cathodic protection and inhibitor release capabilities of the PTS coatings have been achieved. These results collectively suggest viable, multifunctional performance in spray applied Al-Co-Ce alloys.