Corrosion Resistance of Aluminum Alloy AA2024 with Hard Anodizing in Sulfuric Acid-Free Solution

• Published in: Materials Vol. 15; no. 18; p. 6401
• Main Authors: Miramontes, José Cabral, Gaona Tiburcio, Citlalli, García Mata, Estefanía, Esneider Alcála, Miguel Ángel, Maldonado-Bandala, Erick, Lara-Banda, Maria, Nieves-Mendoza, Demetrio, Olguín-Coca, Javier, Zambrano-Robledo, Patricia, López-León, Luis Daimir, Almeraya Calderón, Facundo
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01.09.2022; MDPI
• Subjects: Aeronautics; Aircraft; Alloy systems; Alloys; Aluminum; aluminum alloy; Aluminum alloys; Aluminum base alloys; Anodizing; Citric acid; Commercial aircraft; Copper; corrosion; Corrosion and anti-corrosives; Corrosion currents; Corrosion potential; Corrosion resistance; Current density; Diamond pyramid hardness; Electrochemical corrosion; Electrochemical impedance spectroscopy; Electrode polarization; Electrolytes; environmentally friendly; Hard anodizing; hard coatings; Humidity; Mechanical properties; Metal fatigue; Morphology; Specialty metals industry; Spectrum analysis; Sulfuric acid; Mexico; United States > US
• ISSN: 1996-1944; 1996-1944
• DOI: 10.3390/ma15186401

In the aeronautical industry, Al-Cu alloys are used as a structural material in the manufacturing of commercial aircraft due to their high mechanical properties and low density. One of the main issues with these Al-Cu alloy systems is their low corrosion resistance in aggressive substances; as a result, Al-Cu alloys are electrochemically treated by anodizing processes to increase their corrosion resistance. Hard anodizing realized on AA2024 was performed in citric and sulfuric acid solutions for 60 min with constant stirring using current densities 3 and 4.5 A/dm2. After anodizing, a 60 min sealing procedure in water at 95 °C was performed. Scanning electron microscopy (SEM) and Vickers microhardness (HV) measurements were used to characterize the microstructure and mechanical properties of the hard anodizing material. Electrochemical corrosion was carried out using cyclic potentiodynamic polarization curves (CPP) and electrochemical impedance spectroscopy (EIS) in a 3.5 wt. % NaCl solution. The results indicate that the corrosion resistance of Al-Cu alloys in citric acid solutions with a current density 4.5 A/dm2 was the best, with corrosion current densities of 2 × 10−8 and 2 × 10−9 A/cm2. Citric acid-anodized samples had a higher corrosion resistance than un-anodized materials, making citric acid a viable alternative for fabricating hard-anodized Al-Cu alloys.