Corrosion Behavior of Aluminum Alloy 6061AA in 3 M Sodium Chloride (NaCl) Solution

Abstract

The research aims to study the CR of aluminum alloy 6061AA in a 3M sodium chloride (NaCl) solution, both before and after SHT, to understand how this treatment affects the alloy’s corrosion resistance. Corrosion is a major challenge for the use of metals in marine and industrial environments, where surface conditions and thermal treatments play a crucial role in enhancing or reducing corrosion resistance. Cyclic polarization test results showed that heat treatment at 530°C for 3 hours led to a decrease in CR, with the corrosion rate increasing from 5.983×10^–3 mm/year to 11.16×10⁻³ mm/year. The most common type of corrosion observed was pitting corrosion. The alloy used in this study, 6061AA, has a known chemical composition. The samples were disk-shaped, polished, cleaned, and then exposed to 3M NaCl solution. They were also subjected to solution heat treatment at various temperatures (150°C and 200°C) for durations of 3 and 4 hours. Electrochemical tests were conducted using a three-electrode setup in 3% NaCl solution to analyze corrosion behavior via potentiodynamic polarization curves. A FESEM was used to examine microstructures and identify corrosion pit formation and distribution of secondary phases. Microstructural analysis revealed that phases like Mg₂Si and CuAl₂ form clearly after aging. Increasing aging time led to the aggregation of precipitates into larger particles, which negatively affected corrosion resistance. Corrosion resistance improved initially with aging time but eventually decreased due to the increased presence of the corrosion-promoting Q phase. The study concluded that two types of precipitates, β, and Q, have opposite effects on corrosion. The β precipitate acts as an anode and protects the matrix, while the Q precipitate promotes corrosion. Thus, the best corrosion resistance was observed in samples aged for 4 hours at 200°C, which had the highest β content and lowest Q content.