Corrosion mechanisms and behavior of a P-130x Gr/6063 A1 composite in aqueous environments

The corrosion mechanisms and behavior of a P-130x graphite fiber reinforced 6063 aluminum composite laminate were studied. Electrochemical and total immersion tests were performed on the composite in 3.5% sodium chloride and 5.0% sodium sulfate solutions. The effects of pH, the presence of sulfite ions, various heat treatments, and electrolyte aeration were investigated. Some tests were also performed on control monolithic 6063 aluminum specimens. Immersion tests showed that when graphite fibers are exposed simultaneously with the matrix, then galvanic coupling is the principal corrosion mechanism in this composite. However, if the composite cross sectional edges are sealed from contact with the environment, then pitting attack of the surface foils becomes the principal mode of attack, especially in harsh environments (chloride and sulfite ions present in addition to low pH). This form of attack can eventually lead to galvanic corrosion. Low pH and the addition of sulfite ion significantly increase the susceptibility to localized corrosion and the rates of both general and galvanic corrosion. Progressive aging of the composite matrix decreases general corrosion rates in deaerated solutions. Electrolyte aeration results in a significant reduction in the composite's resistance to all forms of corrosion.