Localized Corrosion Studies On Aluminum Alloy 2024-T3 And Its Protective Coating

Aluminum alloy 2024-T3, as a kind of hard aluminum alloy, mainly used for the aircraft structure and many other occasions, has become the most widely used aluminium alloy in aerospace industry. In order to improve the strength of the alloy, a certain way (such as aging heat treatment) is used to introduce second phase particles in the alloy. The second phase particles containing Cu, Fe, Mg, and other elements can improve the mechanical strength, but reduce the corrosion resistance of the aluminum alloy at the same time. The protective method of aluminum alloy 2024-T3 has been relied on a protective coating, i.e., the chromate-containing coating for a long time. Unfortunately, as the most effective corrosion inhibitor, chromate was banned due to its carcinogenic effect to human body. Thus, the development and performance of chromium-free coating become a hot research area for protection of aluminum alloy. Since 1970s, localized electrochemical techniques are introduced in the field of metal's corrosion and protection. Then, the theories and detection techniques have been rapidly developed. In recent years, scanning ion-selective electrode technique (SIET) and scanning vibrating electrode technique (SVET) have been widely used as important tools in the field of localized corrosion. Therefore, it is of great importance to use these localized electrochemical techniques when doing research on corrosion of aluminium alloy 2024-T3 and its protective chromate-free organic coatings.In this study, the coupling electrodes consisted of intermetallic compounds, i.e.,0 (Al2Cu), Al3Fe phase and aluminum wire are used to simulate corrosion of 2024-T3 aluminium alloy. Aluminum alloy 2024-T3 was also used to study the corrosion mechanism. By means of SIET, SVET, SEM and EDS, the mechanism of intergranular corrosion was investigated. Experimental results showed that the 9 phase (Al2Cu) and Al3Fe phase behaved as cathodes in the intergranular corrosion, while aluminum wire acted as anode. S phase (Al2CuMg) of aluminum alloy 2024-T3 dissolved before a phase (Al).In order to study the inhibiting effect of 8-hydroxyquinoline on the corrosion of aluminum alloy 2024-T3, a series of expriments were carried out. First, the coupling corrosion from the coupling electrodes system consisted of 0 phase, Al3Fe phase and aluminum wire was investigated in 0.005 mol·L-1 NaCl solution saturated by 8-hydroxyquinoline. Second, the inhibiting effect of 8-hydroxyquinoline on corrosion of aluminum alloy 2024-T3 was investigated using 0.005 mol·-L-1 NaCl solution saturated by 8-hydroxyquinoline as corrosive medium. The results showed that 8-hydroxyquinoline played an inhibiting effect on corrosion of AA 2024-T3. Finally,8-hydroxyquinoline was doped in a protective coating (Self-assembly nano coating) for protection of aluminum alloy 2024-T3. In the neutral NaCl aqueous solution, electrochemical impedance spectra (EIS), SVET and SEM were used to characterize the performance of self-assembly nano coating. The results showed that the coating containing 8-hydroxyquinoline can effectively reduce the corrosion rate of aluminum alloy 2024-T3.