Study Of Inhibition Effects On Aluminum Alloy With Rare Earth And Organic Mixed Inhibitors

Corrosion occurs frequently on aluminum alloys while there’s aggressive ion such as chloride ion (Cl-) in the environment, especially when it is alkaline. The corrosion on aluminum alloys had caused serious damage and great loss to society. It is significantly important to find out the methods of preventing and controlling corrosion by researching the process and mechanism of the aluminum alloys’corrosion in alkaline environment. The use of inhibitors is a highly efficient and common method to prevent the corrosion of metals.Potentiodynamic polarization, EIS, FTIR, XPS and SEM-EDS were applied to study the corrosion behavior of 2024-T3 aluminum alloy in the solution of 0.01 mol·L-1 NaCl and mixed inhibitors of rare earth salt (LaCl3 and CeCl3) and organic salt (SDBS) with final pH of 10. The inhibition effects and mechanisms of mixed inhibitors on 2024-T3 aluminum alloy were also studied. The main conclusions are as follows:(1) In the solution of 0.01 mol·L-1 NaCl with final pH of 10, addition of rare earth salt (LaCl3 and CeCl3) and SDBS can slow down the uniform corrosion rate, indicating that mixed inhibitors have a good inhibition effect on uniform corrosion.0.1 g·L-1 LaCl3 and 0.42 g·L-1 SDBS are the best lanthanum salt mixed inhibitors,0.1 g·L-1 CeCl3 and 0.28 g·L-1 SDBS are the best cerium salt mixed inhibitors. Both of them have the best inhibition effect of pitting corrosion in short time.(2) In the solution of 0.01 mol·L-1 NaCl with final pH of 10,0.1 g·L-1 LaCl3 and 0.42 g·L-1 SDBS mixed inhibitors have the effect of inhibiting pitting corrosion within 12 hours’ immersion, but after 24 hours’immersion, the effect weakened. After 24 hours’immersion,0.1 g·L-1 CeCl3 and 0.28 g·L-1 SDBS mixed inhibitors’effect of inhibiting pitting corrosion also weakened. But, with 24 hours’immersion, the addition of lanthanum or cerium salt best mixed inhibitors still has quite strong inhibition to uniform corrosion.(3) EIS test shows that with the extension of immersion time, the addition of lanthanum or cerium salt best mixed inhibitors in the solution of 0.01 mol-L"1 NaCl with final pH of 10 make the film on aluminum alloy surface has good protective effect and become stronger gradually. But damage in pores in the film of aluminum alloy surface is quite serious, the existence of defects makes the pitting corrosion form. Finally it’s manly the occurrence of pitting leads that the inhibition effect of uniform corrosion is weakened.(4) The addition of rare earth salt and SDBS mixed inhibitors inhibit uniform corrosion and mitigate pitting corrosion. During the initial stage of immersion, DBS" adsorbs on substrate surface by electrostatic attraction to form a protective film, and promotes the formation of Al(OH)3 with higher binding energy to make substrate to be passivated. At the same time, rare earth oxides/hydroxides deposite on substrate surface. The final formed film provides good protective effect on substrate. But with the extension of immersion time, the absorbed DBS- on substrate surface desorbs and solution infiltrates into the substrate surface gradually. On S phase, as the noticeable galvanic effect between Al2CuMg particles and the aluminium alloy surrounded the particles leads to the result that the aluminium alloy surrounded the S phase dissolved preferentially, and the same with aluminum and magnesium On S phase. Finally corrosion holes form around the residual rich copper phase and damage the protective film near the small holes further. Due to the formation of a large number of corrosion holes, the substrate surface comes into activation corrosion. However, to some extent, the existence of the protective film still inhibits the occurrence and growth of pitting corrosion, especially sulfur-containing substances such as DBS" and rare earth organic compounds (La(DBS)3 and Ce(DBS)3) may deposite on the S phase preferentially.