Research On Inhibitors For The Crevice Corrosion And Mechanism Of Two Aluminium Alloys In Seawater

Corrosion inhibitors have been proven to be an effective way to restrain the crevice corrosion of aluminum alloys in seawater.The effect of six inhibitors including ammonium molybdate((NH₄)₆MO₇O₂₄),cerium chloride(CeCl₃),lanthanum chloride(LaCl₃),8-hydroxy quinolin(C₉H₇NO),salicylaldoxime(C₇H₇NO₂) and N-Allyl thiourea(C₄H₈N₂S) on the crevice corrosion of 2024 alumium alloy in seawater was studied in this paper.The concentrations of several inhibitors were investigated by immersion in seawater,and the surface micrographs after immersion were observed by scanning electron microscopy(SEM) and atomic force microscope(AFM),and the corrosion films were analysed by EDAX,and the corrosion mechanism was discussed by potentiodynamic polarization and electrochemical impedance spectroscopy(EIS). The results revealed that the(NH₄)₆Mo₇O₂₄,C₇H₇NO₂ and C₄H₈N₂S could not restrain the crevice corrosion of 2024 aluminum alloy in seawater.It is because that corrosion product films formed on the inside and outside of the crevice have great difference, which increasing power of the corrosion reaction.However,when the seawater was in the presence of CeCl₃,LaCl₃ and C₉H₇NO,the films of the inside and outside of crevice were both uniformity and compact,which lead to a lower power for the occurrence of crevice corrosion,and the susceptivity of crevice corrosion for aluminum alloy in seawater was reduced.The concentrations of complex inhibitors composed of CeCl₃,LaCl₃ and C₉H₇NO were decided by using orthogonal experiments.The results showed that the inhibitor efficiency of complex inhibitors were greater than the single inhibitor.When the concentrations of the three compounds of CeCl₃,LaCl₃,8-hydroxy quinolin were 1.0, 1.5 and 0.02 g/L in seawater,respectively,the inhibitor efficiency was 90.52%,and it was the most greatest.The crevice corrosion could not take place.It was because that the adsorption characteristic of 8-hydroxy quinolin,it could be adsorbed on the weak place of the corrosion product formed by CeCl₃ and LaCl₃,and the films became the greater uniformity,which increasing the resistance of crevice corrosion in seawater.The CeCl-3,LaCl₃ and C₉H₇NO mixture have also used as inhibitor of 7A52 alloy. The result revealed that the compounds improve the corrosion resistance of crevice, which implying that the complex compounds have widely application.Thereforce,the mixture may be applied widely as the crevice corrosion inhibitors of aluminum alloys in seawater.