Research On Crevice Corrosion Behaviour Of5083and6061Aluminum Alloys

The5083and6061aluminum alloys are commonly used in marine applications wherelow density materials, good mechanical properties and better resistance to corrosion aredesired. But some corrosion problems of aluminum alloys hampered the development of themarine industry. These materials may suffer crevice corrosion during their service. So it hasimportant theoretical and practical significance for the further understanding of its mechanismto research the crevice corrosion behavior of5083and6061aluminum alloys. The researchresults of this paper are as follows:A series of microelectrode was constructed based on an iridium pH microelectrode andan Ag/AgCl microelectrode, and was applied to simultaneously monitor the potential, pH andchloride ion concentration in a crevice simulating of AA5083and AA6061.The results showed an decrease in pH and a increase in chloride ion concentration fromopening to deep in the crevice. This phenomenon was very evident in5083aluminum alloys.While the evident potential gradient resulting from the IR potential drop was concentrated in6061aluminum alloys. This indicated that the main mechanism for6061Al-Alloy was IRvoltage switch, while the main mechanism for5083Al-Alloy was critical crevice solutiontheory.Electrochemical noise（EN） was employed to study the crevice corrosion behaviour andits mechanism. The crevice corrosion behavior of5083and6061Al-Alloy in3.5%NaClsolution system could be divided inio two stages: an incubation stage, and a stabledevelopment stage. The crevice corrosion rate of5083Al-Alloy was relatively lower than6061Al-Alloy. Subsequently, statistical parameters derived from shot noise theory wereobtained and the corrosion type of5083and6061Al-Alloy was different. The corrosion of5083Al-Alloy was mainly uniform corrosion and transferred to severe localized corrosionwith the increasing of crevice depth. But the corrosion of6061Al-Alloy was severe localizedcorrosion.The influence of the major precipitates on the corrosion behavior of5083and6061Al-Alloy was presented in this paper. For5083Al-Alloy，a slightly noble potential wasobserved for Al-Fe-Mn and slightly lower potential for Al3Mg2compared to the matrix.Itindicated micro-galvanic corrosion was not serious causing a further reduction in pH and an increase in the rate of influx of anions into the crevice. But for6061Al-Alloy, the largeprecipitates Al-Si-Fe resulted in a large noble potential compared to the matrix. Mg2Si and wasexpected to be preferentially attacked during corrosion due to its significantly lower potentialcompared to the matrix. Huge potential difference caused rapid deterioration of the metalwithin the crevice, with possible structural failure of the metal. In this case, the metal baredand potential reduced. The difference of5083and6061Al-Alloy on microstructure meanttheir corrosion severity and mechanism was different.