Effect of Nitrate and Galvanic Couple on Crevice Corrosion Behavior of 7075-T651 Al-alloy in Neutral NaCl Solution
The effect of the presence of nitrate and galvanic couple on the crevice corrosion behav-ior of 7075-T651 Al-alloy in 3.5％NaCl solution is investigated by the electrochemical tests and surface analysis techniques.The results indicate that the nitrate as an oxidizing agengt could promote the forma-tion of passive film,so that inhibit the corrosion of the Al-alloy.However,when there is a formed crevice on the Al-alloy in a solution without nitrate,inside the crevice corrosion is hard to occur and develop,in the contrast,in a solution with the presence of nitrate,which could be reduced forming NH3,the later agent may accumulate inside the crevice and selectively dissolve the copper particles,thereby induced the nucleation of pitting corrosion,afterwards,further promoted the propagation of crevice corrosion.After coupling with 304 stainless steel,a large Galvano-corrosion driving force is generated between the elec-trodes inside and outside the crevice,which accelerates the metal dissolution and solution deterioration process in the crevice,resulting in much more serious crevice corrosion in the solution with nitrate.
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