Galvanic Corrosion of Titanium and Aluminum Couplings in Simulated Marine Atmospheric Environment
Titanium alloys and aluminum alloys are two of the most widely used lightweight metallic structural materials in the aviation industry.The sum of the two can reach 60%-80%of the overall material of the aircraft.In view of the complex internal structure of the aircraft and the large number of parts,the contact between dissimilar metals is very common,among which titanium-aluminum couplings are the most prevalent.The purpose of this paper is to investigate the galvanic corrosion behavior of titanium and aluminum couplings for aircraft structures in the marine atmospheric environment,and to theoretically analyze the difference of galvanic corrosion at different positions of structural parts,so as to further enrich the galvanic corrosion mechanism between titanium and aluminum.In order to compare the effects of immersion and thin liquid film test conditions on the corrosion process,potentiodynamic polarization curves,zero resistance current test(ZRA)and neutral salt spray test were used.Finite element modeling(FEM)was used to characterize the influence range of galvanic action on the surface of titanium and aluminum,and also predict the local corrosion.Finally,the corrosion morphology and weight loss test were conducted to verify it.In the simulated marine atmospheric environment,the cathodic reduction reaction rate on the surface of titanium and aluminum alloy was higher than that in the immersion condition,and the galvanic current density between the two metals was increased from 1.52 μA/cm2 to 11.00 μA/cm2.In addition,when the area ratio of titanium to aluminum was 1∶1 under the ideal condition,the galvanic potential between titanium and aluminum(Eg=-0.70 V,vs.SCE)was close to the self-corrosion potential of aluminum alloy(Ecorr,Al=-0.68 V,vs.SCE),and away from the sel-corrosion potential of titanium alloy(Ecorr,Ti=-0.30 V,vs.SCE).However,combined with the effect of solution resistance under actual condition,the influence range of galvanic action on these two metals were different.As for the cathodic titanium alloy,the high cathodic polarization potential of about-400 mV resulted in galvanic effects throughout the whole titanium parts of the couplings.As for the anodic aluminum alloy,the low anodic polarization potential of 20 mV lead to a short influence distance of galvanic effect on the aluminum surface,only 10-15 mm.But the anodic reaction of aluminum alloy in chloride-containing corrosive media was in an active dissolved state,such a small polarization potential could also cause a large change in corrosion rate of aluminum.Therefore,the corrosion at the aluminum alloy boundary in direct contact with titanium is the most serious.It is worth noting that the corrosion depth of anodic aluminum alloy at different boundary positions may also differ by more than 4 times,which is mainly related to the cathode/anode area ratio within the influence range of galvanic action.And the aluminum part of the titanium-aluminum couplings that are not affected by galvanic action is still subject to relatively serious self-corrosion.
titanium alloyaluminum alloygalvanic corrosionFEMatmospheric corrosionthin liquid film
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