| The addition of Li to Al alloy can reduce its density,which has high specific strength,good fatigue crack growth performance and good ductility.Al-Li alloy,with high activity Li,is higher susceptible to local corrosion in corrosion circumstance,such as pitting,inter-granular corrosion and exfoliation corrosion.Improving of corrosion resistance is significant to develop mechanical properties of Al-Li alloy and improve the stability and reliability of the parts.In the methods of improving the corrosion resistance of Al alloy,anodic oxidation is widely used because of its simple process,convenient operation and low cost.2198 Al-Li alloy was treated by direct current?DC?anodizing and pulse anodizing in H2SO4 solution in this paper.The optimization of oxidation parameters was determined by observing morphologies,testing the thickness and microhardness of anodic oxidation film.Moreover,corrosion resistance of the oxide film was measured by polarization plot and neutral salt spray test.The obtained results were as follows:?1?DC anodic oxidation process:the optimized oxidation parameters for 2198 Al-Li alloy was 18%H2SO4 solution,16V oxidation voltage and 60min.The composition of anodic oxidation film obtained at this condition was mainly composed of Al2O3 and Li oxide.Together,trace Cu and S elements accumulated and existed in the film.Compared with 2198Al-Li alloy,corrosion current density of this alloy after anodic oxidation decreased one order of magnitude.Thus,corrosion resistance of 2198 Al-Li alloy could be improved by DC anodic oxidation.?2?Influence of temperature to anodic oxidation:With the increasing of oxidation temperature,the microhardness of anodic oxidation film decreased;its thickness and corrosion resistance initially increased and then decreased.The anodic oxidation film obtained at the temperature of 20?had higher corrosion resistance.?3?Pulse anodic oxidation process:the anodic oxidation film on 2198 Al-Li alloy was obtained at 16V/10ms forward voltage and 2V/2ms reverse voltage.Oxidation time was60min.Corrosion current density of oxidation film was 8.540×10-8 A/cm2,which was higher than that of DC anodic oxidation.Proper reverse voltage during anodic oxidation process was contributed to improve corrosion resistance of the oxidation film. |
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