The Corrosion Mechanism Of 2099 Al-Li Alloy Was Studied By Scanning Electrochemical Microscopy

Aluminum-lithium alloy is one kind of light alloy material with high specific strength and high modulus of elasticity.It is used widely in aerospace,automotive,robotics and other fields.However,because of the anisotropy of Al-Li alloys,the structural materials are prone to corrosion in the marine atmosphere.The use of corrosion inhibitors has been the most practical and convenient way to deter and curtail this phenomenon.The corrosion behaviors of 2099 Al-Li alloy in NaCl solution and seawater were investigated by polarization curve test,AC impedance test and SECM scanning.The inhibitory effect of imidazoline corrosion inhibitor on the corrosion of alloy were studied.The results were showed as following:(1)The corrosion behaviors of 2099 Al-Li alloy in NaCl solution were studied by polarization curve and AC impedance spectroscopy.The results showed that the corrosion of Al-Li alloy increased with the concentration of salinity,the corrosion depth increased and the corrosion resistance decreased.In different concentrations of NaCl solution,the shapes of the impedance spectrum of the alloy were semicircle with a reduced internal radius.The solution resistance of the 2099 Al-Li alloy decreased in NaCl solution and the charge transfer resistance decreased from 67300Ω/cm~2 to17400Ω/cm~2.The corrosion resistance of the alloy decreased.In 3 wt%NaCl solution,change the solution pH(3~11),the corrosion current density was 7.185μA/cm~2 at pH=3,the corrosion current density was 153.6μA/cm~2 at pH=11.The corrosion resistance of the alloy under alkaline conditions was worse.With the increase of pH value,the charge-transfer resistance of the alloy decreased,and the corrosion of the oxide film on the metal surface by Cl~-in the solution aggravated.The polarization behavior and impedance behavior of 2099 Al-Li alloy in seawater were studied.The results were showed that the polarization curves and AC impedance spectra of alloy in seawater were the same as those in NaCl solution,and the corrosion mechanisms were similar with that in swe.water(2)Imidazoline corrosion inhibitor was added into 3 wt%NaCl solution.The behaviors of corrosion inhibitor on 2099 Al-Li alloy were investigated by polarization curve and AC impedance spectroscopy.The results showed that the corrosion rate of the alloy decreased from 0.058 mm/a to 0.0289 mm/a with the corrosion inhibitor concentration increased from 0.001 mmol/L to 0.01 mmol/L.The corrosion inhibitor efficiency changed with the concentration of corrosion inhibitor increased.With the charge transfer resistance in the impedance spectrum increasing,the corrosion resistance of the alloy increased.The nitrogen-containing heterocyclic ring of imidazoline corrosion inhibitor can form adsorption type protective film on the alloy surface.(3)The micro-corrosion behaviors of 2099 Al-Li alloy in different immersion time and different electrolyte were studied by scanning electrochemical microscope(SECM).The results showed that the initial corrosion of 2099 Al-Li alloy was dominated by point corrosion.With the increase of immersion time,the corrosion of the alloy was aggravated and the alloy matrix dissolved to form new corrosion pits.Due to the high Cl~-concentration in the seawater,the corrosion was more serious.Adding imidazoline corrosion inhibitor,the activation points of the alloy surface decreased,it showed that the corrosion of the alloy was inhibited.(4)The corrosion products of the alloys in different electrolytes were studied by SEM and XRD.The results showed that the products of 2099 Al-Li alloy in NaCl solution and seawater were not different,They were mainly the oxides of aluminum.The nitrogen structure of the imidazoline inhibitor restricted the dissolution of the alloy,had a protective effect on the alloy.