| Today,with more emphasis on energy conservation,emission reduction and environmental protection,magnesium alloy has great development potential and has a wide range of applications in aviation,aerospace,automotive and other fields.Since magnesium has an electrode potential of about-2.37 V,which is the lowest among all structural metal materials,and the oxide film formed on the surface has poor protection performance,magnesium alloy has poor corrosion resistance and is prone to galvanic corrosion when connected with other metals.Therefore,it is very important to understand the corrosion mechanism of magnesium alloys and study the methods to inhibit the corrosion of magnesium alloys.In many research on corrosion protection of magnesium alloys,adding corrosion inhibitor to corrosion medium is a very simple and effective method.In this paper,the effects of sodium benzoate corrosion inhibitor and the combination of sodium benzoate corrosion inhibitor and sodium silicate corrosion inhibitor on the corrosion performance of Mg-9Li-1Zn magnesium lithium alloy(LZ91)in 3.5 wt.% Na Cl solution were studied.The corrosion inhibition efficiency of the inhibitor was detected by hydrogen evolution test and electrochemical test,and the insitu corrosion was observed.The corrosion inhibition mechanism of LZ91 magnesium lithium alloy was discussed by quantum chemistry calculation and molecular dynamics simulation calculation.The results of the experiment are as follows:The results of hydrogen evolution test and electrochemical test show that the corrosion of LZ91 magnesium lithium alloy can be inhibited by adding sodium benzoate(SB)corrosion inhibitor in the corrosion solution of 3.5 wt.% Na Cl,and the corrosion inhibition effect is the best when the corrosion inhibitor concentration is0.1M.In the initial in-situ corrosion observation,a large amount of corrosion occurs in the vicinity of the α-Mg phase of LZ91 magnesium lithium alloy at first,and the corrosion of the alloy can be inhibited by adding 0.1M sodium benzoate corrosion inhibitor.The results of energy dispersive analysis(EDS)and Raman spectroscopy(Raman)tests show that the corrosion inhibitor will concentrate on the α-Mg phase.After long-term immersion in the corrosion solution with sodium benzoate,the corrosion layer on the alloy surface is more compact according to the results of scanning electron microscope(SEM).In addition,the adsorption of corrosion inhibitor on the alloy surface was proved by X-ray photoelectron spectroscopy(XPS).The results of quantum chemistry calculation indicate that the C element on the benzene ring of SB molecule and the O element on the carboxyl group have high reactivity.The results of molecular dynamics simulation show that SB molecule is adsorbed on the surface of magnesium nearly parallel.Sodium silicate(SS)corrosion inhibitor was used to compound sodium benzoate.The electrochemical test results showed that the corrosion inhibition efficiency was the best when 0.1M SB was mixed with 0.015 M SS.In situ corrosion observation,it was found that the number of bubbles on the surface of LZ91 magnesium alloy was significantly reduced and the growth was slow after adding the compound corrosion inhibitor to the corrosion medium,which significantly inhibited the corrosion of the alloy.The SEM and EDS analysis showed that Si elements were aggregated at the corrosion point,and C and O elements were also detected.The macroscopic morphology observation and SEM analysis of the sample surface after long-term immersion show that the compound corrosion inhibitor has better corrosion inhibition effect.The adsorption of SB and SS on LZ91 magnesium lithium alloy surface was confirmed by Fourier Transform infrared spectroscopy(FTIR)and XPS analysis.The molecular dynamics simulation results show that when only SB molecules are added to the corrosion solution,the adsorption energy of SB in the corrosion solution is-16.4k J/mol,and the adsorption capacity of SB on the alloy surface is weak.However,when SB and SS molecules are added to the corrosion solution,the adsorption energy of SB in the solution increases to-35.5 k J/mol.According to the results of the radial distribution function(RDF),the distance between the active atoms on SB and Mg O is shortened,and the adsorption type changes from the physical adsorption with weak adsorption to the stable chemical adsorption,which is conducive to increasing the adsorption energy and improving the corrosion inhibition efficiency. |
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