The Study Of Inhibitors For AZ31 Mg Alloy In Sodium Chloride Solution

Magnesium and its alloys are recognized as one of the lightest structural materials for automotive and electronics industries because of their low density,high specific strength,good thermal conduction,and electro-magnetic wave shielding capacity.But their applications in many industrial fields are limited due to their poor corrosion resistance.Adding inhibitors into electrolyte,the corrosion with the respect to magnesium alloy will be retarded efficiently.Compared with alloying,surface modification and coating,this method does not change the shape and size of components,for which the application prospect of inhibitors is wide.Therefore,it is a hot spot in the field of magnesium alloys to screen inhibitors and study their corrosion inhibition efficiency.The inhibiting effect of addition of inhibitors on corrosion of Mg alloy AZ31in 3.5wt%NaCl solutions was investigated by electrochemical tests?including Potentiodynamic Polarization,Electrochemical impedance spectroscopy measurements and Electrochemical Noise?,Scanning Electron Microscope and Energy Dispersive Spectrometer.Five kinds of inhibitors including 1-Butyl-3-methylimidazolium tetrafluoroborate?[BMIM]BF₄?,Caprylyl glucoside?C₈APG?,Konjac Glucomannan?KGM?,Indigo Carmine,Sodium Citrate?NaCA?were added into 3.5wt%NaCl solutions to analysis the inhibiting efficiency on corrosion of Mg alloy.The obtained results showed that two inhibitors,C₈APG and NaCA,can restrain the corrosion of AZ31 Mg alloy efficiently,the optimal inhibition efficiencies are 58.2%and 85.6%,respectively.After comprehensive consideration of the inhibition efficiency of several kinds of organic inhibitors and whether they are green or not,two kinds of inhibitors?C₈APG and NaCA?,were selected to combine with inorganic corrosion inhibitor sodium phosphate?SP?and investigated the inhibition on AZ31 Mg alloy.The following conclusions were obtained:?1?The optimal inhibition efficiency in terms of corrosion of AZ31 alloy was yield in 3.5wt%NaCl solution containing 6g/L C₈APG and 1g/L SP concentrations,and the inhibition efficiency is 88.6%.The inhibiting mechanism could be attributed to the formation of a compact and protective film due to the physical absorption of C₈APG with Mg?OH?₂ and Mg₃?PO₄?₂ on the Mg surface.?2?When joint-addition of NaCA and SP,the inhibition efficiency would increase obviously.The optimal inhibit efficiency can reach to 95.2%,when 3mM NaCA and 3mM SP are jointly added into 3.5wt%NaCl solution,due to the formation of a compact and protective film on the AZ31 Mg alloy surface.Chemical composition study elucidated that such a protective film contains not only conventional magnesium hydroxide,but the formation of Mg₃?PO₄?₂ and CA-Mg compounds.