Study On Inhibition Mechanism Of Environmental-Friendly Inhibitors For Magnesium Alloys

Magnesium and its alloys are the lightest nonferrous structural metals and have a promising application prospect in automotive and aeronautic industry and so on. However, magnesium alloys are unstable and corrode easily in many aqueous media because of their high chemical and electrochemical activity. These have restricted the further application of magnesium alloys. The addition of inhibitors is a simple and effective method for inhibiting the corrosion of metals. Therefore, the environmental-friendly inhibitors for magnesium alloys in 3.5%NaCl solution and their inhibition mechanism were studies in this paper. The obtained results would be important significance in guiding the selection and use of inhibitors for magnesium alloys in NaCl media.The electrochemical methods, such as electrochemical impedance spectroscopy (EIS) and Tafel polarization curve, were used to investigate the corrosion behavior of AZ31 magnesium alloy in 3.5%NaCl solution at different temperatures. The inhibition of sodium benzoate, sodium dodecylbenzenesulphonate and sodium tungstate for AZ31 magnesium alloy in 3.5%NaCl solution was mainly studied. The inhibition for each inhibitor was estimated according to the electrochemical parameters of each inhibitive system. The adsorption of inhibitor onto AZ31 magnesium alloy surface was explained by using adsorption equations and the corresponding thermodynamic parameters were calculated. The inhibition mechanisms of different inhibitors were discussed combining with the results of scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). The inhibition of the conventional inhibitors of magnesium alloy—fluoride and dichromate was compared with the inhibitors studied in this paper. The results were showed as follow.AZ31 magnesium alloy was easily corroded and corroded more seriously with the increase temperature.Sodium benzoate acted as an anodic inhibitor for AZ31 magnesium alloy in 3.5%NaCl solution. The adsorption of sodium benzoate onto AZ31 magnesium alloy surface obeyed the Temkin adsorption isotherm and the adsorption process was a spontaneous, exothermic process accompanied by an increase in entropy. Sodium dodecylbenzenesulphonate acted as a mixed-type inhibitor mainly inhibited the anodic process for AZ31 magnesium alloy in 3.5%NaCl solution. Within the range of tested concentrations, the inhibition efficiency of sodium dodecylbenzenesulphonate had a threshold value at lower temperatures and increased with the increase concentration at higher temperatures. The adsorption of sodium dodecylbenzenesulphonate onto the AZ31 magnesium alloy surface almost obeyed the Langmuir adsorption isotherm at higher temperatures and the adsorption process was a spontaneous, exothermic process accompanied by a decrease in entropy. Sodium tungstate acted as an anodic inhibitor for AZ31 magnesium alloy in 3.5%NaCl solution. Within the range of tested concentrations, the inhibition efficiency of sodium tungstate had a threshold value at lower temperatures and increased with the increase concentration at higher temperatures. The adsorption of sodium tungstate onto the AZ31 magnesium alloy surface obeyed the Langmuir adsorption isotherm and the adsorption process was a spontaneous, exothermic process accompanied by a decrease in entropy.Compared with conventional inhibitors of magnesium alloy—fluoride and dichromate, the inhibitors studied in our work showed their advantages of high inhibitive efficiency and environmental-friendly properties and would be widely used for corrosion inhibition of magnesium alloy.