Study Of Corrosion Behavior And Protection Of Magnesium Alloy Under Thin Electrolyte Layer

Magnesium alloys are considered to be the most potential materials in 21 th century,because of the outstanding properties such as high strength,good damping performance,easy to die-casting,recyclable,and so on.Despite of these excellent properties,magnesium alloys show the poor corrosion resistance in the environment,which limit their further applications.Recent years,researches have paid more attention to the corrosion behavior of magnesium alloys in bulk solution.However,the study on the corrosion behavior of magnesium alloys in the atmospheric environment is less and not sufficient.Meanwhile,the defects of high treatment costs,environmental pollution and other issues are in magnesium alloys surface treatment technologies,so the trend in this field is to research some high efficiency,low toxicity,environmentally friendly surface treatment technologies.The potentiodynamic polarization curves and electrochemical impedance spectroscopy?EIS?were employed to investigate the corrosion behavior of AZ91 D in NaCl,Na₂SO₄,NaHCO₃ solution bulk solution and the thin electrolyte layer,respectively.Results indicated that corrosion rates of magnesium alloy were NaHCO₃>Na₂SO₄>NaCl both in bulk solution and the thin electrolyte layer.This phenomenon could be attributed to that cathodic and anodic corrosion process of magnesium alloys were both inhibited,meanwhile,the corrosion rate in NaHCO₃ solution was the most.The corrosion rates of AZ91 D magnesium alloy tended to decrease with the increasing of the immersing time under thin electrolyte layer,during 72 h impedance monitoring.The corrosion rate in Na Cl bulk solution was slow at the beginning of the corrosion,then the corrosion rate increased gradually,the surface of magnesium alloy occurred fracture under the erosion effect of Cl^-.The corrosion rate changed little and kept stably in Na₂SO₄ bulk solution.Moreover,the activation dissolution of magnesium alloy under NaHCO₃ thin electrolyte layer was obviously inhibited,so the corrosion rate was much lower than that in bulk solution.To study the influence of different cations on the corrosion behavior of AZ91 D in bulk solution and the thin electrolyte layer,NaCl,CaCl₂ and NH4 Cl were selected.The results revealed that the corrosion rates of magnesium alloy were NH₄Cl>CaCl₂>NaCl both in bulk solution and thin electrolyte layer.During 72 h impedancemonitoring,the results revealed that Ca2+ and NH4+ could increased the corrosion rate of magnesium alloy.Moreover,the activation dissolution of magnesium alloy under the NH4 Cl thin electrolyte layer was obviously inhibited and the corrosion rate was lower than that in the bulk solution.The conductive polyaniline?PANI?film was synthesized on magnesium alloy by cyclic voltammetry?CV?.The effect of electropolymerization parameters?scanning mode,applied potential,scan rate and cycle number?on corrosion resistance of PANI were systematically studied.The results indicated that synthetic conditions affected the corrosion resistance of PANI significantly.The best protection performance could be obtained when PANI was synthesized on AZ91 D by CV potential range from-0.2 to 1.8V?SCE?with a scan rate of 30 mV/s for 10 cycles from 0.5 mol/L sodium salicylate solution containing 0.2 mol/L aniline.The morphology of conductive PANI was observed by Fourier Transform infrared spectroscopy?FTIR?and scanning electron microscopy?SEM?,PANI is granular and fibrous structures.