Research On Low Voltage Micro-arc Oxidation Of AZ51Magnesium Alloy

Magnesium alloys are widely used in many areas because of their excellent properties,such as low density,high specific strength and specific rigidity,good damping and electromagnetic shielding performance. However, the corrosion resistance of magnesium alloy is very poor,which has badly limited its application.Usual surface treatment methods,for example,chemical oxidation and anodic oxidation,are able to protect magnesium alloy,but its corrosion resistance and external appearance cannot meet needs of applications.Micro-arc oxidation(MAO) is a new surface treatment technology,which can produce a ceramic coating of high hardness,and corrosion resistance on the surface of magnesium alloys.The research is based on AZ51magnesium alloys,and uses low ac voltage MAO technology to get compact coatings on the surface of magnesium alloy.This solved two key questions,one is long processing time,another is big holes on coating surface. The relationship between treatment parameters and coating thickness were investigated,the morphology and corrosion resistance of different thickness of coatings were analyzed.The results show that:(1) The relationship between treatment parameters(concentration of electrolyte, voltage,treatment time, temperature of electrolyte and coatings thickness are nonlinear.(2) The coating is made up of MgF2and MgO mainly and the maximum thickness of compact coating is30μm.The relationship between coating’s corrosion resistance and compact coating’s thickness is linear,that means when thickness is30μm, coating is uniform,compact and had good corrosion resistance.(3) The optimum parameters are1000g/L for concentration of KF,360g/L for concentration of KOH,80V for voltage,40℃for temperature of treatment solution and110s for treatment time.This study successfully prepared compact coating of30μm on the surface of AZ51magnesium alloy within110s by micro-arc oxidation,and polarization curve confirmed that the coating had good corrosion resistance.This study did the basic research for the application of micro-arc oxidation technology on magnesium alloy.