Study On The Sealing Treatment Of Mg Alloy Micro-arc Oxidation

In recent years, micro-arc oxidation (MAO) technique is the most favorable method in the surface treatment of magnesium alloys. With the treatment, the wear resistance, corrosion resistance, mechanical strength, and electrical insulation of the metals and their alloys can be effectively improved. Because there exist microcosmic discharge channels in the MAO ceramic coatings, through which corrosion medium can reach Mg alloys, it is very necessary to perform sealing treatment to the MAO ceramic coatings. Electrophoresis, because of the uniqueness of this technique, can be employed to do the job efficiently.In present work, with surface appearance, roughness and thickness of MAO ceramic coatings taken into account, a series of marinate tests on corrosion resistance of the coatings have been carried out for AM60 Mg alloys in silicate electrolyte with and without the coatings, respectively, and further with and without the coating taken the electrophoresis seal treatment, respectively. Meanwhile organic seal treatment is also used just for compassion of the effectiveness of electrophoresis seal treatment on corrosion resistance. Experimental results are analyzed in virtue of electrochemical I/E Polarization curve and it is shown that corrosion resistance is evidently improved for magnesium alloys with micro-arc oxidation ceramic coatings. It is found that 10 microns is the most favorable thickness of coatings under which corrosion rate is the lowest. Furthermore, ceramic layer's porosity shows an advantageous property of firm accretion of sealing onto MAO ceramic coatings.Voltage, temperature, time and distance of electrode are among the key factors of the electrophoresis technique on improving corrosion resistance and other properties of the electrophoresis film. Tests have shown that the best controlling parameters for magnesium alloys with MAO ceramic coating to take the electrophoresis sealing treatment are: voltage 140V, temperature 28°C, distance of electrode 70mm, ratio of electrode 4:1 and duration 2.5 minutes. Moreover, the surface roughness of MAO coatings has a clear influence on the roughness of the electrophoresis film. It is shown that the electrophoresis sealing treatment is the best technique when compared with other organic sealing treatments, with which the corrosion rate will otherwise be remarkably 2 order higher. Therefore electrophoresis is one of the best techniques for sealing treatment for Mg alloys with MAO ceramic coatings.