| Abstract:Magnesium alloy not only had a lower specific gravity, higher specific strength, higher specific stiffness and good thermal conductivity performance characteristics, but also had good damping, electromagnetic shielding performance and good casting, which had make the magnesium alloy become the best choice for modern automobile, electronics and telecommunications industries and so on. However, compared with other materials, magnesium alloys also had significant deficiencies:low elastic modulus, poor low-temperature toughness, poor creep resistance and high-temperature strength and so on. Especially high chemical activity which restricted the application of magnesium alloy’s performance advantages as the bad corrosion resistance. Therefore, before the practical application, magnesium alloy must be treated by a surface protective treatment. In recent years, the High Velocity Oxy-Fuel (HVOF) technology and Micro-arc Oxidation (MAO) technology which had become two effective surface treatment methods for many materials were two effective surface treatment technologies. Therefore, we had studied the increased anti-corrosion property of the Mg alloy by HVOF and MAO technology.In order to discuss the effect of spray distance on during HVOF spray process and the effects of electrical parameters and additives during MAO process, the properties of aluminum coatings by HVOF at different spray distance and the structure and properties of MAO films by MAO at different current densities, working voltage, frequency, duty cycle and different additive were investigated. And also thermal spray/micro-arc oxidation composite Mg-alloy/Alsprayed/Al2O3composite films were prepared on magnesium alloys. The results showed that as the spraying distance was175mm, the properties of the Al coatings were best. The thickness and adhesion strength were417μm and38MPa, respectively. As for the micro-arc oxidation treatment, the roughness of MAO film was2.52μm when the current density, frequency and duty cycle were4A/dm2, 500Hz and50%respectively. The thickness of the MAO film could reach24μm as the voltage was450V. Added8g/L fluoride in the electrolyte solution could increase the thickness of MAO film from6.5μm to17μm. The MAO film would become more density without decreasing the thickness as the citrate was additive. And the surface roughness would increase to0.48μm when add4g/L phosphate. At last the density of the MAO film whose surface roughness was1.69μm could be improved by the composite technology with thermal spraying/micro-arc oxidation, but the thickness decreased.The corrosion resistance of MAO films and Mg-alloy/Alsprayed/Al2O3composite films was also studied. When the frequency, current density and duty cycle were100Hz,2A/dm2and50%, the corrosion resistance of the MAO film was the best, which could still acquire9th grade after500hours NSST. When the fluoride and citrate were added8g/L and4g/L, the corrosion resistance of MAO film could still acquire9th grade after500hours NSST which was the best. Prepared by HVOF thermal spraying/micro-arc oxidation Mg-alloy/Alsprayed/Al2O3composite films had better corrosion resistance than a single magnesium alloy by micro-arc oxidation treatment, which was corroded until500h in the NSST. |
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