| Microarc oxidation (MAO) is an advanced coating process for forming ceramic oxide layer on a conductive anodic metal substrate, such as Al, Mg, Ti etc. The ceramic film formed by MAO has many unique advantages, such as good ware resistance, high thermal resistance. So this technology has arosed more and more scholars' interesting, having great commercial potential. Power supply is a key equipment of MAO process. Successfully, XYMAO15 special power supply was developed in laboratory. This power supply can discharge 0～500V unipolar changeable pulse which frequency also can be regulated from 0 to 999Hz. This power supply had satisfied the researched experiment work about MAO.Chapter 2 and 3 of this paper discuss the design process of XYMA015 special power supply. This power supply combined by voltage-regulate circuit and chopper circuit, which are the most important parts. The voltage-regulate circuit control output voltage by regulating the dutyfactor of switch driving signal. The chopper circuit controls the output pulse by regulating the dutyfactor and the frequency of switch driving signal. Based on Intel 80C196KC, the control system of power supply is designed, which including singlechip system circuit, interface circuit, keyboard and display circuit. The control system use PWM as drive signal for voltage-regulate circuit and HSO as drive signal for chopper circuit. Besides, the protect circuit of power supply and Electronic-Counter-Measures are also discussed.Using the power supply, Ceramic coating were fabricated by micro-arc oxidation method with a control mode of constant-current-earlier-constant-voltage-later on 2090 Al-Li alloy and 2090+Ce Al-Li alloy in an electrolytic solution containing NaOH and Na2SiO3. Chapter 4 and 5 discuss about the MAO experiment and results analyzing. The thickness of the MAO film is about 50μm under 900Hz pulse treatment for 60min. The coating grows linearly and more rapidly under higher frequency DC pulse. Scanning by SEM, the photos show that 2090 Al-Li alloy ceramic coating is combined well to the Al substrate, which is composed of two-layer structure with surface loose zone and compact zone. This state is better than 2090+Ce Al-Li alloy ceramic coating. Besides, element distribution is also analyses in ceramic coating. |
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