【作者】 李泽；

【导师】 马跃洲；

【作者基本信息】 兰州理工大学 ， 材料加工工程， 2009， 硕士

【摘要】 微弧氧化是在阳极氧化工艺的基础上发展起来一种表面改性新技术，它利用微区电弧放电在金属表面生成陶瓷状氧化膜。本文根据微弧氧化处理过程中的工艺要求和现象，以自行研制的多功能脉冲微弧氧化电源为试验平台，通过对膜层生长过程的探讨了镁合金微弧氧化膜层形成机理，提出微区电弧放电模型；根据对系统负载特性的分析提出微弧氧化对电源的要求，并据此设计了一种新型的带放电回路的微弧氧化脉冲电源。研究表明，微弧氧化过程主要分为阳极氧化、微弧放电、大弧放电三个阶段。微弧氧化膜层是由一系列离散的微区电弧放电产生的金属氧化物累积形成，瞬间完成的微小区域内的电弧放电，使生成的氧化物经历骤热骤冷过程，从而可获得非平衡组织结构的金属氧化物膜层。微区电弧放电主要分为电解、放电、氧化、冷却等四个过程。其产生电弧放电的必要条件是：试样表面存在氧气气泡并承受强电场。微弧氧化成膜主要包括电解液、初始膜层、导电通道、高压电场及水的电解产生氧气等五个条件。通过对微弧氧化系统电压、电流信号的采集和分析发现负载阻抗随时间的增加是逐渐增加的，并用MATLAB拟合出在频率700、占空比20％时的系统阻抗与处理时间的关系式。研究发现，微弧氧化过程中负载特性可以用RC电路来简单等效，并求出了膜层厚度与工艺参数之间的对应公式。分别采用直流电压、单极性脉冲、双极性脉冲、带放电回路的电源形式分别进行微弧氧化实验，发现电源形式对镁合金微弧氧化过程起着关键性的作用。带放电回路的脉冲形式能极大抑制微弧氧化的大弧倾向，因此具有较好的处理效果。研究了恒定电压、电流下微弧氧化陶瓷膜的生长速率，发现在在恒流模式下膜层生长效率较高。探求脉冲作用时间与冷却时间之间的关系，发现在频率700Hz时两者的最佳配比是1：4。根据负载特性研究表明，阻性和容性是微弧氧化负载的主要特点，放电回路的引入能解决其电容性在微弧氧化过程中造成电弧持续燃烧的问题。据此设计了一种新型的带放电回路的微弧氧化脉冲电源。电源使用IGBT串联实现脉冲放电间隙放电回路、IGBT并联实现电源的大功率输出；控制系统以80C196KB单片机为核心，利用其高速输入口进行同步信号采集和高速输出口产生IGBT驱动信号；用数字PI调节方式获得恒流、恒压输出特性。研制的样机在运行中表现出良好的稳定性和可靠性。更多还原

【Abstract】 Micro-Arc Oxidation is a new surface treatment technique,developed from anodic oxidation,which used micro-arc discharge in the metal oxide ceramic membrane.In this paper,we discuss mechanism of micro-discharge and model of micro-arc oxidation, which based on the test platform which build with self-developed high-power, multi-output of the pulse;the techniques requirement and phenomenon and the grown progress of ceramic membrane.Design a new typical power according as the requirement which bring forward based on system load characteristic.Study showed Micro-arc oxidation process can be divided into three stages,named: anodic oxidation,the spark discharge and the micro-arc oxidation stages.Ceramic layer was mainly components by metal oxide which formed by a series of micro-discharge.Non-balance metal oxide film can be made by discharge in small extent in the progress of fast hot and then fast cool.Micro-arc discharge can be divided into four stages,named:electrolyte,discharge,oxidation and cooling.The necessary condition of arc-discharge happening is exist of oxygen on the magnesium alloy surface and the oxygen endured definite electric field.Forming Micro-arc Oxidation film must have five conditions,it contains:electrolyte,initialization film,high-handed electric field and the oxygen produced by electrolyze water.According to collect and analyze signals of voltage and current.Found that:the increase of load impedance is gradually along with time.And then educe a curve of system impedance-deal time in the condition of frequency 700 and pulse duty 20%by MATLAB.Study showed that:The load characteristic of Micro-arc Oxidation can be replaced by RC circuit.And then educe a formula which between film thickness and techniques parameter.We can find that the typical of power have a key function in the progress of magnesium alloy Micro-arc Oxidation when we tried different power contain:direct current,AC pulse power,DC pulse power and discharge current pulse power.The discharge current pulse power has a good effect because it can abolish big arc effectually.Find that the film grown fast in the invariableness current modal when we study the film speed between invariableness voltage and invariableness current. The best match time between pulse action and cooling is 1:4 in the condition of pulse frequency 700Hz.The study of load characteristic showed that:the mostly characteristic are resistance and capacitance.The problem of arc persistence burning can be settled by importing the discharge current.According this we design a new typical power with discharge current.This power come true pulse discharge alternation with IGBT in series;come true output great power with IGBT parallel connection.The control system core is 80C196KB which high speed input gob can be used to collect in-phase signal and output high speed IGBT drive signal;invariableness voltage and invariableness current output characteristic can be obtained by figure PI adjusted.The sample power has a good characteristic of credibility in the circulating.更多还原