【作者】 潘明强；

【导师】 狄士春；

【作者基本信息】 哈尔滨工业大学 ， 机械制造及其自动化， 2010， 博士

【摘要】 微弧氧化技术具有工艺灵活、操作简单、表面改性效果显著以及工艺过程绿色环保等诸多优点,其工业应用前景十分广阔。随着微弧氧化技术工业化应用的深入,工业应用对膜层表面质量要求越来越高。而表面粗糙度作为表征膜层表面质量的性能指标之一,也越来越受到重视。膜层表面粗度在火花放电生成膜层的过程中同步形成,因此探讨火花放电过程和膜层形成机制是研究膜层表面粗糙度的基础。首先本文根据放电火花变化特征将整个微弧氧化处理过程分成不同的处理阶段,分析不同阶段放电火花特征、膜层表面形貌、电流电压变化规律以及它们之间的关系。在分析单个火花放电过程中,根据单个火花放电产生到消失的时序,将单个火花放电过程分为四个连续的阶段,即火花放电等离子源形成、等离子体放电击穿膜层、构成膜层的物质生成、等离子体放电火花熄灭。利用时序分段法对单个火花放电从形成到消失整个过程的机制进行研究,进一步探讨微弧氧化过程中的火花演化和膜层形成机理。通过对白色火花放电阶段和红色火花放电阶段的宏观反应特点和生成膜层微观形貌特征进行分析,建立白色火花放电和红色火花放电等离子源形成模型。揭示了两个阶段的火花放电等离子体源形成过程。白色火花放电阶段的等离子体源是电子轰击膜层表面包裹的气泡层而形成;而在红色火花放电阶段多次放电后造成金属正电极、溶液等效负电极上的尖端凸起延伸到膜层内部,同膜层中封闭的气孔一起在电场中形成强电场区,当强电场中绝缘介质极化达到极限时就形成了放电等离子源。通过对膜层中不同位置产生等离子源形成放电通道的过程进行分析,建立三种膜层击穿过程火花放电通道模型,利用这三种火花放电通道模型能很好的解释微弧氧化过程中相同时刻放电火花大小不同的现象、膜层生长形成机制以及抑弧氧化的形成机理等微弧氧化问题。利用单个火花放电分析理论可以清楚地阐明火花放电自动产生和消失的机制,以及单向脉冲输出和双向脉冲输出微弧氧化处理过程中火花放电状态在时空上的变化问题。然后通过分析处理铝合金LD10和LY12试验过程中的火花变化状态和膜层形貌,验证利用单个火花放电相关理论分析的膜层生长形成过程和膜层表面形貌形成机制,及火花放电与膜层生长演变之间的关系,其演变过程依次为:绝缘非晶向膜层形成→尖端大火花放电引起相变→大火花转移使膜层整体逐步相变→下一轮尖端放电和膜层生长→膜层生长结束。最后,将支持向量机数据回归分析方法与正交试验设计方法相结合,建立基于正交试验的支持向量机数据回归分析的微弧氧化参数溶液温度、频率、占空比、处理时间与膜层表面粗糙度之间关系的工艺模型,利用工艺模型生成处理铝合金LD10和镁合金AZ91D的工艺参数值。以优化参数为基础进行单因素试验,分析处理方式和基体材料对溶液温度、频率、占空比、处理时间的影响,以及微弧氧化参数对膜层表面粗糙度影响的工艺规律。更多还原

【Abstract】 Micro-arc oxidation with the remarkable effect of surface modification, the environmentaly friendly technology, simple process and easy operation etc., has a very good prospect for industrial applications. With the industrial application development, the quality of coating surface is higher and higher that industrial application requestes. And the surface roughness, one of the indicators that evaluate the coating surface performance, attracts more and more attertion. During micro-arc oxidation processing, the coating surface forms that accompanies the spark discharge genertates the coating. And it is importmant to the surface roughness that spark discharge and coating formation are researched.At first, this paper has summarized the phenomenon such as coating surface morphology, current, voltage in the different spark stages. According to the sequence of a single spark discharge from gengerating to disappearing, a single spark diacharge was divided into four consecutive phases, namely the plasma soruceof the spark discharge formed, coating breakdown, the coating material generated, and the spark disappearing. The mechanism of a single spark discharge process was researched by use of the sub-timing method. Further the mechanism of coating formation and spark discharge variation were explored.According to analysis of the discharge phenomenon and coating microstructure in the stages of white spark and red spark, the mechanism of the plasma source formation is different in two stages. It causes the plasma soruce formation that the electron bombards the bubble wrapping the coating in the white spark stage. And in the red spark stage, the area of strong electric field generates the plasma source where the coating of excessive polarization turns out easily. Focusing on the two mechanism of plasma source formation the two models were established that white and red spark discharge plasma source form.During analysis of the discharge channel formation from plasma source in different locations of coating, three kinds of discharge channel models were obtained. The models successfully explain the phenomenon that the different sizes spark exist in the same moment during micro-arc oxidation process, the mechanism of the coating formation, and the mechanism of suppressing arc oxidation.The theory of a single spark discharge successfully explained the spark discharge mechanism of auto-generating and disappearing, and revealed the spark discharge mechanism of auto-evolution processed by the single-pulse output and double-pulse output.Then, the mechanisms of the coating and the surface topography formation were researched by using the theory of a single spark discharge, and were verified by the experiments performenced on LD10 and LY12. At the same time, the relationship between spark discharge and the evolution of coating formation was obtained, as follow: the coating formation of insulating amorphous→large spark turning out in cutting-edge position and phase change→large spark and phase change moving to specimen center→scan completing and a new round of discharge and coating growth→the end of the coating growth.Finally, the support vector machine regression analysis was introduced for the micro-arc oxidation process data analysis, and combined with the orthogonal experimental design. It is first created the model of the support vector machine regression analysis on orthogonal design basis for micro-arc oxidation process data analysis, and the processing parameters were successfully predict to treat LD10 and AZ91D by the model. In order to analysis influence of the process approach and substrate material on the frequency, duty ratio, time, and working solution temperature, and variation of the coating surface roughness with these parameters, the experiments were performanced according to the predictive parameters.更多还原