【作者】 张亚磊；

【导师】 陈砺；

【作者基本信息】 华南理工大学 ， 化学工艺， 2012， 硕士

【摘要】 等离子体电解氧化（PEO）是轻金属材料表面改性的新技术，利用该技术制得的膜层兼具阳极氧化膜及陶瓷膜的性能。目前国内外对于PEO膜层性能做了大量的研究工作，但PEO技术因其高能低效问题而难以得到大规模应用。鉴于此，本论文以AZ31Mg为工作电极，围绕介质阻挡层对击穿放电过程和能耗、气体鞘层形成、陶瓷膜性能的影响以及溶剂组成对溶剂蒸发过程、放电过程能耗、陶瓷膜层性能的影响等方面对等离子体电解氧化过程展开研究。（1）分析了化学转化工艺条件对转化膜厚度、孔隙率、耐蚀性及相组成的影响。转化时间在30min以内，转化膜厚度与转化时间呈线性关系，其线性函数为：d=0.43t-0.44（R²=0.999）；转化时间增加，转化膜更致密，膜层表面更完整；转化膜对镁合金表面的耐腐蚀性能有一定的提高；转化膜主要有MgO及MgAl₂O₄两相组成，转化时间主要影响膜层中两相的含量。（2）通过在试件表面预处理的介质阻挡层减少阳极氧化阶段对PEO过程的影响，分析介质阻挡层对击穿放电过程和能耗、气体鞘层形成、陶瓷膜性能的影响。实验结果表明预处理的介质阻挡层对PEO过程有明显影响：介质阻挡层厚度对PEO过程的电流密度下降快慢、进入稳定放电阶段的时间以及平衡电流密度的大小都有影响；PEO陶瓷膜的生长速度增加近一倍；陶瓷膜中镁橄榄石（Mg₂SiO₄）相的含量显著增加，使陶瓷膜的附着强度、耐摩擦性能及耐腐蚀性能有较大提高； PEO反应过程的能耗显著降低，且在介质阻挡层厚度为8.2μm时最低。（3）结合介质阻挡层作用，分析溶剂中甲醇对PEO过程中气体鞘层形成过程的影响，讨论甲醇对PEO过程放电特性、过程能耗、陶瓷膜性能的影响：甲醇浓度影响PEO过程电流下降的难易及平衡电流密度的大小；甲醇使PEO过程能耗降低，且甲醇浓度在其体积分数为16%时过程的能耗最低；甲醇浓度对PEO陶瓷膜的厚度、附着强度、耐摩擦性能、耐腐蚀性能及膜层相组成无显著影响。（4）结合介质阻挡层和甲醇对等离子体电解氧化过程的影响，简单分析PEO过程的传质传热作用机理以及介质阻挡层在PEO过程中的作用机理。研究表明：介质阻挡层主要是借助于其自身良好的电绝缘性能影响等离子体电解氧化过程初始阶段的电能分布、避免电极与电解液直接接触，减少溶剂电解，使形成气体鞘层的气相主要源于溶剂蒸发过程，降低等离子体电解氧化过程的能量消耗；预处理的介质阻挡层通过改变陶瓷膜的晶相组成分布和相态分布而影响膜层性能；在预处理介质阻挡层高效聚集电能的作用下，甲醇因其本身较小的蒸发焓和比水小的电解能减少气体鞘层形成过程的能量消耗；甲醇改变了电解液的溶剂组成，通过影响反应的热力学环境对等离子体电解氧化过程的放电点产生影响。更多还原

【Abstract】 Plasma electrolyte oxidation （PEO） technology provides a new platform for surfacemodification of light-metallic materials. The films formed by PEO combine the performanceof both anodic oxide films and ceramic films, which broadens the application field oflight-metallic materials. Many researches related to the PEO films’ properties have been downat home and abroad. Because of its high energy inefficient PEO technology cannot be usedwidely. Based on this, the AZ31Mg alloy was used as the working electrode. The influence ofthe dielectric barrier layer’s （DBL） characteristics and solvent composition on the breakdowndischarge, process energy consumption, the gas envelops and performance of the PEOcoatings were investigated.（1） Analyzed the influence of chemical conversion process conditions on conversionfilms’ thickness, porosity, corrosion resistance and the phase composition. The result showthat: The thickness of conversion coating approximates linear growth with conversion time in30minutes, its linear function is d=0.43t-0.44（R2=0.999）; compactness of conversioncoating improves with the extension of conversion time; conversion film can help improvecorrosion resistant performance of the magnesium alloy to some extent; the crystal phase ofconversion film mainly includes MgO and MgAl₂O₄, conversion time has great influence oncomposition of crystal phase.（2） In order to reduce the adverse effects of anodic oxidation during PEO process, thedielectric barrier layer was prepared through chemical conversion pretreatment. The effect ofdielectric barrier layer on the breakdown discharge, process energy consumption, the gasenvelops and performances of the PEO films were investigated. The experimental resultsshow that the pretreated DBL has significant effect: The thickness of DBL has remarkableinfluence on current density, balanced current and stationary discharge of PEO process; thegrowth rate of ceramic membrane doubled; adhesive strength, abrasion resistance andcorrosion resistance of ceramic membrane improve obviously because of MgAl2O4increased;energy consumption of PEO process decreases greatly, it bottoms out lowest when thethickness of conversion film is8.3μm. （3） The effect of methanol on the gas enveloping process was analyzed. The influence ofmethanol concentration on discharge characteristic, process energy consumption, and the PEOfilms’ performance were discussed. The experimental data shows that: the concentration ofmethanol has great impact on current density and balanced current of PEO process; the energyconsumption of PEO process has the very big relations with methanol concentration, when theconcentration of methanol is16%（volume fraction）, energy consumption is lowest; thickness,adhesive strength, abrasion resistance and corrosion resistance of ceramic membrane almosthas nothing to do with methanol concentration.（4） According to the study shows that （1） and （2）, the mechanisms of PEO process’smass and heat transfer as well as DBL’s mechanism of action were analyzed.（5） The results indicated that:1) DBL mainly impacts the electric power distribution ofthe initial stage of PEO process by its good dielectric properties, so that the gas phase mainlycomes from solvent evaporation process other than electrolysis of solvent. By this, the energyconsumption of the reaction was reduced.2) The DBL changed the crystal phase compositionand morphology distribution of PEO films to influence their performance.3) Because of itssmaller evaporation enthalpy and electrolytic energy consumption than water, methanol canmake energy consumption of the gas envelope’s formation process reduced.4) The methanoladded to the solution affects discharge points through changing thermodynamics environmentof PEO reaction.更多还原