第二相对镁基材料微弧氧化过程的影响机制

EFFECTS OF SECOND PHASES ON MICROARC OXIDATION PROCESS OF MAGNESIUM BASE MATERIALS

对含有不同类型第二相的镁基材料进行微弧氧化处理,研究基体材料第二相对其微弧氧化行为的影响规律及其影响机制.利用SEM观察第二相在微弧氧化初期阶段的存在状态,并结合EDS分析第二相的成分及状态变化;通过不同镁基材料在微弧氧化过程中的电压演变趋势分析第二相对微弧氧化行为的影响.根据微弧氧化膜的生长原理,将膜层的生长过程简化等效为一个电容器的反复击穿-重构过程,并依此讨论了微弧氧化膜的形成过程及第二相的影响机理.结果表明,第二相对镁基材料微弧氧化行为的影响与其自身特性密切相关;在微弧氧化的初期阶段,第二相是否具备阀金属特性及其导电特性是影响微弧氧化行为的重要因素.对于具备阀金属特性的第二相,由于其表面能够形成火花放电所必须的阻挡层,因此第二相的存在不会对微弧氧化行为产生明显影响.对于不具备阀金属特性的第二相,其导电特性决定了镁基材料在微弧氧化初期阶段能否正常发生火花放电并顺利进入膜层生长阶段.

The effects of second phases on microarc oxidation（MAO,also named plasma electrolytic oxidation-PEO） behavior of Mg base materials were investigated and the related mechanism was discussed.The formation of barrier layer and its influence on sparking discharge behavior were characterized and analyzed on the base of systematic selecting and designing substrate materials.The variation of second phases at the early MAO stage was observed and analyzed by SEM and EDS,and then the effect mechanism of second phases on MAO behaviors was revealed.Voltage evolution trend during MAO were recorded to study the formation state of the barrier layer on the different Mg base materials.According to the growth mechanism of MAO film,the film growth process can be simplistically considered as a repeated breakdown and reconstruction process of a capacitor.Accordingly,the growth process of MAO film on multiphase metal materials and the effects of second phases were discussed.The results show that different second phases in substrate materials have different effects on formation process of MAO films,depending on their own characteristics.For the second phases which have the characteristics of valve metals,although selective sparking discharge occurs at the early stage of MAO,the second phases will not hinder the growth of MAO film since barrier layer can form on the second phases,and they will not induce structural defects into the film-substrate interface.If the second phases have not the characteristics of valve metals,their conductivity property will be an important influencing factor to affect the MAO behaviors.For the elecinsulating second phases which have not the characteristics of valve metals,sparking discharge just occurs on Mg matrix in the substrate,while doesn＇t occur on the second phases;the second phases exist in the MAO film as heterogeneous phases,do not react in MAO process,and will not hinder the growth of MAO film.For the semi-conductive second phases which have not the characteristics of valve metals,they delay the growth of MAO film because they destroy the integrity of barrier layer.For the electroconductive second phases which have not the characteristics of valve metals,they seriously hinder the growth of MAO film.