负偏压与磁场对微弧氧化涂层表面结构的影响

Influence of Negative Bias and Magnetic Field on Structure of Microarc Oxidation Coating

为了揭示真空条件下氩离子、氩离子/负偏压、靶材/负偏压三种清洗工艺,以及负偏压与磁场协同作用对微弧氧化(MAO)涂层表面结构、厚度、硬度及粗糙度的影响规律,采用MAO和多弧离子镀技术在镁合金AZ31B表面制备镀层,利用扫描电子显微镜考察镀层的微观形貌;纳米压痕仪、测厚仪、粗糙度仪等手段考察镀层的厚度、硬度以及粗糙度随处理工艺变化的规律。当靶基距离为380 mm时,氩离子清洗的MAO涂层表面无明显变化;氩离子与负偏压协同作用时,MAO涂层表面的突起物随负偏压增加而减少,清洗效果变好;但负偏压超过500 V时,二者协同作用形成深孔而破坏了MAO涂层,失去MAO涂层对镁合金基体的保护作用。当Al靶与负偏压协同清洗时,负偏压超过200 V也致使MAO涂层呈现深孔特征。引入磁场沉积MAO/Al镀层时,由于磁场的磁过滤作用使得镀层表面沉积物分布均匀,无明显大颗粒熔滴。施加负偏压清洗容易破坏MAO涂层的表面结构,其与氩离子协同清洗时不应高于500 V,与铝靶协同清洗时应不高于200 V。与单一的负偏压或磁场沉积镀层相比,二者协同作用能获得致密均匀的厚MAO/Al镀层。

To reveal effects of three cleaning processes(argon ion,argon ion/negative bias and target/negative bias)and the synergy between negative bias and magnetic field on the structure,thickness,hardness,and roughness of micro arc oxidation(MAO)coatings.The MAO coatings were prepared on the surface of magnesium(Mg)alloy AZ31 B by micro arc oxidation(MAO)technology first,and then followed multi-arc ion plating treatment.Furthermore,the scanning electron microscope,nanoindenter,thickness gauge and roughness meter were used to investigate the structures and properties of the coatings.There is no obvious change on the MAO coating cleaned by argon ion when the distance is 380 mm between the target and the substrate.Under the synergistic effect of argon ions and negative bias,the greater the negative bias,the better the cleaning effect is.At the same time,the numbers of the protrusions on the coating are decreased.The surface of the MAO coating can be destroyed to form deep holes when the negative bias voltage exceeds 500 V with the synergistic effect of argon ions,which fail the MAO coating to protect Mg alloy.Moreover,there is also some deep holes when the negative bias exceeds 200 V with the synergistic effect of Al target.The neutral or charged particles with large size can be filtered by controlling the magnetic current,so that the dense MAO/Al coating without obvious large particle droplets are formed.But the cleaning of negative bias tends to damage the surface structure of the MAO coating.Therefore,the value of the negative bias should be lower than 500 V when synergic cleaning with argon ions,and not higher than 200 V when synergic cleaning with aluminum targets.Compared to the single negative bias or magnetic field,by the synergic effect of negative bias and magnetic field is easier to form an MAO/Al coating with dense and uniform structure.