溶质离子对AZ31B镁合金微弧诱发过程和陶瓷层结构的影响

Effect of Solute Ions on Plasma Generation Process and Microstructure of Microarc Oxidation Layer on AZ31B Magnesium Alloy

采用微弧氧化方法在AZ31B镁合金表面制备了陶瓷层.研究了AZ31B镁合金微弧氧化溶液体系中KOH和Na2SiO3浓度对微弧等离子体诱发过程和陶瓷层微观结构的影响,通过涡流测厚仪、扫描电子显微镜和X射线衍射仪分析了陶瓷层的物相组成、微观形貌和厚度随KOH和Na2SiO3浓度的变化规律.研究表明：恒流模式下,KOH溶液在AZ31B镁合金表面诱发微弧时存在1个临界浓度,约为27 mmol/L,且随着KOH浓度的增大,对基体和氧化膜的溶解作用加剧,影响微弧等离子体诱发的稳定性.Na2SiO3含量显著影响镁合金表面微弧诱发过程和陶瓷层的微观结构,随着Na2SiO3浓度的增大,陶瓷层生长速率增快,膜层表面由光滑转变为微孔结构,且孔径逐渐增大;Na2 SiO3浓度在1.6～6.4 mmol/L时陶瓷层中主要以MgO为主,Na2Si03浓度大于16 mmol/L时,Mg2 SiO4和非晶相明显增多.

Ceramic coating on AZ31B Mg alloy was fabricated by a microarc oxidation （MAO） method.The effect of Na2 SiO3 and KOH as sodium silicate system solutions on the plasma inducing process and the microstructure of MAO ceramic layer on AZ31B Mg alloy was investigated.The change of phase composition,morphology and thickness of ceramic layer in the presence of KOH and Na2 SiO3 was analyzed by eddy current thickness gauge test,Xray diffraction and scanning electron microscopy,respectively.The results show that there exists a critical concentration of KOH （i.e.,27 mmol/L） to induce plasma.The KOH can dissolve the magnesium base and oxide layer and affect the stability of plasma when the concentration increases.The Na2 SiO3 can affect the plasma inducing process and the microstructure of MAO layer.The growth rate of ceramic layer accelerates,the smooth surface of specimen gradually becomes porous and the pore size increases with increasing the concentration of Na2 SiO3 in KOH solution.The MgO is the main phase in the ceramic layer when the concentration of Na2 SiO3 is 1.6 6.4 mmol/L,and the content of Mg2 SiO4 and the amorphous phase increase when the Na2 SiO3 is ＞ 16 mmol/L.