镁合金表面超声滚压预处理对微弧氧化膜耐蚀性能的影响

Effect of Ultrasonic Rolling Pretreatment on Corrosion Resistance of Micro-arc Oxidation Coating of Mg-alloy

镁合金基体首先进行超声滚压预处理后再进行微弧氧化镀膜,结合OM、SEM、EDS、XRD与电化学工作站(模拟体液PBS)对有无超声滚压处理的微弧氧化膜层性能进行测试分析,研究超声滚压处理对镁合金微弧氧化膜层性能的影响。结果表明:超声滚压处理后镁基体表面粗糙度降低、晶粒细化且硬度提升;与镁合金直接微弧氧化的膜层相比,超声滚压预处理之后再进行微弧氧化,膜层中的Si、P、Ca含量比例增大,膜层表面更为致密、光滑,大孔数量明显降低,表面孔隙率由31.7%降低至19.1%;从电化学测试结果看出,与直接微弧氧化的膜层相比超声滚压预处理后膜层的自腐蚀电位高出107 mV,腐蚀电流密度低了一个数量级,并且阻抗性能更优,镁合金超声滚压预处理可有效提升微弧氧化膜层在PBS溶液中的耐蚀性。

Though Mg-alloy can be used as a new generation of implant materials with good biocompatibility and biodegradability,its corrosion rate should be reduced to an acceptable level for the application.For that,at the present,the most commonly measure is to apply a micro-arc oxidation coating on the alloy.However,the porosity of the micro-arc oxidation coating is too large,thereby corrosive species can easy migrate inward through the micro-pores,thus degrade its protective effect.Recently,some scholars have found that pretreatment of the metal matrix can increase the density of the micro-arc oxidation coating.So in this study,Mg-alloy was pretreated by ultrasonic rolling before the micro-arc oxidation.Then the prepared micro-arc oxide ceramic coatings on Mg-alloy with or without ultrasonic rolling treatment were comparatively assessed by means of OM,SEM,EDS,XRD,electrochemical workstation(simulated humoral PBS),to reveal the effect of ultrasonic rolling treatment on the properties of micro-arc oxide ceramic coating.Results show that:after ultrasonic rolling treatment,the treated Mg-alloy matrix presents lower surface roughness,finer grains and higher hardness.In comparison with the Micro-arc oxidation ceramic coating on the un-treated Mg-alloy,the element content of Si,P and Ca is increased in the coating on the pre-treated ones,correspondingly the surface was denser and smoother,and the number of macropores significantly decreased,namely,the surface porosity reduced from 31.7%to 19.1%.From electrochemical tests we can see that,the free corrosion potential was 107 mV higher,the corrosion current density was an order of magnitude lower,and the impedance is much higher for the micro-arc oxidation ceramic coating on Mg-alloy pre-treated by ultrasonic rolling.In conclusion,the pre-ultrasonic rolling treatment could effectively improve the corrosion resistance in PBS solution of the micro-arc oxidation ceramic coatings on Mg-alloy.