电参数对镁合金微弧氧化膜层的显微结构和耐蚀性能的影响

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1、华中科技大学硕士学位论文电参数对镁合金微弧氧化膜层的显微结构和耐蚀性能的影响姓名：刘全心申请学位级别：硕士专业：材料加工工程指导教师：蔡启舟20050401华中科技大学硕士学位论文摘要镁合金微弧氧化技术是通过电解液中高压放电作用使镁合金表面形成硬质陶瓷层的一种新工艺所形成的陶瓷膜层具有硬度高绝缘性和耐蚀性好与基体结合力强的优点是一种极具发展前途的镁合金表面处理技术本文利用自主开发的微弧氧化专用电源对置于(NaPO3)6溶液中的AZ91D镁合金进行微弧氧化处理研究了电流电压频率占空比和波形等电参数对膜层的显微结构和耐蚀性能的影响规律试验结果表明微弧氧化处理过程中电压电流呈规律性的变化

2、当电压电流和占空比增大时膜层的增厚速度增大相应地表面粗糙度增大孔隙率也增大而当频率增大时膜层的增厚速度减小表面更光滑孔隙率减小通过微弧氧化形成陶瓷膜层后镁合金的耐蚀性能得到显著改善借助金相显微镜和SEM观察了膜层表面和断面的形貌用能谱仪和XRD研究了膜层的成分组成(NaPO3)6溶液中镁合金微弧氧化膜层由外层疏松层和内层致密层组成内层致密层与基体之间为冶金结合外层疏松层存在许多放电微孔陶瓷膜相组成的主要为MgOMgAl2O4Mg3(PO4)2关键词镁合金微弧氧化电参数显微结构耐蚀性能I华中科技大学硕士学位论文AbstractMicroarcoxidation(MAO)ofmagne

3、siumalloysisaplasmadischargethatoccursatthemetal/electrolyteinterfacewhentheappliedvoltageexceedsacertaincriticalbreakdownvalue.Theprocessproducesthick,hardandwell-adheredceramic-likecoatingstobeobtainedwithhighcorrosionresistance,thermalstabilityanddielectricproperties.Therefore,MAOisoneofthe

4、mostprospectivemethodsofsurfacetreatmentformagnesiumanditsalloys.Inthisinvestigation,theMAOprocessingonmagnesiumalloyAZ91Din(NaPO3)6aqueoussolutionwascarriedoutbyusingofthepowersupplymanufacturedwithourowndesign.Theeffectofpulseparameters(voltageorcurrent,frequencyanddutycycle)onmicrostructure

5、andcorrosionresistancewasinvestigated.Theexperimentalresultsshowthat,thevoltageandcurrentchangeregularly.Thegrowingrateofcoatingsincreaseswiththeelevatingofvoltage,currentanddutycycle.Accordingly,coatingsurfacebecomesrougherandthepercentofporeincreases,aswell.But,whenfrequencyincreases,thegrow

6、ingrateofcoatingsreduces,thesurfacebecomessmootherandthepercentofporedecreases.Theceramic-likecoatingsformedduringMAOprocessingcanenhancethecorrosionresistanceofAZ91Dalloysignificantly.Thecoatingmicrostructureandmorphologywerecharacterizedbyopticalandscanningelectronmicroscopy,observingthestru

7、cturebothparalleltothesubstrateandalsoinpolishedcross-sections.PhasecompositionwasstudiedbyXRDanalysis.Thecoatingsformedin(NaPO3)6aqueoussolutioncontainedtwolayers:anouterlooselayer,whichhasalotofsmallpores,andaninnercompactlayer,whichg