外文翻译--用自由铬预先处理在 AZ91 D 镁合金上电镀 Ni－P层 英文版.pdf

aJiang,inrevised27owingtotheiruniquecharacteristicsofhigherstrengthtoandisthoughttobethesimplestandmosteconomicmethodtofinishsteel,aluminum,copper,plasticsandmanyothernickelhasexhibitedmorepopularityduetoitsexcellentmetalscanbeplated.Therearecurrentlytwogeneralsolutionstotreatingmagnesiumpriortoplatingzincimmersionandconversiontreatmentinafluoridecontainingbath3.ItisnotedthatinmanypreviousreportsontheelectrolessplatingonSurfaceCoatingsTechnology201materials.Anotheradvantageoftheelectrolessdepositionweightratioandagooddampingcapacity.However,theapplicationofmagnesiumalloyshasbeenlimitedduetotheundesirableproperties,includingpoorcorrosionandwearresistance.Thecorrosionofmagnesiumalloysdependsontheirmetallurgyandenvironmentalfactors.Toimprovethepracticalusageofmagnesiumalloys,manyresearchershaveattemptedtodevelopanticorrosiveandhighwearresistancestrategies1–8.Electrolessdepositionisavarietyofchemicaldepositiontechnology,involvingthedepositionofmetalsfromsolutionontosurfaceswithoutapplyinganexternalelectricvoltage9propertiessuchashighhardness,wearandcorrosionresistanceandhasattractedextensiveinterestsfromtheacademeandtheindustry10–14.However,theelectrolessplatingonmagnesiumalloys,hasmanychallengesintheprocessingofplatingandthereislimitedreportsonmagnesiumalloys1,15–18.Themagnesiumalloyisextremelysusceptibletogalvaniccorrosionthatpitseverelyonthemetalresultinginanunattractiveappearanceaswellasdecreasedmechanicalproperties.Themostdifficultpartofplatingmagnesiumisdevelopinganappropriatepretreatmentprocess,onceasuitableundercoatingisinplacemanydesired©2006ElsevierB.V.Allrightsreserved.KeywordsChromiumfreepretreatmentMagnesiumalloyCorrosionresistance1.IntroductionMagnesiumanditsalloysplayanimportantroleinmanyfields,suchasaerospace,electronicsandautomobilefieldstechniqueisthatgoodqualitydepositswithuniformitycanbeobtainedwithoutspecialrequirementsforsubstrategeometriesandcapabilityofdepositingoneitherconductiveornonconductiveparts.Amongtheplatingmetals,electrolessitsstructure,morphology,microhardnessandcorrosionresistance.ThepretreatmentlayeronthesubstratenotonlyreducesthecorrosionofmagnesiumduringNi–Pplatingprocess,butalsoreducesthepotentialdifferencebetweenthematrixandthesecondphase.Thus,aNi–PcoatingwithfineanddensestructurewasobtainedontheAZ91Dmagnesiumalloy,whichshowsbettercorrosionresistancethantheNi–PwithchromiumoxideplusHFaspretreatment.ElectrolessNi–PlayerwithonAZ91DmagnesiumW.X.Zhang,J.G.He,Z.H.KeyLaboratoryofAutomobileMaterialsJilinUniversity,DepartmentofMaterialsScienceandEngineering,Received1July2006acceptedAvailableonlineAbstractAphosphatemanganeseconversionfilmwasproposedasthepretreatmentsubstrate,toreplacethetraditionalchromiumoxideplusHFpretreatment.⁎Correspondingauthor.DepartmentofMaterialsScienceandEngineering,JilinUniversity,Changchun130025,China.Emailaddresslianjsjlu.edu.cnJ.S.Lian.02578972/seefrontmatter©2006ElsevierB.V.Allrightsreserved.doi10.1016/j.surfcoat.2006.09.312chromiumfreepretreatmentalloyQ.Jiang,J.S.Lian⁎MinistryofEducation,Changchun130025,ChinaJilinUniversity,Changchun130025,Chinaform28September2006November2006layerbetweenNi–PcoatingandAZ91DmagnesiumalloyThesubsequentNi–Pdepositedonthelayerwasalsocharacterizedby20074594–4600www.elsevier.com/locate/surfcoatmagnesiumalloys1,15–18,themagnesiumalloywasetchedinasolutionofchromiumoxideandnitricacidandsoakedinHFsolutiontoformaconversionfilmbeforeelectrolessplatingNi–P.Nevertheless,metalfinishingindustrieshavetolookforalternativematerialsorspecificallydepositionmethodstoreplacethehexavalentchromiumcompounds,whichareprognickelcoatingfor10min.Aftertakingthefilterpaperaway,redspotsorredareaswerenotedonthesurfaceofthecoating.Theporosityofcoatingwasevaluatedrelativelybytheratioofredspotareatothezoneareapreviouslypastedbythefilterpaper.TheprinciplesofthemethodwerebrieflyexplainedinRef.20.Acidimmersiontest.Thetestin10HClsolutionatroomtemperaturewascarriedoutfordifferentthicknesscoatingsonAZ91Dmagnesiumalloy.Ifthereweremicroporesinthecoatings,thesolutionwoulderodethesubstratethroughthepores.ThentheHinthesolutionwouldbereducedbythemagnesiumandturnedintothehydrogengasbubbles21.Electrochemicalmeasurements.ThepolarizationcurvesofNi–PdepositswereperformedonanElectrochemicalAnalyzerCHI800,Shanghai,ChinabyLinearSweepVoltammetrytechniqueatroomtemperatureina3wt.NaClaqueoussolutionusingaclassicthreeelectrodecell.Theworkingelectrodewascleanedinacetoneagitatedultrasonicallyfor10minbeforetesting.ThecoatedsamplesweremaskedwithepoxyresinEP651sothatonly1cm2areaW.X.Zhangetal./SurfaceCoatingsressivelyrestrictedduetotheirhightoxicityonenvironment19andHFalsoexhibitsstrongcorrosivethatcannotbeeasilycontrolled.Thus,theenvironmentalandhealthfriendlytechnologyhavebeenextensivelystudiedtoeffectivelyinhibitthemagnesiumcorrosionrecently4–7.Moreover,thenickelionswereprovidedbybasicnickelcarbonateinmostNi–Pplatingbathformagnesiumalloy.Inourpreviousstudy,anelectrolessNi–PdepositionontheAZ91Dmagnesiumalloywasproposed18fromaplatingbathcontainingsulfatenickelafterthealloywaspickledinaacidsolutionofchromiumoxideandactivatedinHFsolutiontoformaMgF2film.Inthepresentwork,achromiumfreesolutionpretreatmentCHFPtechnologyonAZ91Dmagnesiumalloyisinvestigated.ThensubsequentNi–Pplatingisrealizedintheplatingbathwherethenickelionsareprovidedbysulfatenickel18.Thedepositwascharacterizedbyitsstructure,morphology,corrosioncharacteristicsandmicrohardness.Forcomparison,theNi–PalloyplatingonthemagnesiumalloysubstratewiththepretreatmentinhexavalentchromiumsolutionandHFsolutionCHHFPwasalsoprovided.2.ExperimentalproceduresThesubstratewasAZ91Ddiecastmagnesiumalloywithasizeof30mm30mm3mm.ThechemicalcompositionofthealloywasgiveninTable1.ThesubstratewasgroundwithNo.2000SiCpaperbeforeCHFPprocesses.Aftergrinding,thesubstratewascleanedinalkalinetoremovesoilsorgreasesonthesurfaceofmagnesiumalloyandrinsedthoroughlyindeionizedwatertoremoveallthealkali.Thenthemagnesiumalloysamplewasimmersedinthepretreatmentbathfor2min,whereH3PO4andMnH2PO42werethemainingredients.Afterbeingrinsedindistilledwater,thesamplewasimmersedintheelectrolesssolutionforplatingNi–Pdepositionlayer.Theelectrolesssolutionwastakenina1000mlglassbeaker,whichwaskeptatconstanttemperaturebyathermostat.ThebathcompositionandalloperationparametersforthepretreatmentandelectrolessNi–PdepositionarelistedinTable2.SurfacemorphologieswereobservedbySEMJSM5310,JapanElectronics.TheattachedEDSINC250wasusedforqualitativeelementalanalysisofthecoating.ThestructureswerestudiedbytheXraydiffractometerXRD,RigakuDymax,JapanwithaCuKαradiationγ0.154178nmandamonochromatorat50kVand300mAwiththescanningrateandstepbeing4°/minand0.02°,respectively.TheharnessesofthemagnesiumalloybeforeandafterelectrolessdepositionwereevaluatedusingaHXD1000microhardnesstesterwithVickersindenter,employingaloadof200gfor15s.ThethicknessofTable1ThecompositionsoftheAZ91Dmagnesiumalloyinwt.AlZnMnNiFeCuCaSiKMg8.770.740.180.0010.0010.001b0.01b0.01b0.01BalanceNi–PdepositionwasmeasuredbythecrosssectionofeachdepositatdifferentintervalsusingSEM.CorrosionresistancetestsweremeasuredunderthefollowingconditionsPorositytest.ThetestwasproposedtoevaluatetheporosityoftheNi–PcoatingonmagnesiumalloyconsideringthatthedepositioncoatingofelectrolessNi–Pisgenerallynotverydense,whicharemicroholesorgapsbetweenthemicrometerclusterswhichareconsistedofamorphousornanocrystallinegrains20.Thatis,afilterpaperarea1cm2wassoakedinareagentsolutionof10g/lNaCl,106g/lethanoland0.1g/lphenolphthaleindissolvedindistilledwater.ThefilterpaperwasthenpastedontotheTable2CompositionandoperatingconditionsoftheNi–PplatingonAZ91DmagnesiumalloythesampleswerecleanedthoroughlywithdeionizedwaterasquicklyaspossiblebetweenanytwostepsofthetreatmentsProcessOperationPlatingbathcompositiong/lCondition1GrindingNo.2000SiCsandpaper2AlkalinecleaningNaOH4565°CNa3PO412H2O1020minMnH2PO420.5H3PO485V/V15mlRoomtemperature3PretreatmentC2H4O220ml1–3minCH3CH2OH50mlHNO380V/V5ml4ElectrolessNi–PNiSO46H2O1NaH2PO2H2O14NaC2H3O213pH6.4±0.2HF40V/V12ml/lTemperature82±2°CNH4HF28Stabilizer0.0014595Technology20120074594–4600wasexposedtotheelectrolyte.Sampleswerealsodegreasedwithacetone,rinsedindeionizedwaterbeforeelectrochemicaltest.Beforethedynamicpotentialsweepexperiments,thesampleswereimmersedintoelectrolyteforabout20mintostabilizetheopencircuitpotentialOCPE0.Thescanningratewas50mVmin−1forallmeasurements.TafelplotwastransformedfromtherecordeddataandthecorrosioncurrentdensityicorrwasdeterminedbyextrapolatingthestraightlinesectionoftheanodicandcathodicTafellines.3.Resultsanddiscussion3.1.CompositionsandmorphologyofthecoatingsSincemagnesiumisoneofthemostelectrochemicallyactivemetal,whencontactswithairorwater,anoxideandhydroxidelayerformsquicklyonthesurface3,whichhaveadetrimentaleffectoncoatingadhesionanduniformity.Thequasipassivefilmonmagnesiumismuchlessstablethantheusualpassivefilms,whichformonmetalssuchasaluminumandstainlesssteels.Thisfilmprovidesonlypoorpittingresistanceformagnesium.Meanwhile,theAZ91DalloyconsistedofprimaryαMggrainssurroundedbyaeutecticmixtureofαandβMg17Al121.Thereisinternalgalvaniccorrosioncausedbythesecondphasesorimpurities.Theβphaseprecipitatedalongthegrainboundaries,whichexhibitedhighercathodicreactionactivityandlowercorrosioncurrentdensitythanthatofα22.Therefore,asuitablepretreatmentisverynecessarytoinsurethatduringthesuccessiveelectrolessdepositionthedepositionrateofmetalionsismuchhigherthanthecorrosionrateofmagnesium,especiallyintheacidicplatingbath18.Onceasuitablebasecoatingisinplacemanydesiredmetalscanbeplatedonmagnesiumalloy.TheXRDpatternstakenontheAZ91Dmagnesiumalloysubstrate,theCHFPsurfaceandtheelectrolessNi–PdepositionFig.1.TheXRDpatternsoftheelectrolessNi–PdepositionontheAZ91DmagnesiumalloyatdifferentintervalsaAZ91Dmagnesiumalloysubstrate,bthesubstrateafterpretreatment2min,andctheelectrolessplatingonthepretreatmentlayerafter1h▪Ni,▾Mg,Mg17Al12.4596W.X.Zhangetal./SurfaceCoatingsTechnology20120074594–4600Fig.2.SEMimagesoftheAZ91Dmagnesiumalloysubstratesurfaceaandthepretreatmentthepretreatmentsurfaceb.Scanningalongthelinelabeledinthefigures.2minsurfaceb.Qualitativechemicalanalysisofthesubstrateaandwhicharethetraceelementsandcouldbeignored.Therefore,phosphorusandmanganeseelementsadheredtothesubstrateduringtheCHFP.Fig.2canddisthelinescreeningofelementanalysistakenalongthelinesmarkedonFig.2aandb,correspondingly.FromFig.2c,itcanbeseenthateachelementuniformlydistributedonthemagnesiumalloysubstratefromthescanningline.TheincreaseofAlanddecreaseofMgspectraFig.2donthewhitephaseFig.2bpositionindicatethatthewhitephasesonFig.2bshouldbeβphase.MuchmoreβphaseswererevealedafterCHFP,whichisconsistentwiththeXRDpatternofFig.1b.4597W.X.Zhangetal./SurfaceCoatingsTechnology20120074594–4600ontheAZ91DmagnesiumalloyareshowninFig.1a,bandc,respectively.ComparedFig.1awithb,itisnoticedthattheβMg17Al12phasebecamedistinguishedonthesurfaceafterCHFP.Thecompositionofthepretreatmentlayerisnotdetected,whosethicknessmaybeunderthelimitoftheinstrument.ThediffractionpatternsoftheasplatedelectrolessNi–PdepositsshowninFig.1chadonlyasingleverybroadpeakat2θ44.88°andthereflectionscorrespondingtothe111planeofafacecenteredcubicfccphaseofnickelcouldbeobserved,whichconsistedwiththephosphoruscontents5.6wt.analyzedbyEDS.ThispatternindicatesthatthestructureoftheasdepositedNi–Pcoatingwasamixtureofamorphousandnanocrystallinenickel23.AlthoughthephasesinthepretreatmentlayercannotbedetectedbyXRD,thepalecoloredsurfacemayimplythepresenceofpassivefilmonthesubstance.ThesurfacemorFig.3.PolarizationcurvesofAZ91Dmagnesiumalloysubstrateandthesubstratewithdifferentlayersina3wt.NaClaqueoussolution.aThemagnesiumalloysubstrate,bsubstratewiththeCHFP,csubstratewiththeNi–PlayerdepositedonCHHFPlayer,dsubstratewiththeNi–PlayerdepositedonCHFPlayer.phologiesoftheAZ91DmagnesiumalloysubstrateandthepretreatmentlayerwereobservedusingSEM,showninFig.2aandb,respectively.Athinfilmcanbeclearlyshownonthepretreatmentsurface.ElementsurfacescreeninganalysisomittedfigureonthesetwosurfacesshowedthatthatbesidesMg,AlandZn,phosphorusandmanganeseelementsexistonthepretreatmentsurfacetheirconcentrationsinthelayeranalyzedbyEDSwere0.84and0.11wt.,respectively.Whileasforsubstrate,thecontentswere0.07and0.02wt.,respectively,Table3CorrosionpotentialandcorrosioncurrentdensityvaluesobtainedfromtheelectrochemicalpolarizationcurvesSamplesCorrosionpotentialvs.Ag/AgCl,Ecorr/VCorrosioncurrentdensity,icorr/μAcm−2aSubstrate−1.502411.8bSubstratewiththeCHFPlayer−1.44248.91cSubstratewiththeNi–PlayeronCHHFPlayer−0.78117.79dSubstratewiththeNi–PlayeronCHFPlayer−0.59915.98Fig.4.SEMimagesoftheelectrolessNi–Pcoatingafter1honAZ91Dmagnesiumalloysurfacea,itscorrespondingcrosssectionbandqualitativechemicalanalysesc,scanningfromthecoatingsurfacetothesubstratealongthelinelabeledinthefigure.