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,inrevised27owingtotheiruniquecharacteristicsofhigherstrength-to-andisthoughttobethesimplestandmosteconomicmethodtofinishsteel,aluminum,copper,plasticsandmanyothernickelhasexhibitedmorepopularityduetoitsexcellentmetalscanbeplated.Therearecurrentlytwogeneralsolutionstotreatingmagnesiumpriortoplating:zincimmersionandconversiontreatmentinafluoride-containingbath3.ItisnotedthatinmanypreviousreportsontheelectrolessplatingonSurface&CoatingsTechnology201materials.Anotheradvantageoftheelectrolessdepositionweightratioandagooddampingcapacity.However,theapplicationofmagnesiumalloyshasbeenlimitedduetotheundesirableproperties,includingpoorcorrosionandwearresistance.Thecorrosionofmagnesiumalloysdependsontheirmetallurgyandenvironmentalfactors.Toimprovethepracticalusageofmagnesiumalloys,manyresearchershaveattemptedtodevelopanticorrosiveandhighwear-resistancestrategies18.Electrolessdepositionisavarietyofchemicaldepositiontechnology,involvingthedepositionofmetalsfromsolutionontosurfaceswithoutapplyinganexternalelectricvoltage9propertiessuchashighhardness,wearandcorrosionresis-tanceandhasattractedextensiveinterestsfromtheacademeandtheindustry1014.However,theelectrolessplatingonmagnesiumalloys,hasmanychallengesintheprocessingofplatingandthereislimitedreportsonmagnesiumalloys1,1518.Themagnesiumalloyisextremelysusceptibletogalvaniccorrosionthatpitseverelyonthemetalresultinginanunattractiveappearanceaswellasdecreasedmechanicalproperties.Themostdifficultpartofplatingmagnesiumisdevelopinganappropriatepretreatmentprocess,onceasuitableundercoatingisinplacemanydesired©2006ElsevierB.V.Allrightsreserved.Keywords:Chromium-freepretreatment；Magnesiumalloy；Corrosionresistance1.IntroductionMagnesiumanditsalloysplayanimportantroleinmanyfields,suchasaerospace,electronicsandautomobilefieldstechniqueisthatgoodqualitydepositswithuniformitycanbeobtainedwithoutspecialrequirementsforsubstrategeome-triesandcapabilityofdepositingoneitherconductiveornonconductiveparts.Amongtheplatingmetals,electrolessitsstructure,morphology,microhardnessandcorrosion-resistance.ThepretreatmentlayeronthesubstratenotonlyreducesthecorrosionofmagnesiumduringNiPplatingprocess,butalsoreducesthepotentialdifferencebetweenthematrixandthesecondphase.Thus,aNiPcoatingwithfineanddensestructurewasobtainedontheAZ91Dmagnesiumalloy,whichshowsbettercorrosionresistancethantheNiPwithchromiumoxideplusHFaspretreatment.ElectrolessNiPlayerwithonAZ91DmagnesiumW.X.Zhang,J.G.He,Z.H.KeyLaboratoryofAutomobileMaterials(JilinUniversity),DepartmentofMaterialsScienceandEngineering,Received1July2006；acceptedAvailableonlineAbstractAphosphate-manganeseconversionfilmwasproposedasthepretreatmentsubstrate,toreplacethetraditionalchromiumoxideplusHFpretreatment.Correspondingauthor.DepartmentofMaterialsScienceandEngineering,JilinUniversity,Changchun130025,China.E-mailaddress:lianjsjlu.edu.cn(J.S.Lian).0257-8972/$-seefrontmatter©2006ElsevierB.V.Allrightsreserved.doi:10.1016/j.surfcoat.2006.09.312chromium-freepretreatmentalloyQ.Jiang,J.S.LianMinistryofEducation,Changchun130025,ChinaJilinUniversity,Changchun130025,Chinaform28September2006November2006layerbetweenNiPcoatingandAZ91DmagnesiumalloyThesubsequentNiPdepositedonthelayerwasalsocharacterizedby(2007)45944600www.elsevier.com/locate/surfcoatmagnesiumalloys1,1518,themagnesiumalloywasetchedinasolutionofchromiumoxideandnitricacidandsoakedinHFsolutiontoformaconversionfilmbeforeelectrolessplatingNiP.Nevertheless,metalfinishingindustrieshavetolookforalternativematerialsorspecificallydepositionmethodstore-placethehexavalentchromiumcompounds,whichareprog-nickelcoatingfor10min.Aftertakingthefilterpaperaway,redspotsorredareaswerenotedonthesurfaceofthecoating.Theporosityofcoatingwasevaluatedrelativelybytheratioofredspotareatothezoneareapreviouslypastedbythefilterpaper.TheprinciplesofthemethodwerebrieflyexplainedinRef.20.Acidimmersiontest.Thetestin10%HClsolutionatroomtemperaturewascarriedoutfordifferentthicknesscoatingsonAZ91Dmagnesiumalloy.Ifthereweremicroporesinthecoatings,thesolutionwoulderodethesubstratethroughthepores.ThentheH+inthesolutionwouldbereducedbythemagnesiumandturnedintothehydrogengasbubbles21.Electrochemicalmeasurements.ThepolarizationcurvesofNiPdepositswereperformedonanElectrochemicalAna-lyzer(CHI800,Shanghai,China)byLinearSweepVoltam-metrytechniqueatroomtemperatureina3wt.%NaClaqueoussolutionusingaclassicthree-electrodecell.Theworkingelectrodewascleanedinacetoneagitatedultrason-icallyfor10minbeforetesting.Thecoatedsamplesweremaskedwithepoxyresin(EP651)sothatonly1cm2areaW.X.Zhangetal./Surface&Coatingsressivelyrestrictedduetotheirhightoxicityonenvironment19andHFalsoexhibitsstrongcorrosivethatcannotbeeasilycontrolled.Thus,theenvironmentalandhealthfriendlytech-nologyhavebeenextensivelystudiedtoeffectivelyinhibitthemagnesiumcorrosionrecently47.Moreover,thenickelionswereprovidedbybasicnickelcarbonateinmostNiPplatingbathformagnesiumalloy.Inourpreviousstudy,anelectrolessNiPdepositionontheAZ91Dmagnesiumalloywasproposed18fromaplatingbathcontainingsulfatenickelafterthealloywaspickledinaacidsolutionofchromiumoxideandactivatedinHFsolutiontoformaMgF2film.Inthepresentwork,achromium-freesolutionpretreatment(CHFP)technologyonAZ91Dmagnesiumalloyisinvestigat-ed.ThensubsequentNiPplatingisrealizedintheplatingbathwherethenickelionsareprovidedbysulfatenickel18.Thedepositwascharacterizedbyitsstructure,morphology,cor-rosioncharacteristicsandmicrohardness.Forcomparison,theNiPalloyplatingonthemagnesiumalloysubstratewiththepretreatmentinhexavalentchromiumsolutionandHFsolution(CH+HFP)wasalsoprovided.2.ExperimentalproceduresThesubstratewasAZ91Ddiecastmagnesiumalloywithasizeof30mm×30mm×3mm.ThechemicalcompositionofthealloywasgiveninTable1.ThesubstratewasgroundwithNo.2000SiCpaperbeforeCHFPprocesses.Aftergrinding,thesubstratewascleanedinalkalinetoremovesoilsorgreasesonthesurfaceofmagnesiumalloyandrinsedthoroughlyindeionizedwatertoremoveallthealkali.Thenthemagnesiumalloysamplewasimmersedinthepretreatmentbathfor2min,whereH3PO4andMn(H2PO4)2werethemainingredients.Afterbeingrinsedindistilledwater,thesamplewasimmersedintheelectrolesssolutionforplatingNiPdepositionlayer.Theelectrolesssolutionwastakenina1000-mlglassbeaker,whichwaskeptatconstanttemperaturebyathermostat.ThebathcompositionandalloperationparametersforthepretreatmentandelectrolessNiPdepositionarelistedinTable2.SurfacemorphologieswereobservedbySEM(JSM-5310,JapanElectronics).TheattachedEDS(INC250)wasusedforqualitativeelementalanalysisofthecoating.ThestructureswerestudiedbytheX-raydiffractometer(XRD,RigakuDymax,Japan)withaCuKradiation(=0.154178nm)andamono-chromatorat50kVand300mAwiththescanningrateandstepbeing4°/minand0.02°,respectively.TheharnessesofthemagnesiumalloybeforeandafterelectrolessdepositionwereevaluatedusingaHXD-1000microhardnesstesterwithVickersindenter,employingaloadof200gfor15s.ThethicknessofTable1ThecompositionsoftheAZ91Dmagnesiumalloy(inwt.%)AlZnMnNiFeCuCaSiKMg8.770.740.180.0010.0010.001b0.01b0.01b0.01BalanceNiPdepositionwasmeasuredbythecross-sectionofeachdepositatdifferentintervalsusingSEM.Corrosionresistancetestsweremeasuredunderthefollow-ingconditions:Porositytest.ThetestwasproposedtoevaluatetheporosityoftheNiPcoatingonmagnesiumalloyconsideringthatthedepositioncoatingofelectrolessNiPisgenerallynotverydense,whicharemicro-holesorgapsbetweenthemicrometerclusters(whichareconsistedofamorphousornanocrystallinegrains)20.Thatis,afilterpaper(area:1cm2)wassoakedinareagentsolutionof10g/lNaCl,106g/lethanoland0.1g/lphenolphthaleindissolvedindistilledwater.ThefilterpaperwasthenpastedontotheTable2CompositionandoperatingconditionsoftheNiPplatingonAZ91Dmagnesiumalloy(thesampleswerecleanedthoroughlywithdeionizedwaterasquicklyaspossiblebetweenanytwostepsofthetreatments)ProcessOperationPlatingbathcomposition(g/l)Condition1GrindingNo.2000SiCsandpaper2AlkalinecleaningNaOH4565°CNa3PO4·12H2O1020minMn(H2PO4)20.5H3PO4(85%V/V)15mlRoomtemperature3PretreatmentC2H4O220ml13minCH3CH2OH50mlHNO3(80%V/V)5ml4ElectrolessNiPNiSO4·6H2O1NaH2PO2·H2O14NaC2H3O213pH6.4±0.2HF(40%V/V)12ml/lTemperature82±2°CNH4HF28Stabilizer0.0014595Technology201(2007)45944600wasexposedtotheelectrolyte.Sampleswerealsodegreasedwithacetone,rinsedindeionizedwaterbeforeelectrochem-icaltest.Beforethedynamicpotentialsweepexperiments,thesampleswereimmersedintoelectrolyteforabout20mintostabilizetheopen-circuitpotential(OCP)E0.Thescan-ningratewas50mVmin1forallmeasurements.Tafelplotwastransformedfromtherecordeddataandthecorrosioncurrentdensity(icorr)wasdeterminedbyextrapolatingthestraight-linesectionoftheanodicandcathodicTafellines.3.Resultsanddiscussion3.1.CompositionsandmorphologyofthecoatingsSincemagnesiumisoneofthemostelectrochemicallyactivemetal,whencontactswithairorwater,anoxideandhydroxidelayerformsquicklyonthesurface3,whichhaveadetrimentaleffectoncoatingadhesionanduniformity.Thequasi-passivefilmonmagnesiumismuchlessstablethantheusualpassivefilms,whichformonmetalssuchasaluminumandstainlesssteels.Thisfilmprovidesonlypoorpittingresistanceformag-nesium.Meanwhile,theAZ91Dalloyconsistedofprimary-Mggrainssurroundedbyaeutecticmixtureofand-Mg17Al121.Thereisinternalgalvaniccorrosioncausedbythesecondphasesorimpurities.The-phaseprecipitatedalongthegrainboundaries,whichexhibitedhighercathodicreactionactivityandlowercorrosioncurrentdensitythanthatof22.Therefore,asuitablepretreatmentisverynecessarytoinsurethatduringthesuccessiveelectrolessdepositionthedepositionrateofmetalionsismuchhigherthanthecorrosionrateofmagnesium,especiallyintheacidicplatingbath18.Onceasuitablebasecoatingisinplacemanydesiredmetalscanbeplatedonmagnesiumalloy.TheXRDpatternstakenontheAZ91Dmagnesiumalloysubstrate,theCHFPsurfaceandtheelectrolessNiPdepositionFig.1.TheXRDpatternsoftheelectrolessNiPdepositionontheAZ91Dmagnesiumalloyatdifferentintervals:(a)AZ91Dmagnesiumalloysubstrate,(b)thesubstrateafterpretreatment2min,and(c)theelectrolessplatingonthepretreatmentlayerafter1h(Ni,Mg,Mg17Al12).4596W.X.Zhangetal./Surface&CoatingsTechnology201(2007)45944600Fig.2.SEMimagesoftheAZ91Dmagnesiumalloysubstratesurface(a)andthepretreatmentthepretreatmentsurface(b).Scanningalongthelinelabeledinthefigures.2minsurface(b).Qualitativechemicalanalysisofthesubstrate(a)andwhicharethetraceelementsandcouldbeignored.Therefore,phosphorusandmanganeseelementsadheredtothesubstrateduringtheCHFP.Fig.2(c)and(d)isthelinescreeningofelementanalysistakenalongthelinesmarkedonFig.2(a)and(b),correspondingly.FromFig.2(c),itcanbeseenthateachelementuniformlydistributedonthemagnesiumalloysubstratefromthescanningline.TheincreaseofAlanddecreaseofMgspectra(Fig.2(d)onthewhitephase(Fig.2(b)positionindicatethatthewhitephasesonFig.2(b)shouldbephase.MuchmorephaseswererevealedafterCHFP,whichisconsistentwiththeXRDpatternofFig.1(b).4597W.X.Zhangetal./Surface&CoatingsTechnology201(2007)45944600ontheAZ91DmagnesiumalloyareshowninFig.1(a),(b)and(c),respectively.ComparedFig.1(a)with(b),itisnoticedthatthe-Mg17Al12phasebecamedistinguishedonthesurfaceafterCHFP.Thecompositionofthepretreatmentlayerisnotde-tected,whosethicknessmaybeunderthelimitoftheinstru-ment.Thediffractionpatternsoftheas-platedelectrolessNiPdepositsshowninFig.1(c)hadonlyasingleverybroadpeakat2=44.88°andthereflectionscorrespondingtothe(111)planeofaface-centeredcubic(fcc)phaseofnickelcouldbeobserved,whichconsistedwiththephosphoruscontents5.6wt.%ana-lyzedbyEDS.Thispatternindicatesthatthestructureoftheas-depositedNiPcoatingwasamixtureofamorphousandnano-crystallinenickel23.AlthoughthephasesinthepretreatmentlayercannotbedetectedbyXRD,thepalecoloredsurfacemayimplythepresenceofpassivefilmonthesubstance.Thesurfacemor-Fig.3.PolarizationcurvesofAZ91Dmagnesiumalloysubstrateandthesubstratewithdifferentlayersina3wt.%NaClaqueoussolution.(a)Themagnesiumalloysubstrate,(b)substratewiththeCHFP,(c)substratewiththeNiPlayerdepositedonCH+HFPlayer,(d)substratewiththeNiPlayerdepositedonCHFPlayer.phologiesoftheAZ91DmagnesiumalloysubstrateandthepretreatmentlayerwereobservedusingSEM,showninFig.2(a)and(b),respectively.Athinfilmcanbeclearlyshownonthepretreatmentsurface.Elementsurfacescreeninganalysis(omit-tedfigure)onthesetwosurfacesshowedthatthatbesidesMg,AlandZn,phosphorusandmanganeseelementsexistonthepretreatmentsurface；theirconcentrationsinthelayeranalyzedbyEDSwere0.84and0.11wt.%,respectively.Whileasforsubstrate,thecontentswere0.07and0.02wt.%,respectively,Table3CorrosionpotentialandcorrosioncurrentdensityvaluesobtainedfromtheelectrochemicalpolarizationcurvesSamplesCorrosionpotentialvs.Ag/AgCl,Ecorr/VCorrosioncurrentdensity,icorr/Acm2(a)Substrate1.502411.8(b)SubstratewiththeCHFPlayer1.44248.91(c)SubstratewiththeNiPlayeronCH+HFPlayer0.78117.79(d)SubstratewiththeNiPlayeronCHFPlayer0.59915.98Fig.4.SEMimagesoftheelectrolessNiPcoatingafter1honAZ91Dmagnesiumalloysurface(a),itscorrespondingcross-section(b)andqualitativechemicalanalyses(c),scanningfromthecoatingsurfacetothesubstratealongthelinelabeledinthefigure.