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外文翻译--镁合金化学镀镍的空隙率研究 英文版.pdf

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外文翻译--镁合金化学镀镍的空隙率研究 英文版.pdf

electrolessa,Universityform23resistanceAppliedSurfaceScience25220061.IntroductionMagnesiumisthelightestofallmetalsusedasthebaseforconstructionalalloys.Therequirementtoreducetheweightofcarcomponentshastriggeredrenewedinterestinmagnesium.Inaddition,theuseofmagnesiumalloysinotherfields,suchasaerospace,electronicandtelecommunicationcomponents,hasalsoincreasedsteadilyinrecentyears.Thegrowthrateoverthenext10yearshasbeenestimatedtobe7perannum.However,magnesiumisintrinsicallyhighlyreactiveanditsalloysusuallyhaverelativelypoorcorrosionresistance,whichisactuallyoneofthemainobstaclestotheapplicationofmagnesiumalloys1–3.Electrolessnickel–phosphoruscoatingonmagnesiumalloysisgenerallybetterthantheelectroplateddepositsbecauseoftheirenhancedcorrosionresistanceandtheiruniformityachievableoncomplexobjects.Electrolessnickel–phosphoruscoatingonmagnesiumalloysisoneofthemostappropriatemethodstofurtherenhancethecorrosionresistance.Correspondingauthor.Tel.862483687731fax862423981731.Emailaddressmengsuo66163.comJ.Li.01694332/–seefrontmatter2005ElsevierB.V.Allrightsreserved.doi10.1016/j.apsusc.2005.04.028KeywordsMagnesiumalloyElectrolessnickelplatingPorosityCorrosionAbstractInthepresentpaper,theporosityoftheplatingcoatingwasevaluatedbythecombinationofcorrodkoteandfilterpaper,theeffectsoftheplatingsolutionontheporositywereinvestigated,andthepropertiesoftheporouscoatingswerestudiedthroughscanningelectronmicroscopySEMandelectrochemicalpotentiodynamicpolarization.TheresultsshowthattheeriothromeblackTindicatorusedasanindicatorofthecoatingporosityforcoatingsonmagnesiumalloyismoreeffectivethanmagnesonindicatorandsodiumalizarinesulfonateindicator.Theporosityinelectrolessnickeldepositsonmagnesiumalloywaswellevaluatedbythecombinationofcorrodkoteandfilterpaper.Itisrevealedthattheporesexistonbothgrainsurfaceandgrainboundaries.Anaffectingtrendoftheplatingbathparametersonthecoatingporositywasobtained.2005ElsevierB.V.Allrightsreserved.StudiesoftheporosityinonmagnesiumJianzhongLia,,YanwenTianaSchoolofMaterialsandMetallurgy,NortheastbDepartmentofChemistry,SimonFraserReceived2December2004receivedinrevisedAvailableonlinenickeldepositsalloyZhenqiHuanga,XinZhangbernUniversity,Shenyang110004,China,Burnaby,BC,CanadaV5A1S623April2005accepted23April2005May2005www.elsevier.com/locate/apsusc2839–2846Eachsystemhasitsadvantagesanddisadvantages.Intheelectrolessplatingprocess,alargeamountofH2gasbubblesandimpurityparticlesareproduced,andthatmayleadtotheporeformation4–8.However,thenickelmagnesiumsystemisaclassicalexampleofcathodiccoatingonananodicsubstrate.Hence,coatingporositymightinfluencethecorrosionbehaviorandservicelifetimeoftheelectrolessnickelplatedmagnesium.Theprotectiveabilityofelectrolessnickelonmanyengineeringmaterialsislimitedbythecoatingporosity.Inaddition,thedensityandtoughnessofcoatingisintensivelyinfluencedbythecoatingporosity.ItisofactualsignificancetoinvestigatetheporosityoftheelectrolessplatingcoatingonmagnecorrosionresistanceofNi–Pcoatingbrokengradually13–15.Accordingtoacolorreactionbetweentheelementofthesubstrateandthecorrosionsolutionpassingthroughtheopeningholes,thecoatingporositywasevaluatedbythecombinationofcorrodkoteandfilterpaperinthisresearch.Theeffectoftheplatingparametersonthecoatingporositywasstudiedindetail.2.Experimental2.1.ElectrolessplatingonmagnesiumalloyThesubstratematerialusedintheresearchwasAZ91Dcastingmagnesiumalloy.ThechemicalcompositionofthealloyisgiveninTable1.Thesampleswithasizeof50mmC240mmC220mmwereusedintheexperiment.Thesubstratesweremechanicallypolishedwithemerypapersupto1000grittoensuresimilarsurfaceroughness.ThepolishedsampleswerethoroughlywashedwithJ.Lietal./AppliedSurfaceScience25220062839–28462840Distilledwaterrinsingsiumalloysindetail.Sofar,therearefewreportsonhowtoevaluatetheporosityoftheelectrolessplatingcoatingonmagnesiumalloysandwhateffectofthebathparametersonthecoatingporosity9–15.ThestructureofthecoatingporositycanbeexpressedasshowninFig.1.ThesearetwokindsofporeoneistheopeningholesD,E,theothersistheclosedoneA,B,C.Theclosedholesmostlyhaveaneffectontheeffectivethicknessandstressofthecoating,buttheopeningholewillaffectthecorrosionresistanceoftheplatingcoating.TheopeningholeDcanbecausedbythedeficiencyofthesubstrate.Thereasonisthatthedeficientspotofmagnesiumalloyseasilyreactswiththeplatingbath,producingH2gas.Thiswillleadtothediscontinuouselectrolessplatingonthedeficientspotofmagnesiumalloys.ContinuousdepositionofNi–PcoatingresultsintheoverlapoftheporesothattoformtheopeningholeE.Aprimarycellmaybeformedbetweenthecorrosionsolutionandthesubstratethroughtheopeninghole,leadingtotheFig.1.Shapestructureoftheporosityofthecoating.Picklingin125gLC01chromicacidand110mLLC01nitricacidfor45–60sDistilledwaterrinsingFluorideactivationinHF250mLLC01,70HFsolutionfor10minDistilledwaterrinsingTable1ChemicalcompositionoftheAZ91Dalloyinwt.AlMnNiCuZnCaSiKFeMg9.10.170.0010.0010.640.010.010.010.001BalanceTable2TheprecleaningprocedureUltrasonicdegreasinginacetoneImmersionin10NaOHaqueoussolutionat608Cfor5minJ.Lietal./AppliedSurfaceScience25220062839–28462841distilledwaterbeforetheprecleaningprocedureasshowninTable2.Immediatelyafterthefluorideactivationthelaststepintheprecleaningprocedure,thespecimenswerequicklytransferredtotheplatingbath1000mLinaglasscontainerplacedinawaterbathwithaconstanttemperatureof808C.Afreshbathwasusedforeachexperimenttoavoidanychangeinconcentrationofbathspecies.ThebathcompositionsandtheplatingparametersusedintheexperimentsaregiveninTable3.2.2.PorosityevaluationThecoatingporosityofthesampleplatedfor1hwasevaluatedbythecombinationofcorrodkoteandfilterpaper.Inaddition,thecorrespondingcoatingthicknessmmofthesampleplatedfor1hwascalculatedfromtheweightgain.ThecorrodkoteTable3ThebathcompositionandplatingparametersBathspeciesandparametersQuantityBasicnickelcarbonate2NiCO3C13NiOH2C14H2OgLC0111.5SodiumhypophosphitegLC0120ButanediacidgLC015AmmoniumbifluoridegLC0115HydrofluoricacidmLLC011SodiumacetategLC0120SodiumcarbonategLC01ThioureamgLC011.5AmmoniumhydroxideAdjustingpHpHvalue6.3Temperature8C80C62solutionwasmadebydissolving5mLHCland6gNaClin100mLdistilledwater.Whenthecoatedspecimenswereimmersedinthecorrodkotesolutionfor5min,thesubstratestartedtobeerodedbythecorrosionsolutionthroughtheopeningholes.Theionsofsubstrateelementwereproduced.Andthen,thespecimenwasimmersedintoanindicatorsolutionfor3min.Theindicatorsolutionmaybeoneofthreefollowingsolutionsa0.5gLC01eriothromeblackTindicatorsolutionb0.01gLC01magnesonindicatorsolutionc0.1gLC01sodiumalizarinesulfonateindicatorsolution.Acolorreactiontookplacebetweentheionsofsubstrateelementandthecorrespondingindicator.TheimmersedspecimenwasMorphologyofthehighandlowporosityofcoatingswasanalyzedbyascanningelectronmicroscope.Potentiodynamicpolarizationcurvesweremeasuredinaglasscellwiththecoatedmagnesiumalloyspecimenexposedarea1cm2astheworkingelectrode.ThecounterelectrodewasaplatinumchipandasaturatedcalomelelectrodeSCEwasusedasthereferenceelectrode.Thescanningratewas0.2mV/s.3.Resultsanddiscussion3.1.EffectofindicatorsontheporosityFig.2showsthevariationoftheporositywithdifferentindicatorsasafunctionofthemassconcentrationratioofhypophosphitetobasicnickelcarbonate.ItcanbeseenfromFig.2thattheporositiesdecreasewiththeincreaseoftheratioofhypophosphitetobasicnickelcarbonateintherangeof1.0–1.75,andthentheporositiesincreasewiththeratiointherangeof1.75–2.5.Thereasonsmaybethattheautocatalyticelectrolessnickeldepositionisinitiatedbycatalyticdehydrogenationofthereducingagentwiththereleaseofhydrideions,inwhichthenthehydrideionssupplyelectronsforthereductionofnickelion,accompaniedtheH2gasproduced.Whentheratioisintherangeof1.0–1.75,whichmeansaimmediatelydrawnontoapieceoffilterpaper.Theporositywasindicatedbythecolorpointsonthefilterpaper.Theporositywascalculatedaccordingtothefollowingequation2.18,16Porosity¼ns2.1wherenisthenumberofcolorspotssthesurfaceareaofthecoating.Inaddition,ntakescountofonespot,whenthediameterofcolorspotisbelow1mmntakescountofthreespotsasthediameterofcolorspotintherangeof1–3mmIntherangeofabove3mm,ntakescountof10spots.Triplicateexperimentswereconductedineachcase,andthefinallyevaluatedporosityofthecoatingistheaverageofthreeexperimentresultstoreduceoccasionaldataerrors.2.3.CharacterizationsoftheporouscoatingsJ.Lietal./AppliedSurfaceScience25220062839–28462842relativelylowerconcentrationofthereducingagent,thedrivingforceofthereactionisdecreased,leadingtoaslowergrowthrateoftheplatingcoating.Slowergrowthrateresultsinmoredefectsonthesubstratesurfaceduetotheaciderosionandthushighercoatingporosity.Withtheincreaseoftheratio,thegrowthrateofcoatingincreases.ThisisalsoevidencedbythecorrespondingcoatingthicknesslabeledinFig.2.TheincreaseofgrowthratehelpstopreventthesubstrateFig.2.Porositydataoftheplatingcoatingsresultedfromdifferentindicators.surfacefromacidcorrosionandthusadecreaseofcoatingporosity.Atlowerratio,thecoatingporosityismainlyresultedfromthedefectsonthesubstratesurface.Intherangeoftheratioabove1.75,muchlargeramountofH2gasisproduced,andtheplatingbathmaydecomposeorprecipitatespontaneouslyduringplating,resultinginasmallereffectiveconcentrationofthereducingagent.Thegrowthratedecreaseswiththeratio,duetothelargeamountofgasbubblesorprecipitatestrappedinthecoatings.Therefore,higherratioalsoresultsinhigherporosity7,8.Thisindicatesthatathigherratiotheimpurityparticlesandgasbubblesintheplatingbathhavearemarkableeffectonthecoatingporosity.Itshouldbealsonotedthatcoatingswithhigherporosityofferlessgrowthsitesoncoatingsurface,resultinginalowergrowthrateduringplating.ThisisevidencedbyFig.2,inwhichanincreaseofcoatingporosityisaccompaniedbyadecreaseofcoatingthicknessandviceversa.ItcanbeseenfromFig.2that,forthesamplespreparedundersameconditions,theporosityvaluesfromtheeriothromeblackTindicatorarebiggerthanthosefrommagneson,andthecorrespondingporosityvaluesfromsodiumalizarinesulfonateindicatorarethelowest.Theoretically,theporosityofthecoatingspreparedundersameconditionsshouldbethesame.Basedonobservations,thedifferenceinmeasuredvaluesofcoatingporositycanbeexplainedasthefollowing.Whenthecoatingporosityisevaluatedwiththemagnesonindicator,magnesiumionsfromthesubstratereactwiththemagnesonindicatortoformaninsolublemagnesiumcomplexleadingtothecorrespondingcolorreactionintheopeningholes.Theinsolublemagnesiumcomplexmakesithardertorevealtheholeswithsmallerdiametersonfilterpaper.Whenthecoatingporosityisevaluatedwiththesodiumalizarinesulfonateindicator,aluminumionsfromthesubstratereactwiththeindicatortoformaninsolublealuminumcomplexleadingtothecorrespondingcolorreaction.Sincethesubstrateonlycontains9.1aluminum,theconcentrationofaluminumionsismuchlessthanthatofmagnesiumioninthecolorreaction.Therefore,boththeinsolubilityandthelessavailabilityofthecoloringaluminumcomplexresultinthatonlyholeswithlargerdiametercanberevealedonfilterpaper.Incontrast,thesolublemagnesiumcomplexproducedbythecolorreactionbetweenthemagnesiumionsandtheeriothromeblackT,whicheasilypassthroughtheopeningholesandhasbetterwettabilitytofilterpaper,canrevealholeswithsmallerdiameters16.Althoughthereisthevaluedifference,theresultsfromthreeindicatorsindicatesimilartrendsincoatingporosity.Allthreeindicatorscanbeusedtoevaluatecoatingporosity.However,theeriothromeblackTwaschosenastheindicatorforotherporosityexperiments,sincethecolorpointsonfilterpaperproducedbytheeriothromeblackTtreatedcoatingsareeasiertoread.3.2.EffectofplatingparametersontheporosityFigs.3and4showeffectofthedifferentligandonporosityoftheplatingcoatingwiththeeriothromeblackTasanindicator.ThecorrespondingthicknessofthecoatingsfromplatingbathswithadditionofdifferentligandisgiveninTable4.Theconcavecurvesrepresenttheplotsofcoatingporosityagainst

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