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外文翻译--高耐腐蚀涂层的纳米镍AZ91D镁合金 英文版.pdf

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外文翻译--高耐腐蚀涂层的纳米镍AZ91D镁合金 英文版.pdf

ystallineMaterials,130025,15paper.ThesurfacemorphologiesofthecoatingswerestudiedbySEM1.Introductionresistance,solderability,electricalconductivityordecorativeappearance.Thiscanbeaccomplishedbycoatingthepartswithametalthathasthedesiredpropertiesnecessaryfortheelectrolessnickelplatingandzincimmersion2.Itcanbenotedthatinmanypreviousreportsontheelectrolessplatingonmagnesiumalloys3–6,thenickelionsweretheplatingbath.SurfaceCoatingsTechnology200Magnesiumisbecomingincreasinglysignificantasalightweightmetalstructuralmaterialwithadensityof1.74g/cm3inmanyindustriesaircraftconstruction,spacetechnology,optics,andautomobilemanufacturing,forexample.However,magnesiumisintrinsicallyhighlyreactiveanditsalloysusuallyhaverelativelypoorcorrosionresistance,whichrestrictstheapplicationofmagnesiumalloysinpracticalenvironments.So,itisoftendesirabletoalterthesurfacepropertiesofamagnesiumormagnesiumalloyworkpieceinordertoimproveitscorrosionandwearspecificapplication1.Sincemagnesiumisoneofthemostelectrochemicallyactivemetals,anycoatingsonmagnesiumalloysshouldbeasuniform,adheredandporefreeaspossible.Oneofthemostcosteffectiveandsimpletechniquesforintroducingametalliccoatingtoasubstrateistheplatingtechniques,includingelectrolessplatingandelectroplating.Furthermore,magnesiumisclassifiedasadifficultsubstratetoplatemetalduetoitshighreactivity.Asforelectroplatingonthemagnesiumalloy,therearecurrentlytwoprocessesusedforplatingonmagnesiumandmagnesiumalloysdirectandFESEM.ThencNicoatinghadanaveragegrainsizeofabout40nmandanevident{200}preferredtexturerevealedbyXRD.ThehardnessofthencNicoatingwasabout580VHN,whichwasfarhigherthanthatabout100VHNoftheAZ91Dmagnesiumalloysubstrate.TheelectrochemicalmeasurementsshowedthatthencNicoatingonthemagnesiumalloyhadthelowestcorrosioncurrentdensityandmostpositivecorrosionpotentialamongthestudiedcoatingsonthemagnesiumalloy.Furthermore,thencNicoatingontheAZ91Dmagnesiumalloyexhibitedveryhighcorrosionresistanceintherapidcorrosiontestillustratedinthepaper.ThereasonsforanincreaseinthecorrosionresistanceofthencNicoatingonthemagnesiumalloyshouldbeattributabletoitsfinegrainstructureandthelowporosityinthecoating.D2005ElsevierB.V.Allrightsreserved.KeywordsNanocrystallinenickelMagnesiumalloyElectroplatingElectrolessnickelCorrosionmagnesiumalloywithdifferentthicknesswerealsopresentedintheAbstractNanocrystallinencNicoatingwasdirectcurrentelectrodepositedontheAZ91Dmagnesiumalloysubstrateaimedtoimproveitscorrosionresistanceusingadirectelectrolessplatingofnickelastheprotectivelayer.Ascomparison,twoelectrolessNicoatingsontheHighcorrosionresistancenanocrmagnesiumChangdongGu,JiansheLian,JinguoKeyLabofAutomobileMaterials,MinistryofEducation,CollegeofChangchunReceived22March2005acceptedAvailableonline02578972/seefrontmatterD2005ElsevierB.V.Allrightsreserved.doi10.1016/j.surfcoat.2005.07.001Correspondingauthor.Fax864315095876.Emailaddresslianjsjlu.edu.cnJ.Lian.NicoatingonAZ91DalloyHe,ZhonghaoJiang,QingJiangScienceandEngineering,JilinUniversity,NanlingCampus,Chinainrevisedform4July2005August200520065413–5418www.elsevier.com/locate/surfcoatprovidedbybasicnickelcarbonateinDifferentfromthemethodsmentionedabove,directelectrolessnickelplatingontheAZ91Dmagnesiumalloywasquicklyaspossiblebetweenanytwostepsofthetreatments.ThedirectelectrolessnickelplatingwiththehardnesstesterwithVickersindenter,ataloadof100ganddurationof15s.ElectrochemicalmeasurementswereperformedonanElectrochemicalAnalyzerCHI800,Shanghai,China,whichwascontrolledbyacomputerandsupportedbysoftware.LinearSweepVoltammetryexperimentswerecarriedoutina3wt.NaClaqueoussolutionusingaclassicthreeelectrodecellwithaplatinumplatePtascounterelectrodeandanAg/AgClelectrode207mVvs.SHEasreferenceelectrode.Beforetesting,theworkingelectrodewascleanedinacetoneagitatedultrasonicallyfor10min.TheexposedareafortestingwasobtainedbydoublycoatingwithepoxyresinEP651leavinganuncoveredareaofapproximately1cm2.Thereferenceandplatinumelectrodeswerefixedneartotheworkingelectrodeabout0.5mm,whichcouldminimizetheerrorsduetoIRdropintheelectrolytes.Duringthepotentiodynamicsweepexperiments,thesampleswerefirstimmersedinto3wt.NaClsolutionforabout20mintostabilizetheopencircuitpotential.Potentiodynamiccurveswererecordedbysweepingtheelectrodepotentialfromavalueofabout300–400mVlowertoavalueof500–600mVupperthanthecorrosionpotential,respectively,atasweepingrateof5mV/s.Thelogi–EcurveswereTime30minabout15µmFig.1.ThetechnicalflowchartoftheelectroplatingncNiontheAZ91Dmagnesiumalloy.Technologythicknessofabout10AmonAZ91Dmagnesiumalloy7wasusedastheprotectivelayerforfurtherplatingonthemagnesiumalloy.TheelectroplatingncNicoatingonthemagnesiumalloywasdirectcurrentelectroplatedfromabathcontainingnickelsulfate,nickelchloride,boricacidandsaccharinatapHof5.0andatemperatureof50C.Duringtheelectrodepositionprocess,theanodewasusedanelectrolyticnickelplate.TheoperationofelectroplatingncNicoatingwasundertakenforabout30minwhichwouldgivethecoatingwiththethicknessofabout15Am.AscanningelectronmicroscopeSEM,JEOLJSM5310,JapanandafieldemissionscanningelectronmicroscopeFESEM,JEOLJSM6700F,JapanwereemployedfortheobservationsofthesurfaceofthecoatingsandthecrosssectionmorphologyandanEDXattachmentwasusedforqualitativeelementalchemicalanalysis.CrystallinestructureofthesamplewasstudiedbytheXraydiffractometerXRD,RigakuD/max,JapanwithaCutargetandamonochronmatorat50kVand300mAwiththescanningrateandstepbeing4/minand0.02,recentlyundertakenbyusingaplatingbathcontainingsulfatenickel7.Intherecentyears,therehavebeenconsiderableinterestsinunderstandingthemechanicalproperties,thecorrosionresistanceandthewearresistanceofncmetalsproducedbyelectrodeposition,forexample8–14.Accordingtothem,ncmaterialsexhibitedmanyunusualmechanicalandelectrochemicalpropertiescomparedwithconventionalpolycrystallineoramorphousmaterials.Sointroducinganccoatingcombinedthehighcorrosionresistancewithgoodwearresistanceonmagnesiumalloysubstratewouldbeverypromising.Inthepresentpaper,theelectrolessNiplatingfromanacidicbath7wasfirstdepositedonAZ91Dmagnesiumalloyastheprotectivelayerforthefurtherelectroplatingoperation,andthenancnickelcoatingwasdirectcurrentelectroplatedontheprotectivelayer.ThemicrostructuresandtheelectrochemicalpropertiesofthecoatingsontheAZ91DmagnesiumalloysubstratewerestudiedbySEM,FESEM,XRDandelectrochemicalmeasurement.2.ExperimentalThesubstratematerialusedwasAZ91Ddiecastmagnesiumalloywithasizeof30C240C25mm.Thealloywasmainlycontainedabout9.1Al,0.64Zn,0.17Mn,0.001FeandMgbalance.Thesampleswereabradedwithno.1500SiCpaperbeforethepretreatmentprocesses.ThetechnicalflowchartoftheelectroplatingontheAZ91DmagnesiumalloyisshowninFig.1.ThesampleswerecleanedthoroughlywithdeionizedwaterasC.Guetal./SurfaceCoatings5414respectively.ThehardnessofthemagnesiumalloyandthecoatingswereevaluatedusingaHXD1000microAlkalinecleaningNaOH45g/lNa3PO412H2O10g/lTemperature65°CAcidpickleCrO3125g/lHNO370V/V100ml/lTime40sRoomtemperatureFluorideactivationHF40V/V350ml/lTime10sRoomtemperatureElectrolessplatingprotectivelayerref.7Time15minabout10µmElectroplatingnanocrystallineNiNiSO46H2O250300g/lNiCl26H2O3040g/lH3BO33045g/lC7H5NO3S0.10.2g/lCurrentdensity3A/dm220020065413–5418measuredandplottedaftertheaboveelectrochemicalmeasurements.ThecorrosionpotentialEcorrandcorrosioncurrentdensityicorrweredetermineddirectlyfromtheselogi–EcurvesbyTafelregionextrapolation.Acidimmersiontestin10HClsolutionatroomtemperaturewasundertakentotestthecorrosionresistanceofthencNicoatingonthemagnesiumalloy.Ifthereweremicroporesinthecoatings,thecorrosionsolutionwoulderodethemagnesiumsubstratethroughthepores.Duetothehighchemicalactivityofthemagnesium,theHinthecorrosionsolutionwouldbereducedbythemagnesiumandturnedintothehydrogengasbubbles.Sothetimeintervalbetweenthestartofthetestandthefirsthydrogengasbubblearisingfromthecoatingsurfacecouldbeusedtodonatethecorrosionresistanceofthecoatingsonthemagnesiumalloysubstrate.Forcomparison,theelectrolessplatingnickelcoatingswithdifferentthickness10and25Amwerealsotestedinthepaper.3.Resultsanddiscussions200peakviatheScherrerequation16dXRD¼kkbhðÞcoshð1ÞWherekistheXraywavelength,btheFWHMfullwidthofhalfmaximumofthe200diffractionpeak,hthediffractionangleandtheconstantkC2291.FromEq.1theaveragegrainsizeofthisncNiwasabout40nm.Inaddition,theXRDresultsalsoshowedthatthencNicoatinghadanevident{200}preferredtexture.Infact,Nielectrodepositsareknownforgivingnumerous,welldefinedpreferredorientationsdependingonelectrodepositionconditions,i.e.electrolytecomposition,temperature,pH,currentdensity,stirringandorganicadditions17,18.The{200}preferredtextureofthencNiinthisstudymaybeattributabletothegivenelectrodepositionconditionswhichmayleadtohigherelectrodeoverpotentialandreducedconcentrationofNi2attheelectrodesurface18.Fig.3ashowedthetypicalsurfacemorphologyoftheasdepositedncNicoating.ItcanbeseenthattheasdepositedsurfaceofthencNicoatingwasverycompactandnocolonystructures,whichwastotallydifferentfromthecauliflowerlikeinmicrometersizesurfacemorphologyoftheelectrolessnickeldepositionseeFig.3b.Moreover,theasdepositedsurfaceofthencNicoatingexhibitedaflatandmirrorlikeappearanceandthe25000NiC.Guetal./SurfaceCoatingsTechnology20304050607080050001000015000200002030405060708005001000150020002500a2θ/deg.20304050607080050010001500bIntensity/CPSMg17Al12MgcFig.2.TheXRDpatternsoftheelectroplatingNiontheAZ91Dmagnesiumalloyatdifferentintervals,aAZ91Dmagnesiumalloy3.1.MicrostructuresandhardnessofthecoatingsFig.2ashowedthepatternofXRDoftheAZ91Dmagnesiumalloy,whichindicatedthatthesubstratealloyconsistedofprimaryaMggrainssurroundedbyaneutecticmixtureofaandbMg17Al1215.ItalsocanbeseenfromtheXRDpatternofFig.2bandthemorphologyofFig.3thatafterelectrolessNiplatingforabout15min,theAZ91Dmagnesiumalloywasfullycoveredbytheelectrolessnickeldeposition.Thephosphoruscontentintheelectrolessdepositionwasverylow,becauseNiwasfirstdepositedonthesurfaceofmagnesiumalloyaccordingtothedepositionmechanismofelectrolessplatingonthemagnesiumalloy7.TheXRDanalysisresultsoftheasdepositedelectroplatingncNicoatingwasshowninFig.2substrate,belectrolessplatingonthesubstratefor10min,ctheelectroplatingncNicoating.c.ThegrainsizedofncNicanbedeterminedfromtheFig.3.ThesurfacemorphologyofathencNicoatingandbtheelectrolessnickelplatingontheAZ91Dmagnesiumalloyforabout10min.20020065413–54185415grainsizeofthedepositscouldnotberesolvedbyconventionalSEMobservations.Inordertomakeaclearobservationofthefinegrainstructure,specimenofthisncNiwaspolishedandcorrodedbydilutenitrate/ethanolsolutionbeforetheSEMobservation.ThesurfacemorphologyofthencNiafterabovepretreatmentswasshowninFig.4.TheveryuniformncgrainstructurescanbeseenonthesurfaceofncNiafterslightlycorroded.Fig.5ashowedthecrosssectionmorphologyofthencNicoatingontheAZ91Dmagnesiumalloy.ToindicatethesubstrateandtwotypesoftheNilayersonthecrosssectionofthecoating,thesubstrate,theprotectivelayerandthencNilayerweremarkedbythelinewithtwoarrows,respectively,intheFig.5a.Fromthisfigure,itcanbeseenthattheacidpicklepretreatmentpriortoelectrolessplatingprotectivelayerforthemagnesiumalloyprovidessurfacepitstoactassitesformechanicalinterlockingtoimproveadhesion7.Moreover,therewerenoobviousboundariesbetweentheprotectivelayerandthencNilayer,whichindicatedthatthencNilayerwastightlyattachedtotheprotectivelayer.Inaddition,thencNilayershowedverycompactandnoporesfromitscrosssectionobservation.Fig.5bgavethequalitativeelementanalysisofthencNicoatingontheAZ91DmagnesiumalloybyEDXanalysis.ForthelowerphosphorouscontentintheprotectivelayerpreviousdepositedontheAZ91Dmagnesiumalloysubstrate,thedistributionofelementofphosphorouswasnotdetectedbyEDX.FromtheelementsdistributingfromthesubstratetothecoatingsurfacealongthelinelabeledinFig.5a,itcanbeseenthatthecoatingwasconnectedcloselytothemagnesiumalloysubstrate.Fig.4.ThesurfacemorphologyoftheelectroplatedncNicoatingafterpolishingandcorrodedbydilutenitrate/ethanolsolution.C.Guetal./SurfaceCoatingsTechnology20020065413–54185416Fig.5.aThecrosssectionmorphologyoftheNicoatingontheAZ91DmagnesiummagnesiumalloybyEDXanalysis,scanningfromthesubstratetothecoatingsurfacealloy,bthequalitativeelementanalysisofcoatingontheAZ91Dalongthelinelabeledinthefigure.

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