外文翻译--以硫酸镍为主盐的镁合金化学镀镍 英文版.pdf

mainbinrevised2613.electrolessplatingsolutionsandlittleapplications.Inaddition,thebasicnickelcarbonateornickelacetateofareharmfultotheSurface&CoatingsTechnology2001.IntroductionTheuseofmagnesiumalloysinavarietyofapplications,particularlyinaerospace,automobiles,andmechanicalandelectroniccomponents,hasincreasedsteadilyinrecentyearsasmagnesiumalloysexhibitanattractivecombinationoflowdensity,highstrength-to-weightratio,excellentcast-ability,andgoodmechanicalanddampingcharacteristics.However,magnesiumisintrinsicallyhighlyreactiveanditsalloysusuallyhaverelativelypoorcorrosionresistance,whichisactuallyoneofthemainobstaclestotheapplicationofmagnesiumalloysinpracticalenvironmentsHence,theapplicationofasurfaceengineeringtechniqueisthemostappropriatemethodtofurtherenhancethecorrosionresistance.Amongthevarioussurfaceengineeringtechniquesthatareavailableforthispurpose,coatingbyelectrolessnickelisofspecialinterestespeciallyintheelectronicindustry,duetothepossessionofacombinationofproperties,suchasgoodcorrosionandwearresistance,deposituniformity,electricalandthermalconductivity,andsolderabilityetc.Asfarasmagnesiumalloysareconcerned,themainsaltsofelectrolessplatingsolutionsmostlyfocusattentionsonbasicnickelcarbonateornickelacetate49,whichresultinhigh-cost,low-efficiency,instabilityofAbstractInthispaper,theelectrolessnickel-platingonmagnesiumalloywasstudied,usingNiSO4d6H2Oasthemainsaltintheelectrolessplatingalkalinesolutions.Theeffectsofthebufferagentandplatingparametersonthepropertiesandstructuresoftheplatingcoatingsonmagnesiumalloywereinvestigatedbymeansofscanningelectronmicroscopy(SEM),energydispersiveX-rayspectroscopy(EDS)andX-raydiffraction(XRD).Inaddition,theweightloss/gainofthespecimensimmersedinthetestsolutionandplatingbathwasmeasuredbyusingtheelectro-balance,toevaluatetheerosionofthealloyintheplatingsolutions.Theadhesionbetweentheelectrolessplatingcoatingsandthesubstrateswasalsoevaluated.Thecompositionsofthenon-fluorideandenvironmentallyfriendlyplatingbathwereoptimizedthroughLatinorthogonalexperiment.Thebufferagent(Na2CO3)addedtotheplatingbathwasfoundtobeusefulinincreasingthegrowthrateoftheplatingcoating,adjustingtheadhesionbetweentheelectrolessplatingcoatingsandthesubstrates,andmaintainingthepHvaluewithintherangeof8.511.5,whichisrequiredforthesuccessfulelectrolessnickel-platingonmagnesiumalloywithNiSO4d6H2Oasthemainsalt.Trisodiumcitratedihydratewasfoundtobeanessentialcomponentoftheplatingbathtoplatemagnesiumalloy,withanoptimumconcentrationof30gLC01.Theobtainedplatingcoatingsarecrystallinewithpreferentialorientationof(111),havingadvantagessuchaslow-phosphoruscontent,highdensity,low-porosity,goodcorrosionresistanceandstrengthenedadhesion.D2004ElsevierB.V.Allrightsreserved.Keywords:Magnesiumalloy；Electrolessplating；Buffer；Corrosionresistance；AdhesionTheelectrolessnickel-platingonmagnesiumastheJianzhongLia,*,ZhongcaiShaoaSchoolofmaterialsandmetallurgy,NortheastebFacultyofEnvironmentandChemicalEngineering,ShenyangReceived23July2004；acceptedAvailableonline0257-8972/$-seefrontmatterD2004ElsevierB.V.Allrightsreserved.doi:10.1016/j.surfcoat.2004.12.009*Correspondingauthor.Tel.:+862483687731；fax:+862423981731.E-mailaddress:mengsuo66163.com(J.Li).alloyusingNiSO4d6H2Osalt,XinZhanga,YanwenTianarnUniversity,Shenyang110004,ChinaInstituteofTechnology,Shenyang110168,Chinaform19December2004January2005(2006)30103015www.elsevier.com/locate/surfcoattodevelopnewplatingsolutionsyetincludingfluoride,environment,therefore,itisurgentlyneededenvironmentallyfriendlyplatingbath.Itisdifficulttocarryoutelectrolessplatingonmagnesiumalloysduetothehigh-corrosionrateofmagnesiumalloysintheplatingbathwithNiSO4d6H2OorNiCl2d6H2Oasthemainsalt.Itisreported10thatthecorrosionrateofmagnesiumanditsalloysinNaClsolutionssolelydependsonthepHofthebufferedchloridesolutions.TheobjectiveofthisstudywastofindabufferagentanddeterminehowthebufferagentaffectsthedissolutionofmagnesiumalloyinNiSO4d6H2Oalkalinesolutions,andthenon-fluorideplatingsolutionsformagne-siumalloywithNiSO4d6H2Oasthemainsalt.Themicrostructure,compositionsandcorrosionbehaviorofthecoatingswereinvestigatedindetail.constanttemperatureof808C.Afreshbathwasusedforeachexperimenttoavoidanychangeinconcentrationofbathspecies.ThebathcompositionsandotherparametersusedintheseexperimentsaregiventhroughLatinorthogonalexperimentinTable3.Table1ChemicalcompositionoftheAZ91Dalloy(inwt.%)AlMnNiCuZnCaSiKFeMg9.10.170.0010.0010.64b0.01b0.01b0.01b0.001BalJ.Lietal./Surface&CoatingsTechnology200(2006)301030153011Table2Optimizedpre-cleaningprocedure2.ExperimentalThesubstratematerialusedintheresearchwasAZ91Dingot-castalloy.ThechemicalcompositionofthealloyisgiveninTable1.Substrateswithasizeof50mmC240mmC220mmwereusedintheresearch.Thesubstratesweremechanicallypolishedwithemerypapersupto1000grittoensuresimilarsurfaceroughness.Thepolishedsubstrateswerethoroughlywashedwithdistilledwaterbeforepassingthroughthepre-cleaningprocedureasshowninTable2.Thesubstrateswereair-driedafterthefluorideactivation(thelaststepinthepre-cleaningprocedure).Inatypicalexperiment,theinitialweightofaair-driedsubstratewasmeasuredandthenquicklytransferredtotheplatingbath(1000mL)inaglasscontainerplacedinawaterbathwithaFinalweightsofthespecimensweredeterminedandthecoatingratesinmicrometerperhourwerecalculatedfromtheweightgain.Atthesametime,inordertostudytheeachbuffersinfluenceonthesubstratesandfindabufferappropriatefortheelectrolessplatingonmagnesiumalloy,testsolutionswithcompositionssimilartothoseoftheplatingbathexceptthatsodiumhypophosphitewasnotadded,werepreparedtosimulatethecorrosionratesofmagnesiumalloyinplatingbathandthebehaviorsofthebuffers.Duplicateexperimentswereconductedineachcase,andthecoatingratereportedistheaverageoftwoexperiments.Thegrowthratesoftheplatingcoatingweremeasuredusingtheelectro-balancemadeinAmerica,whichisthe0.1mgprecision.Intheresearch,thepHvalueofplatingbathwasmonitoredbyapHS-25CmodelofprecisionpH/mVmeter.Morphologyofthecoatingswasanalyzedusingascanningelectronmicroscope.TheenergydispersiveX-rayspectroscopyanalysiswasusedfordeterminingthecontentofphosphorusinthecoatings.CrystallinityofthecoatingswasinvestigatedbyRigakuD/max-rAX-raydiffractometerwithCuK-alpharadiation.Theadhesionstrengthoftheelectrolesslydepositednickelcoatingstothemagnesiumalloysubstrateswasdeterminedbyscratchtest.Duringthescratchtest,thespecimenwasmovedataconstantspeedofapproximately11.4mm/min.Scratchesweregeneratedonthespecimenusingadiamondindenterwithasphericaltipof300Amindiameter.Corrosionpotentialmeasurementin3.5wt.%NaClsolutionwascarriedouttocomparativelyinvestigatethecorrosionbehaviorsofthebaresubstrateandthenickel-platedsubstrates.Theelectrochemicalcellusedforcorrosionpotentialmeasurementconsistedofabaresubstrateoranickel-platedsubstrateastheworkingelectrode(exposedarea:1cm2),asaturatedcalomelelectrode(SCE),andaplatinum-foilcounterelectrode.Table3OptimizedbathcompositionandparametersBathspeciesandparametersQuantityNiSO4d6H2O25g/LNaH2PO2dH2O30g/LC6H5Na3O7d2H2O30g/LNa2CO330g/LNH3dH2OAdjustingpHpHvalue11Temperature80F28C3.Resultsanddiscussion3.1.ThebuffersbehaviorsinthetestNiSO4solutionsandthechoiceofanappropriatebufferFig.1showsthevariationofweightlossofmagnesiumalloyasafunctionoftheimmersiontimewithdifferentbuffersinthetestsolutions.Thecompositionsandthecontrolledtemperatureofthetestsolutionsweresimilartothoseoftheplatingbathexceptthatsodiumhypophosphitewasnotincluded.ThepHvaluesofthetestsolutionswereadjustedbyNH3dH2Otofixat11.TheweightlossincreaseslinearlywiththeimmersiontimeincreasingofmagnesiumalloysintheNa2CO3,Na2B4O7,andCH3COONatestsolutions.ItisrevealedinFig.1thatthecorrosionrateswereconstantthroughouttheexaminedimmersiontime.AsrecognizedfromtheslopeofeachsolidlineinFig.1,corrosionrateinthetestsolutioncontainingNa2CO3bufferisthelowestamongthethreetestedbuffers.Theindicatestheweight-lossofthesubstratesisrelatedtothereactionbetweenthesubstratemetalandthehydrogenions.Butthecorrosionreactionbetweenthesubstratemetalandthehydrogenionsgoesgraduallyon,becausethelowconcentrationofhydrogenionsispresentedintheplatingalkalinesolutions.Andthen,theconcentrationofhydrogenionsisweaklydecreasedduringthetestprogress.Thisleadstotheconstantcorrosionratesintheshorttesttime,whichisshowninFigs.1and2.Atthesametime,knowingthatforMg(OH)2Kspat258C=8.9C210C012atpH9,OHC0=10C05M,mostMg2+diffusedintoplatingsolutiontoformupto10C02M.AtpH11,OHC0=10C03M,theMg2+couldntexceed10C06M,thusmostMg2+formedMg(OH)2andstayednearthesubstrate.Mg(OH)2couldincreasetheadsorptionenergybarrierandreducethecorrosionrate.Therefore,higherpHresultedinlowercorrosionrate.AstotheNa2CO3bufferedsolutions,forMgCO3Kspat258C=10C015,intestsolutions,Na2CO3N0.1M,thusthepossibleMg2+b10C014M.ThismeansthatthedrivingforceforMgtoformMg2+wasverylow.InsteadofdissolvingMg,theCO32C0ionwouldbondorbeadsorbedtothesubstrate2C0J.Lietal./Surface&CoatingsTechnology3012obtainedslopesare0.015,0.022and0.056mgcmC02minC01forNa2CO3,Na2B4O7andCH3COONabuffers,respectively.Theseresultscanbeexplainedintermsofdissociationconstantsofthecorrespondingacids,whicharek2=4.7C210C011(k1=4.4C210C07),k2=1C210C09(k1=1C210C04),andk=1.75C210C05forH2CO3,H2B4O7andCH3COOH,respectively.Theseconddissociationconstantofabinaryaciddecidesthebuffercapabilityofthebuffer.Obviously,theNa2CO3bufferhasthelowestcostandbestbuffercapabilityamongthetestedbuffers.Fig.2showstheweightlossofthesubstratesversusimmersiontimeinthetestsolutionswithpHvaluesat9,10and11,usingNa2CO3asthebuffer.Corrosionofthespecimensinnon-bufferedtestsolutionswithpHvaluesat9,10and11wasalsoinvestigated.ThecorrespondingweightlosscurvesareshowninFig.2.Alltestsolutions05101520253035-0.20.00.20.40.60.81.01.21.41.61.8Na(CH3COO)Na2B4O7Na2CO3Weightloss/mg.cm-2Time/minFig.1.Thevariationofweightlossofmagnesiumalloyintestsolutionswithdifferentbuffers.usedfortheseexperimentshadcompositionssimilartothoseintheplatingbathexceptthatsodiumhypophosphitewasnotincluded.TheweightlosslinearlychangeswiththeincreaseoftheimmersiontimeinallcasesshowninFig.2.UnderthesamepHvalue,thecorrosionrateofthesubstratesinthebuffersolutionisobviouslylowerthanthatofthesubstratesinthenon-bufferedsolution,asshownbytheslopesofthecurvesinFig.2.Thissuggeststhatthebuffersolutionhasaconsiderableeffectonthecorrosionrateofmagnesiumalloy.InboththeNa2CO3bufferedandnon-bufferedtestsolutions,thecorrosionratesofmagne-siumalloydecreasewiththeincreaseofthepHvalue.This05101520253035012345solutionpH=9pH=10pH=11pH=9pH=10pH=11Weightloss/mg.cm-2Time/mininnon-bufferedsolutioninNa2CO3bufferedFig.2.ThevariationofweightlossofmagnesiumalloyintestsolutionswithdifferentpHvalues.200(2006)30103015surfacetoformlocalMgCO3.Inthiscase,thesubstratesurfaceareaexposedtoH2OorH+wasreducedalot,leadingtolowercorrosionrates.ThepKa2forNa2CO3is10.33,atpHlowerthan10.33someCO32C0ionsformedHCO3C0.ReactionMg+2HCO3C0=MgCO3+H2potentiallyexisted.AtpHhigherthan10.33,HCO3C0isnegligible.ThereforeinFig.2,wecanseethatthecorrosionrateatpH11wasnotreducedasmuch,comparedtherateat10.H2B4O7andCH3COOHdonthavesuchadvantages.wasmonitoredwithapHS-25CmodelofprecisionpH/mVmeter.Inthisresearch,thepreferredpHrangeoftheplatingbathforelectrolessplatingonmagnesiumalloyis8.511.5.Table4Coatingrate,surfaceappearanceandadhesionofthecoatingsobtainedfromtheplatingbathwithdifferentamountsofNa2CO3ConcentrationofNa2CO3(gLC01)Coatingrate(Am/h)SurfaceappearanceLC(N)0Gravecorrosion1012.32Pointcorrosion812016.41Darkgray763018.32Shining734018.91Shining615019.26Shining513040506010002000300040005000600070008000IntensityJ.Lietal./Surface&CoatingsTechnology200(2006)3010301530133.2.TheeffectsofplatingparametersoncoatingsThecoatingrate,surfaceappearance,andadhesionofthecoatingsatdifferentconcentrationsofNa2CO3bufferarelistedinTable4.Thecriticalload(LC)wasmeasuredunderprogressiveloadingconditions,whichcanbeusedtoaccuratelycharacterizetheadhesionstrengthofthedeposit/substratesystem13.TheadhesionbetweenthecoatingsandsubstratesdecreasesobviouslywiththeincreaseoftheconcentrationofNa2CO3.SurfaceappearanceoftheplatingcoatingsbecomesgraduallyshiningwiththeincreaseoftheNa2CO3concentration.Gravecorrosionofthesubstrateswasfoundinthenon-bufferedplatingbath.ThegrowthrateofthecoatingsnoticeablyincreaseswiththeincreaseoftheNa2CO3concentration.Consideringthecombinationofgrowthrate,surfaceappearance,andadhesionofthecoatings,the17181920µm20304050607013141516Thecoatingthickness/Thetrisodiumcitratedihydratecontent/g.L-1Fig.3.Relationshipbetweenthecoatingthicknessandthetrisodiumcitratedihydrateconcentration.optimumconcentrationoftheNa2CO3bufferwasdeterminedtobe30gLC01.Withthisconcentration,thepurposeofaddingNa2CO3inplatingbathiscommendablyachieved.Intheresearch,itwasfoundthatthepHvalueofplatingbathhadaconsiderableeffectonthegrowthrateandthesurfaceappearanceofthecoatings.ThehydrogenionsinplatingbathwerenotonlyastrictedbytheCO32C0ionsdissociatedfromthebufferNa2CO3,butlinkedwiththeOHC0ions.WhenthepHvalueoftheplatingbathwasbelow8.5,pointcorrosionordarkgraycoatingswereobtainedandthecoatinggrowthratewaslow.WhenthepHvalueoftheplatingbathwasabove11.5,theadhesionbetweencoatingsandsubstratesweredeteriorated,althoughthegrowthrateandthesurfaceappearanceofthecoatingsweresatisfying.Duringtheelectrolessplating,thepHvalueoftheplatingbath2/(º)Fig.4.XRDpatternsoftheelectrolessplatingcoating.Fig.5.Surfacemorphologyofaplatingcoating.