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中英文翻译-铅元素对AZ91镁合金形成过程的影响.doc

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中英文翻译-铅元素对AZ91镁合金形成过程的影响.doc

EffectofPbadditiononageingbehaviorofAZ91magnesiumalloyAbstractTheageingbehaviorofAZ91alloycontaining2wt.leadisinvestigated.TheresultsshowthatadditionofPbsuppressesthediscontinuousprecipitationandtherebyslowsdowntheageingkinetics.Eventhoughthepeakhardnessobtainedforbothalloysisalmostsame,thepeakhardnessreachesafter2400minforPbaddedalloyagainst900minforthebasealloy.ThepresenceofPbinsolidsolutionmighthaveinhibitedthediffusionofAlandMgatoms,whichisessentialfortheformation,andgrowthofdiscontinuousprecipitationinthisalloy.KeywordsAZ91magnesiumalloy,Pbaddition,Ageingbehavior,Microstructure,DTA1.IntroductionMagnesiumbasedalloysareincreasinglyusedintheautomobileindustries.Thereasonsforthislieprincipallyintheirimprovedspecificpropertiescomparedwithaluminumalloysorsteelsandlightweight30lessthanAl,and75lessthansteels1.Amongthemostcommoncommercialmagnesiumalloys,AZ91isendowedwithoneofthebestcombinationsofcastability,mechanicalstrengthandductility2.Presenceofaluminumprovidesmechanicalandcastingpropertiesaswellascorrosionresistance,whereaszinccontributestosolidsolutionstrengthening.ThemaximumsolidsolubilityofaluminuminMgis12.7wt.at437◦Canddecreasingtoabout2wt.atroomtemperature.Hencecastingssandandpermanentmouldcastingsofthisalloyareheattreatedtoobtainbettermechanicalpropertiesandstudiesareavailableintheliteraturetounderstandtheageingbehaviorofthisalloy3–6.Duringsolutiontreatmentat410℃,theMg17Al12βphaseredissolvesintotheMgmatrixandformsahomogenizedsolidsolution.Onsubsequentageingatlowertemperature,aluminumprecipitatesoutintwoformsi.e.discontinuousandcontinuousprecipitates.DiscontinuousprecipitationisthecellulargrowthofalternatinglayersofphaseMg17Al12andnearequilibriummagnesiummatrixathighanglegrainboundary2,7,8.Growthofthediscontinuousprecipitationregionsceasesrelativelyearlyintheprecipitationprocess.Continuousprecipitationformsintheremainingregionsofthematrixthatarenotalreadyoccupiedbydiscontinuousprecipitates7.Itisdemonstratedthatthecontinuousprecipitatesareresponsibleforagehardening,whereasthediscontinuousprecipitatesaredetrimentaltoagehardening6.Moreover,thediscontinuousprecipitatesformedduringhightemperatureexposurecreepreducethecreeppropertiesconsiderably9.Dynamicdiscontinuousprecipitatesoccuratthegrainboundariesfromthesupersaturatedeutecticsolidsolutionleadtotheslidingofgrainboundariesandweakenthematerial9.Hencesuppressingthisdynamicdiscontinuousprecipitationduringhightemperatureexposureisinevitabletoimproveitshightemperatureproperties.Itisalsoreportedthatadditionofsomeofthetraceelementslikegoldandrareearthsuppressesthediscontinuousprecipitationduringageing10,11.Buttheseelementsarecostlier.ThepreliminarystudyonthePbadditiontoMg–7AlhasreportedthatadditionofPbhasthetendencytosuppressthediscontinuousprecipitation12.Besides,Pbischeapermaterialcomparedtogoldandrareearth.So,inthisstudyadetailedinvestigationontheeffectofPbadditionontheageingbehaviorofgravity。PermanentmoldcastAZ91alloyhasbeencarriedout.,Eventhough,thePbvaporishazardoustohealthadditionofsmallamountwithpropercarewillnotbeseriousone.TheagingbehaviorhasbeenexaminedusingBruneihardnessanddifferentialthermalanalysis,combinedwithmicrostructureobservationdevelopedduringheattreatmentbyopticalmicroscopyandscanningelectronmicroscopy.2.Experimental2.1.CastingTheAZ91magnesiumalloyusedforthisexperimentwaspreparedbymeltingtogethertherequiredquantitiesofcommerciallyavailablepureMg,pureAl,pureZnandAl–10Mnmasteralloy.Meltingwascarriedoutinasteelcrucibleintheresistancefurnaceunderproperfluxcover.Whenthemelttemperaturewas700◦C,2wt.purePbwasaddedintothemelt.Themeltwasthenrefinedat720◦Candheldfor20minfortheoxideparticlestosettle.Therefiningofthemeltwascarriedoutbystirringthemoltenmeltafteraddingtherefiningfluxintothemelt.Themeltwaspouredintoapreheated250℃diecoatedrectangularmetallicmoldhavingdimensions240mm210mm40mm.Sulphurdustingwasdoneduringpouringtoavoidburning.2.2.HeattreatmentCylindricalsamplesofsize15mmdiameterand15mmheightmachinedformthecastingsofthebaseAZ91alloyandPbaddedAZ91alloyweresolutiontreatedat410℃for48hinamuffledfurnace.ToavoidoxidationofMgalloysamplesduringsolutiontreatment,amixtureof20cokemixedwith80foundrysandbedwaskeptinsidetheovenseparatelytoabsolvetheoxygen.Theexperimentalresultsshowedthatthissimplemethodeffectivelyreducedtheoxidationofthespecmiens.Thesesampleswerethenquenchedincoldwaterandsubsequentlyagedat200℃upto50hforfurtherinvestigationsontheageingkinetics.2.3.DifferentialthermalanalysisDTAPiecesweighing20mgwerecutfromtheascastandsolutionthediscontinuousprecipitatesatgrainboundaries.ThesuppertreatedsamplesandDTAmeasurementswereperformedusingsignofMg17Al12formationiseasilyunderstandablewithXRDSETSYS16/18,SETARAMmachine.PureMgpiecewasusedanalysisperformedonthesamples.Table1givestherelativeasareference.TheDTAexperimentwascarriedoutunderargonintensityvaluesofmajorrepresentativeBraggreflectionoftheatmospherewithaheatingrateof10C/min.Temperatureversusheatflowcurvewasobtainedtounderstandtheageingbehaviorofthesealloys.2.4.MicrostructuralcharacterizationThemachinedsampleswereinitiallygroundusingdifferentgradesofpolishingpaper,andthenpolishedwith0.25mdiamondpaste.Polishedsampleswereetchedbyanetchantsolutionof5mlaceticacid,10mlH2O,6gpicricacidand100mlethanol.OpticalmicroscopicstudieswerecarriedoutusingLeicaDMRXMicroscopewithQWinimageAnalysissoftware.ThedistributionofPbinthealloywasexaminedinaJEOL,JSE35cscanningelectronmicroscopeSEMattachedwithanenergydispersivespecstereoscopeEDS.铅元素对AZ91镁合金形成过程的影响摘要据调查,AZ91镁合金在形成的过程中至少包含2的微量元素。该结果显示铅物质能抑制化学过程的急剧进行,从而降低化学反应的速度,尽管在同一时间内获得两种合金元素是非常难的。我们只能在400分钟时间内获得铅元素,900分钟时间内获得基本合金。固体铅的存在能抑制铅镁原子的扩散,它的形成是有必要的并且可以抑制反应的急剧形成。关键词AZ91镁合金,铅元素,化学反应,微型机构,数学分析1前言目前,镁合金大量应用于自动控制工业中。多半原因是他们制定了具体的改进方案,这种产品比铅箔或钢制品的质量要轻比铅轻30,比钢轻75。在这许多普通商业的镁合金中,AZ91被认为是最好的化合物,因为它有较强的机械性能及韧性。铅箔的出现使机械和铸造产品具有抗腐蚀性能,同时锌的加入使其强度大大得到加强。固体中含量最大的为镁元素,在437℃时可达到总量的12.7在室温下也可以增加2左右。因此,这种合金的铸件被经过高温加热处理后将研究出机械性能更好、有宝贵价值的资料供人们来参考。经过加热到410℃形成Mg17Al12β,我们需要重新解决镁铸模可以形成同种固体的问题。目前进行的镁合金的化学镀镍方法主要有浸锌法和直接化学镀法。浸锌法是在含焦磷酸盐的锌盐溶液中浸渍后,经氰化镀铜打底,然后进行化学镀。直接化学镀法的预处理包括碱性除油、酸性浸蚀和活化阶段。酸性浸蚀一般采用铬酸盐酸洗活化采用HF溶液。碱洗前处理是为了镁合金表面的油脂。在碱性溶液中,镁合金表面会形成氧化物或氢氧化物,酸洗的目的就是为了去除在镁合金表面形成的疏松的膜。氢氟酸活化是为了在镁合金表面形成比较致密的氟化镁薄膜,形成均一电势的表面9。因此,在高温高压下这种剧烈的反应是不可避免的,可以想办法改善它高温下的产物。它也说明了许多要素的总的特点,像黄金以及一些稀有金属也是在间接反应的过程中形成,不过它们是比较昂贵的。据报道,已经初步研究出铅作用于AZ91镁合金后,铅元素倾向于抑制间接反应,另外铅与黄金和稀有金属相比比较便宜,因此一个详细的论述表明铅加入反应后的重要性。如果长时间的使用AZ91合金,甚至铅可以危机到人的身心健康,不过少量的使用可能没有那么严重,这个试验的过程正在被调查研究。经过困难微型分析,结合显微组织进一步观察热处理的过程中依靠光学显微镜和电子

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