铝挤压机培训资料2.docx

铝挤压机培训资料2.docx

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铝挤压机培训资料2

Chapter2MetallurgicalPrinciples

2.1Introduction

THEEXTENSIVEUSEofmetalsoverthousandsofyears,butinparticularduringtheindustrialage,canbeattributedtotheirspecificproperties.Inadditiontotheirgoodelectricalconductivity—associatedwithgoodthermalconductivity—andvisualproperties,themostimportantarethemechanicalpropertiesandthegoodworkability.Theuseandrangeofapplicationofdifferentmetalsdependsontheseandmanyotherproperties,including,forexample,thecorrosionresistance.However,theproductioncostsalsoplayadecisiverole.

Theseextendfromtheaccessibilityandtheextraction（提炼）oftheore（矿石）,thecostintherefining（精炼、提炼、细化）uptoandincludingthecastingandprocessing.Extrusionissuitableasadeformationprocessindifferentwaysforthedifferentmaterials.Thewell-usedexpression‘extrudability’isawayofexpressingthis.

Knowledgeofdeformationtechnology（术语）aloneisnotsufficienttobeabletounderstandandcontroltheprocessestakingplaceduringextrusion.Thequalityofthebilletmaterials,theprocessestakingplacewithintheextrudedmaterialduringextrusion,andthepropertiesoftheextrudedsectioncanbeunderstoodonlyfromametallurgicalviewpoint.

Thischapter,therefore,explainsthebasicterminologyofmetallurgy—naturallyinthecontextoftheaimsofthisbook—toprovidethetoolsneededbythoseinvolvedinextrusion.Moredetailedexplanationscanbefoundintheliterature.

Thismaterialssciencechapterisconcernedonlywithmetals.Theatomsareheldtogetherbytheso-called“metallicbond（金属键）,”whichdifferentiatesthemfromthenonmetals（covalentbond（共价键）,ionicbond（离子键））.Acharacteristicofthismetallicbondistheeaseofmovementoftheouterelectrons,whicharenolongerattachedtoindividualatomsbutformanelectrongas.Thismobilityoftheelectronsisthereasonforthegoodelectricalconductivityofmetals.

Nonmetalliccrystallinematerialscan,asarule,beextrudedonlywithdifficulty,ifatall.Thereisinsufficientductilityintheworkingrangeoftemperaturesandpressure.Glasswithitsamorphous（非晶的）structureis,however,anexceptionbecauseitsoftensonheating.

Recently,metalandnonmetalcompositematerialshavebeenextruded.Nonmetallicparticlesorfibersareuniformlyembeddedinametallicmatrix（金属晶体）,usuallyartificially,toimprovethemechanicalpropertiesandoftentoreducewear.Thesematerialsarealsodiscussedbrieflyinthischapter.

注释：

metallurgical[ˌmetə'lə:

dʒikl;ˌmetə'lə:

dʒikəl]冶金的，冶金学的

thermalconductivity['θə:

məl,'θə:

ml;'θə:

məl][ˌkɔndʌk'tiviti;ˌkɔndʌk'tivəti]导热性

workability[ˌwə:

kə'biliti;ˌwə:

kə'biləti]加工性

thecorrosionresistance[kə'rəuʒən][ri'zistəns]耐腐蚀性

ore[ɔ:

;əur]矿石

refine[ri'fain]提炼

extrudability[ekstrudə'biliti]可挤压性

terminology[ˌtə:

mi'nɔlədʒi;ˌtə:

mə'nɔlədʒi]术语，术语学

metallicbond[mi'tælik;mə'tælik][bɔnd]金属键

nonmetal[ˌnɔn'metl;ˌnɔn'metəl]非金属

ductility[dʌk'tiliti;dʌk'tiləti]延展性，韧性

amorphousstructure[ə'mɔ:

fəs]['strʌktʃə]非晶结构

embed[im'bed]嵌入

metallicmatrix['meitriks]金属基体

2.2Structure

2.2.1LatticeStructureSinglePhase

Allmetalsconsistofcrystallites（晶粒）（smallcrystals）,thearrangement,size,andshapeofwhicharereferredtoasthestructure.Polishingofmetalspecimensandsuitablemethodsofetchingareusedtorevealthestructure—usuallyunderthemicroscope（Fig.2.1）.

Fig.2.1Thestructureofbrass

Thecrystallitesthatformduringsolidificationfromthemeltchangeduringthecooling.Theyarestretchedbythedeformationandreformbyrecrystallizationafterannealingadeformedmaterial.Theyare,however,alwayscrystalliteswithanorderedlatticestructurethatconstitute（构成）themetal.

Ifametalconsistsofonlyonetypeofcrystallite,ithasasingle-phasestructure.

Theregulararrangementoftheatomsofeachcrystalliteformsthelatticestructure.Thesmallestcomponentofthislatticeisreferredtoastheunitcell.Arealcrystallite,alsocalledagrain,consistsofmanyunitcells（晶胞）arrangeduniformlyinadjacentrowslikebuildingblocks.

Theunitcellsareverysmall.Theedgelength,knownasthelatticeconstant,isoftheorderof

mmsothatacrystallitewithameandiameterof0.1mmcontains

elementarylatticebuildingblocks.

Thelocationofalattice—asimplecubiclatticeisshowninFig.2.2—isdefinedbythedirectionoftheedgesoftheelementarycell.Thisisreferredtoastheorientationofthelattice.Inarealmetalbodyconsistingofnumerouscrystallites,thelattercanbedifferentiatedbytheirorientation,whichisusuallycompletelyrandom.

Fig.2.2Elementarycellinasimplecubiclattice

Fig.2.3Diagramofapolycrystallinestructure

Fig.2.4Themostimportanttypesofmetallatticestructures

Thisisshownschematically（如图示意的）inFig.2.3.Thedifferenttypesofmetallatticeshaveasignificanteffectontheirbehaviorduringdeformation.ThemostimportantlatticestructuresareshowninFig.2.4.Theyareface-centeredcubic（fcc）（面心立方）,body-centeredcubic（bcc）（体心立方）,hexagonal（六方）,andbody-centeredtetragonallattices（体心立方晶格）.Figure2.4alsoshowsthelatticestructureoftheimportantmetalsatroomtemperature.

ThedescriptionofaspacelatticebysurfacesanddirectionisusuallygivenbyMiller’sindices（seetheAppendixtothischapter）.

Inthesolidstatethemetalatomstrytoachievethehighestpackingdensity.Thefccandspecifichexagonallatticespossesthedensestspherical（球形的）packing.Theatomsareassumedtobespheresthatpreferentially（优先的）formthesearrangementswhenshakentogether.Abcclatticehasaspatial（空间的）fillingof68%.Face-centeredcubiclatticesandthehexagonalclose-packedstructurehaveaspatialfillingof78%ofthemaximumpossible.Itisthereforeclearthatthedensityofametaldependsnotonlyontheatomicweightbutalsoonthecrystalstructure.

注释：

lattice['lætis]晶格

phase[feiz]相

crystal['kristl]晶体

etching['etʃiŋ]腐蚀

recrystallization[rɪː'kristəlai'zeiʃən]再结晶

anneal[ə'ni:

l]退火

theunitcell['ju:

nit][sel]晶胞

grain[grein]晶粒

adjacent[ə'dʒeisnt;ə'dʒeisənt]邻近的

simplecubiclattice['simpl]['kju:

bik]['lætis]简单立方晶格

schematically[ski'mætikli;ski'mætikəli]图表式地

face-centeredcubic['kju:

bik]面心立方

body-centeredcubic['kju:

bik]体心立方

hexagonal[hek'sægənəl]六方

body-centeredtetragonal[te'trægənəl]体心正方晶格

spherical['sferikəl;'sferəkəl]球的

preferentially[ˌprefə'renʃl;ˌprefə'renʃəl]优先的

spatial['speiʃəl]空间的

Thesizeandshapeofthecrystallitescanbeinfluencedbycontrolofthesolidificationfromthemeltandbyrecrystallisationduringtheannealingofadeformedmetal.Extremelyfinecrystallitescanhavediameterswellbelow1

andlargegrainsseveralmm.Itisalsopossibletogrowsinglecrystals.Theseareparticularlysuitedforstudyingthebasicsofthedeformationprocessedwithincrystals.Cylindricalspecimensseveralcentimeterslongareproducedforthispurpose.

Fig.2.5Pointtypeoflatticedefect（vacancies,interlatticeatoms,substitutionalandinterstitialforeignatoms）

Fig.2.6Dislocation=linearlatticedefect.（a）Edgedislocation.（b）Screwdislocation

Defect-freeidealcrystalsdonotoccurinpractice.Indeed,specificdefectsarenecessaryforplasticdeformationanddiffusion（扩散）processestooccuratall.ThemostimportanttypesofdefectsareshownschematicallyinFig.2.5and2.6andinclude:

●Vacancies:

Numerouslatticesitesareunoccupied.Thenumberofvacanciesincreasesexponentiallywithtemperature.Intheequilibriumstate,e.g.,inanundeformedaluminumcrystalatroomtemperature,approximatelyoneineverybillionlatticesitesisunoccupied.Incontrast,oneinathousandisunoccupiedjustbelowthemeltingpoint.

●Interstitialatoms:

Inpuremetalsembeddedatomsofthesametypebetweentheregularlatticesites.Inalloysspecificforeignatomsthataresignificantlysmallerthantheatomsofthebaselatticecanbeembeddedintotheinterstitialplaces（e.g.,CandNinFe）.

●Foreignatomsthatsubstitutethebasemetalatoms:

Foreignatoms,particularlythosewithasimilaratomicradiusandwithasimilarlatticestructurecanreplaceatomsofthebasestructure.

●Dislocations:

Stepdislocationsarelinesatwhichanatomicplaneends.Ononesideoftheslipplane—socalledbecausethedislocationlinecanmoveinthisplane—thereisonemorelatticeplanethanontheother（Fig.2.6a）.Inascrewdislocation,thelatticeareasaredisplacedrelativetoeachothersothattheatomsarearrangedaroundthedislocationlinelikeaspiral（螺旋状的）（Fig.2.6b）.Areal,usuallyrandomlycurveddislocationlineinaslipplanecanbeconsideredtoconsistofedgeandscrew（韧型和螺旋型）elements.Thedislocationlineconsistsofaclosedringorendsatagrainboundaryorparticle.Inanundeformedstructure,therecanbeupto1kmofdislocationlines/mm3（dislocationdensity

to

）.

Fig.2.7Grainboundarystructure.（a）Lowangleboundary.（b）Highangleboundary[Alt94,Sch81]

Iftheorientationoftwoadjacentcrystallitesdiffersonlyslightly,thegrainboundarybetweenthemcanbeconsideredtoconsistofdislocationslocatedaboveeachother（lowanglegrainboundary;subgrain-boundary）（Fig.2.7a）.Subgrainsdifferintheirorientationfromeachotherbyonlyafewminutesofarcuptoafewdegrees.Agrainboundarybetweencrystalliteswithverydifferentorientations（largeanglegrainboundary）is,incontrast,aseverelydistortedregionwithdefectsofvarioustypes（Fig.2.7b）.

Twinsrepresentaspecialformofcrystallitesincontactwitheachother.Theirorientationisamirrorimageataplaneboundarysurface（Fig.2.8）.

Fig.2.8Twinnedgrainsandtwinboundary

Ametallicstructurethatconsistsofonlyonetypeofat