铝挤压机培训资料5.docx

铝挤压机培训资料5.docx

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铝挤压机培训资料5

Chapter5ExtrusionofSemifinishedProductsinAluminumAlloys

5.1General

Ofallthematerialsprocessedbyextrusion,aluminumoccupiesthepredominantroleintermsofbothproductionvolumeandvalue.Basedontheannualvolumeofproductionofprimaryandsecondarymetal,aluminumisplaceddirectlyafteriron.Themajorityarealloyed（合金化）toproducewrought（可锻的）alloysandformedintosemifinishedproductsofwhich25%areextruded.Themajorityofallextrusionplants,threequartersinGermany,forexample,processaluminumalloys,465,000tin1995.

Thephysicalmetallurgical（治金的）propertiesofaluminumalloysmakethemparticularlysuitablefortheextrusionofproductsveryclosetothefinishedshapeandwithattractiveproperties.Theface-centeredcubic（fcc）structurewith12slip（滑移）systemscombinedwithahighstacking（堆垛）faultenergyisarequirementforgoodcoldandhotworkability.Corresponding（对应的）tothemeltingpointof660℃,thehot-workingtemperatureofaluminumalloysfallsintherangeof350to550℃,whichcanbeeasilywithstoodbytoolsmadefromsuitablehot-workingsteels.Inthistemperaturerangetheflowstressisreducedtovaluesthatrequirerelativelylowspecificpresspressuresforprocessing.Thenaturaloxide（氧化皮）skingivesaluminumanattractiveappearanceandagoodcorrosionresistanceinthenaturalstate.Increasedsurfaceprotectionisgivenbyanodic（阳极的）oxidation.Aluminumformsage-hardening（时效硬化）alloyswithlow-alloying（低合金）additionsthatcombinegoodhotworkabilitywithahighstrengthafterasimpleheattreatment.

Sectionswithanextensiverangeoffunctionspecificcrosssectionscanbeextrudedwithinnarrowtolerancesfromaluminumalloys.Hollowsectionsintheformofrectangulartubesandhollowengineeringplatesofferahighbendingandtorsional（扭转的）stiffness.

Theselectionoftheextrusionprocessislargelydeterminedbythephysicalmetallurgicalpropertiesofthealuminumalloys.Thehighaffinity（类同）tosteelandthusthetendencytoadheretoallextrusiontoolshastobeincludedinthematerialpropertiesinadditiontolowextrusiontemperatureandthegoodextrusionweldability.

Directhotextrusionwithoutlubrication（润滑）andwithoutashellisusedforthemajorityofextrudedproducts,includingsolidandhollowsectionsfromtheeasilyandmoderatelydifficultalloys.Directextrusioncanbeusedforpracticallytheentirespectrum（系列）ofproducts,fromthesimpleroundbartocomplicatedsectionswithacircumscribingcircleclosetothecontainercrosssection.Flatdiesareusedforsolidsectionsandportholediesforhollowsections.

Indirectextrusioncomesintoconsiderationforcompactcrosssectionsinhard-to-extrudealloys.Coldandhotextrusionwithlubricationofthecontainerandthedieisalsousedforbarsandtubes.

注释:

alloyed[ˈælɔid]合金化

wrough[rɔ:

t]可锻的

metallurgical[,metə'lə:

dʒikl]治金的

stacking（[stækiŋ]堆垛）

corresponding[ˌkɔrisˈpɔndiŋ]对应的

oxide[ˈɔksaid]氧化皮

anodic[æ'nɔdik]阳极的

age-hardening时效硬化

low-alloying低合金

torsional[ˈtɔˈʃənəl]扭转的

affinity[ə’finiti]类同

lubrication[ˌluːbriˈkeiʃən]润滑

spectrum[ˈspektrəm]系列

5.2ExtrusionBehaviorofAluminumAlloys

5.2.1FlowStress

Theextrusiontemperaturerange,theflowstressvariations,andthefrictionacrossthetoolingdeterminetheextrusionbehaviorofaluminumalloys.Alloyandqualityrequirementsdeterminethenecessaryexittemperaturefortheextrudedproductandthetemperaturerangeforthedeformation.Intherange350to550

theflowstressofaluminumalloysisverydependentonthetemperatureandthecomposition.TheincreaseintheflowstresswithincreasingcontentofthemostcommonalloyingelementsisshowninFig.5.1.

Figure5.2showsforsomenon-heat-treatable（不可热处理的）alloysthatreducingthetemperaturebyapproximately100

resultsinanalmostdoublingoftheflowstressprovidingthealloyadditionsstayinsolution（溶液）.

Withage-hardeningalloyssimilartoAl-MgSi1thevariationoftheflowstressisdisplacedbysolutionandprecipitation（沉淀）processesaccordingtothecontentofalloyingelementsinthematrix（基体）.

注释:

non-heat-treatable不可热处理的

solution[səˈlu:

ʃən]溶液

precipitation[priˌsipiˈteiʃən]沉淀

matrix[ˈmeitriks]基体

Fig.5.1Increaseintheflowstressofaluminuminhotworkingwithdifferentalloyingadditions

Fig.5.2Flowstressofsomenon-age-hardeningaluminumalloysasafunctionofthedeformationtemperature（maximumoftheflowcurveintorsiontestswith0.655s-1）

5.2.2FlowProcess

Thealuminumalloysarealmostalwaysextrudedindirectcontactwiththecontaineranddiemanufacturedinhot-workingsteel.However,aluminumexhibitsasignificantchemicalaffinityandadhesiontendencywithiron.Eveninthesolidstateittendstoadheretotoolsurfaces.Atfacepressuresabovetheflowstress,Coulomb’slawsoffrictionlosetheirvalidity（正确性）ifthesheardistortion（扭曲）oftheperipheral（外围的）layerrequireslessforcethantheslipalongthesurfaceoftheharderfrictionalparty.Thefacepressureattheinnerfaceofthecontainerisoftheorderof10timestheflowstress.Therefore,aluminumalloysflowindirectextrusionaccordingtoflowtypeB1asshowninFig.5.3.

注释:

validity[və'liditi]正确性

distortion[dis'tɔ:

ʃən]扭曲

peripheral[pə'rifərəl]外围的

5.2.2.1TheDeadMetalZone

Thebilletsurfaceisstationary（静止不动的）relativetothecontainerinnerwall,andthesheardistortionisatamaximumimmediatelybelowthesurface（Fig.5.4）.

Adeadmetalzoneformsinfrontofthefaceoftheflatdie.Thesurfaceoftheextrudedsectionisnotformedfromthesurfaceofthebilletbutfromtheinteriorofthebilletbyshearingalongthedeadmetalzone.Theoutermostlayerofthebilletsurfaceinitiallyadherestotheinnerwallofthecontainerandisshavedoffbytheadvancingdummyblock（挤压垫块）.Thematerialthatiscompressedtogetherinfrontofthedummyblockandthatcontainsoxideandexudations（渗出物）fromthebilletsurfacesendsupwellbelowthesurfaceoftheextrusionfollowingthepathshowninFig.5.3,No.2,andformsanincompletelybondedintermediate（中间）layerreferredasthepipingdefect.Materiallocatedfartherbelowthesurfaceiscompressedattheupperedgeofthedeadmetalzoneandfollowspath1ofthedeadmetalzoneintotheregionofthesurfaceoftheextrudedproduct.Adhesionofthematerialalsooccursinfeederchambersandintheportsofportholedieswherethereisahighpressure.

Fig.5.3FlowtypesB,B1,andCandtheflowinwardofthebilletperipherallayeralongthedeadmetalzone（path1）andfromthedummyblockedgeintotheinteriorofthebillet（path2）

Fig.5.4Adhesionofthebilletsurfacetothecontainerwallandthesheardeformationoftheperipherallayer

注释：

stationary[ˈsteiʃənəri]静止不动的

dummyblock挤压垫块

exudation[,eksju:

'deiʃən]渗出物

intermediate[ˌintəˈmi:

diət]中间

5.2.2.2IntheShape-ProducingAperture

Thepressureconditionsinthedieaperture（孔）aredifferent.Theaxialpressureattheexitiszero,ortherecanbeasmalltensilestress（拉力）—ifapullerisused.

Thefacepressure,whichdeterminesthefriction,cannotbeeasilycalculatedbecauseitstraddles（跨越）twoboundarycases.Ifthesectioncanslideasasolidbodythroughthedieaperture,thefacepressure,andthusthefriction,islow.Ifthesectionundergoesareductioninthicknessthroughanarrowingdieaperture,thefacepressureisatleastequaltotheflowstress.Thelargeadhesionaffinityofaluminumincreasesthefrictionstresstothesameorderofmagnitudeastheshearstress.

Thefrictioninthedieopeningisresponsiblefortheincreaseintheaxialpressureagainsttheflowdirection.

SlipwithCoulombfriction（库伦摩擦）isimpossibleintheextrusionoftubesoveramandrelbecauseofthehighradialpressurebetweenthebilletandthemandrel.Iftheextrusioniscarriedoutoverastationarymandrel,relativemovementwithshearfrictiontakesplacebetweenthebilletandthemandrelfromthestartofextrusionovertheentirebilletlength.Therelativespeedisthereforeoftheorderofmagnitudeofthestemspeed.Thebilletmaterialisonlyacceleratedtotheexitspeedofthetubeasitcrossesthedeformationzoneandatthesametimethepressureonthemandrelsurfacefallsrapidly.Thetransitiontoslippingfrictionofthefinishextrudedtubeoverthemandreltiptakesplaceintheregionofthedieaperture.

Whenamovingmandrelisused,thezoneinwhichrelativemovementoccursbetweenthebilletandthemovingmandrelisonlythelengthofthedeformationzone.Theshearzonemovestowardthebackofthebilletastheextrusionprogresses.

注释:

aperture[ˈæpətjuə]孔

tensilestress张应力

straddle[ˈstrædl]跨越

coulombfriction['ku:

lɔmˈfrikʃən]库伦摩擦

5.2.3ThermalBalanceandExtrusionSpeed

Inthedirectextrusionofaluminumalloyswithoutlubrication,twotothreetimesthemechanicalworkisneededthanwouldberequiredforanidealloss-freedeformation（无亏损变形）.Theworkcarriedoutbythepressonthematerialbeingextrudedispracticallycompletelytransformedintoheat,whichispartlytransferredintothetoolingandpartlyremovedintheemergingextrusion.Intheadiabaticlimitingcase（绝热极限情况）,eachMPaofaverageextrusionpressurecorrespondstoanaverageincreaseintemperatureof0.3K.

ThemagnitudeinvolvedisshowninFig.5.5forthecaseofaneasilyextrudedmaterialwithaflowstressof25MPainwhichabilletoflengthL0=4D0isextrudedasquicklyaspossiblewithanextrusionratioof30toavoidanyheatlosses.Whenamaterialvolumecorrespondingapproximatelytothevolumeofthedeformationzoneisextruded,thereisinitiallyasteepincreaseintemperature.Withloss-freedeformation,whichapproximatelyoccursinthe