铝合金铸造工艺性能Aluminum alloy casting process performanceWord文档下载推荐.docx

铝合金铸造工艺性能Aluminum alloy casting process performanceWord文档下载推荐.docx

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（1）liquidity

Liquidityistheabilityofthealloyliquidtofillcasting.Theamountofliquiditydetermineswhetherthealloycancastcomplexcastings.Itisbesttobeliquidinaluminumalloy.

Therearemanyinfluencefactorsinliquidity,mainlyexistinthecomposition,temperature,andalloyliquidmetaloxides,metalcompoundsandotherpollutantsofsolidphasedparticles,buttherootoftheexternalfactorsforthepouringtemperatureandpouringpressure（commonlyknownaspouringhead）.

（2）systolic

Contractibilityisoneofthemaincharacteristicsofcastaluminumalloy.Generallyspeaking,thealloyismadefromliquidtosolidifieduntilitiscoldtoroomtemperature,whichisdividedintothreestages,whichareliquidshrinkage,solidificationcontractionandsolidcontraction.Thecontractionofalloyhasadecisiveinfluenceoncastingquality,whichaffectsthesizeofshrinkagecavity,theproductionofstress,theformationofcrackandthechangeofsize.Theshrinkageofthecastingisusuallydividedintocontractionandcontractionofthebody,andthecontractionofthealloyismeasuredintheactualproduction.

Aluminumalloyshrinkage,usuallyexpressedasapercentage,iscalledshrinkage.

（1）bodycontraction

Thecontractionofthebodyincludesthecontractionoftheliquidandthecontractionofsolidification.

Castingalloyliquidfromcastingtosolidification,canappearinthelastsolidificationplacemacroscopicormicroscopicshrinkage,themacroscopicshrinkagecavitycausedbyshrinkagevisibletothenakedeye,andcanbedividedintocentralizedshrinkagecavityanddispersionshrinkagecavity.Theporediameteroftheconcentratedshrinkagecavityislargeandconcentrated,andisdistributedinthehotsectionofthetoporsectionofthecasting.Thedispersionoftheshrinkagecavityisdispersedandsmall,mostlyinthecastingaxisandthehotsection.Themicroscopicshrinkagecavityisnotvisibletothenakedeye,andthemicroshrinkagecavityismostlydistributedinthecrystalboundaryordendritebranches.

Shrinkagecavityandporosityareoneofthemaindefectsofcastings.Foundinproduction,castingaluminiumalloysolidificationrangeissmaller,theformationofconcentratedshrinkage,solidificationrangeiswide,themoreeasydispersionshrinkagecavityformation,therefore,inthedesignmustconformtotheprincipleofdirectionalsolidificationcastingaluminumalloy,thecastingliquidistothebodyduringthesolidificationshrinkageshouldbealloyliquidsupplement,isloosefocusontheoutsideofthecastingsandshrinkagecavityatthemouth.Foreasygenerationdispersedporousaluminumalloycastings,muchlargerthantherisersetnumberconcentrationofshrinkagecavity,andinasettingarepronetoloosecoldiron,increasinglocalcoolingspeed,makeitsorrapidsolidificationatthesametime.

（2）thelinearshrinkage

Lineshrinkagewilldirectlyaffectthequalityofcasting.Thelargerthelinecontraction,themorethetendencytocrackandstressinaluminumcastings;

Aftercooling,thesizeandshapeofthecastingsalsochanged.

Fordifferentcastingaluminumalloy,theshrinkagerateofcastingisdifferent,evenifthesamealloy,castingisdifferent,theshrinkagerateisdifferent,andtheshrinkagerateofitslength,widthandheightisdifferentinthesamecasting.Itshouldbebasedonspecificcircumstances.

（3）thethermalcrackingresistance

Theproductionofaluminumcastinghotcrack,ismainlyduetothecastingshrinkagestressthanthebindingforcebetweenthemetalgrain,mostlyfromthefracturesurfaceobservationvisiblecracksalongthegrainboundaryinmetalisoftenoxidation,metallicluster.Thecrackiselongatedalongthegrainboundary,theshapeisserrated,thesurfaceiswider,theinteriorisnarrower,andsomepenetratetheendfaceofthewholecasting.

Aluminumalloycastingcracktendencyisalsodifferent,thisisbecausethecastaluminumalloysolidificationprocessbegintoformacompleteframeworkofcrystallizationtemperatureandsettingtemperature,thegreaterthedifferencebetweenthealloyshrinkagerateis,thegreatertheproducehotcrackingtendencyare,thegreatertheeventhesamekindofalloyduetothestructureoftheresistanceofthecasting,casting,pouringprocessfactorssuchashotcrackingtendencyarealsodifferent.Itisoftenusedtoreducethecastingofaluminumcasting,orimprovecastingsystemofcastingaluminumalloy.Thermalcrackingofaluminumcastingisusuallydetectedbythermalcracking.

（4）theairtightness

Theairtightnessofaluminumalloyisthedegreeofnon-seepageofthealuminumcastinginthecavityofthecavity.Theairtightnessactuallyrepresentsthedegreeofdensityandpurityoftheinnerstructureofthecastings.

Theairtightnessofthecastaluminumalloyisrelatedtothepropertiesofthealloy.Thesmallerthesolidificationrangeofthealloy,thesmallertheloosetendencyandthesmallerthedepositionporosity,thehighertheairtightnessofthealloy.Airtightnessofthesamekindofcastaluminumalloyisgoodorbad,butalsorelatedtothecastingprocess,suchasthelowercastaluminumalloypouringtemperature,putcoldironinordertospeedupthecoolingandsolidificationunderpressure,etc.,allcanincreasethetightnessofaluminumcastings.Itcanalsobeusedtoplugtheleakagegaptoimprovetheairtightnessofthecasting.

Castingstress

Thecastingstressincludesthermalstress,phasechangestressandcontractionstress.Therearedifferentreasonsforstress.

（1）thermalstress

Thethermalstressiscausedbytheuneventhicknessofthedifferentgeometricalshapesofthecastingsandthecoolinginconsistencies.Thestressisformedatthethinwall,resultinginresidualstressinthecastings.

Phasevaryingstress

Thephasechangestressisduetothephasechangeinthecoolingprocessofsomecastaluminumalloyaftersolidification,resultinginthechangeofvolumesize.Itismainlythatthewallthicknessofaluminumcastingisnotuniform,anddifferentpartsofthecastarecausedbyphasechangeindifferenttime.

Contractionstress

Theshrinkageofaluminumcastingiscausedbycastingandcoreblocking.Thisstressistemporaryandaluminumcastingisautomaticallyremoved.However,theimproperopeningtimeoftenresultsinhotcracks,especiallythemetalcastingaluminumalloytendstoproducehotcracksundersuchstress.

Theresidualstressinthecastaluminumalloypartsreducesthemechanicalpropertiesofthealloyandaffectsthemachiningaccuracyofthecasting.Residualstressinaluminumcastingcanbeeliminatedbyannealing.Thealloyhasnophasechangeduetogoodthermalconductivity,aslongasthecastingstructureisreasonable,theresidualstressofaluminumcastingisgenerallysmall.

（6）inspiratorysex

Aluminumalloyiseasytoabsorbgasandisthemaincharacteristicofcastingaluminumalloy.Thecompositionofliquidaluminiumandaluminumalloy,thecombustionproductsoforganicmaterialsandthecombustionproductsoforganicmaterialsandthereactionofthewaterinthemoldcontainingwaterareabsorbedbythealuminumliquid.

Thehigherthetemperatureofthemoltenmetal,themorehydrogenitabsorbs;

At700℃,

Thesolubilityofhydrogeninthealuminumper100gis0.5~0.9,whenthetemperatureto850℃,thesolubilityofhydrogenincreases2~3times.Whenthealkalimetalimpurities,thesolubilityofhydrogeninaluminumisincreasedsignificantly.

Castaluminumalloyinadditiontothemeltinginspiratory,alsoproducesinspiratorywhenpouringintothemold,theliquidmetalintothemoldwiththetemperaturedrop,thesolubilityofagasfell,theprecipitateexcessgas,somefromoutofthegasincastingporosity,whichisusuallycalled"

pinhole"

.Thegasissometimescombinedwitharetracer,andthegasinthealuminumliquidremainsintheshrinkagecavity.Ifthepressureofbubblesisverylarge,theporesaresmooth,andthereisaringoflightaroundthehole.Ifthepressureofthebubbleissmall,theinnersurfaceoftheholeiswrinkled,anditlookslike"

flyfoot"

.

Thehigherthehydrogencontentinthealuminumalloyliquid,themorepinholesproducedinthecasting.Theneedleholesinaluminumcastingsnotonlyreducetheairtightnessandcorrosionresistanceofthecastings,butalsoreducethemechanicalpropertiesofthealloy.Inordertoobtainthealuminumcastingswithoutporosityorporosity,thekeyisthesmeltingconditions.Ifthecoatingagentisaddedtothesmeltingprocess,theinhalationofthealloyisgreatlyreduced.Thealuminummeltliquidisrefined,anditcancontroltheamountofhydrogencontainedinaluminumliquid.

Sandcasting

Moldcastingismadeofsand,clayandotherauxiliarymaterials.Sand-typematerialiscollectivelyreferredtoasmoldingmaterial.Thesandtypeofnon-ferrousmetalismadefromsand,clayorotherbinderandwater.

Aluminumcastingprocessistheprocessofmetalandcastinteraction.Thealuminumalloyfluidisinjectedintothecastmould,andtheheatofthemoltenmetalis