AZ31镁合金细管挤压工艺及组织性能分析

硕士学位论文AZ31镁合金细管挤压工艺及组织性能分析STUDYONMICROSTRUCTUREANDPROPERTIESOFTHINTUBEOFAZ31MAGNESIUMALLOYBYEXTRUSIONTECHNOLOGY姜轶群哈尔滨工业大学2012年7月国内图书分类号：TG379学校代码：10213国际图书分类号：621密级：公开工学硕士学位论文AZ31镁合金细管挤压工艺及组织性能分析硕士研究生：姜轶群导师：于洋副教授申请学位：工学硕士学科：材料加工工程所在单位：材料科学与工程学院答辩日期：2012年7月授予学位单位：哈尔滨工业大学ClassifiedIndex:TG379U.D.C:621DissertationfortheMasterDegreeinEngineeringSTUDYONMICROSTRUCTUREANDPROPERTIESOFTHINTUBEOFAZ31MAGNESIUMALLOYBYEXTRUSIONTECHNOLOGYCandidate：JiangYiqunSupervisor：AssociateProf.YuYangAcademicDegreeAppliedfor：MasterofEngineeringSpeciality：MaterialProcessingEngineeringAffiliation：SchoolofMaterialsScienceandEngineeringDateofDefence：July,2012Degree-Conferring-Institution：HarbinInstituteofTechnology哈尔滨工业大学工学硕士学位论文摘要镁合金由于其良好的生物相容性、可降解性和优良的机械性能，而展现出在现代介入医疗器械应用领域极大优越性。本文研究一种镁合金毛细管低温挤压成形新技术，揭示其低温挤压塑性变形机理并系统研究变形规律，为镁合金细管塑性加工的应用奠定理论和技术基础，并且开发出一种尺寸精度高的高强韧镁合金毛细管新型材料，能够实现镁合金组织性能及精密成形控制一体化，对于拓展微尺寸高强韧镁合金应用领域具有重要意义，并昀终获得细微管材的制造新技术。本文以AZ31镁合金为研究对象，采用空心锭正向挤压成形工艺，进行了较为系统的挤压实验研究。确定了挤压成形的工艺参数，并在实验过程中不断优化工艺参数，以实现AZ31镁合金细管的挤压成形，并且通过金相显微镜和电子万能试验机、维氏显微硬度计等设备进行了分析实验，分析了空心锭正向挤压法制备的管材壁厚的均匀性，研究了在不同的挤压工艺过程中，不同的挤压温度和挤压比等参数对AZ31镁合金晶粒大小和性能的影响以及热处理的时间对镁合金晶粒大小和性能的影响。研究结果表明：在实验所确定的工艺参数下采用空心锭正向挤压成形工艺挤压出的管材壁厚比较均匀，壁差率从管材头部向管材尾部逐渐减小，尾部壁差率昀小为2.5%。管材的表面没有裂纹、分层、凹陷等缺陷，而且表面的粗糙度和尺寸的精度都比较好。第一次挤压时，发生了动态再结晶，晶粒明显细化，只是动态再结晶进行的不完全。第二次挤压时，进行了充分的动态再结晶，晶粒大小均匀，只是晶粒有所长大。随着挤压时坯料温度的升高，晶粒逐渐增大，硬度和抗压强度逐渐减小。对于Φ8mm×1mm的管材，模具预热温度均为300℃，第一次挤压时坯料温度为200℃，第二次挤压时坯料温度为150℃时性能较好。随着挤压比的增大，晶粒细化效果越来越显著，晶粒逐渐减小，硬度和抗拉强度逐渐增大。对于外径≤4.1mm的管材，挤压比为31.5时性能较好。热处理后管材发生了回复再结晶，晶粒大小比较均匀。随着退火保温时间的延长，晶粒有所长大，管材的抗压强度以及硬度逐渐减小，尤其是在225℃保温120min时出现了异常长大的晶粒，抗压强度和硬度大幅度降低；随着退火温度的升高，晶粒几乎没有长大，管材的抗压强度和硬度相差不多。225℃保温30min时得到的管材性能比较好。关键词：AZ31镁合金；细管；挤压；组织性能-I-哈尔滨工业大学工学硕士学位论文AbstractMagnesiumalloyownsmanyexcellentpropertiessuchasbiocompatibility,degradableandmechanicalproperties.Inthemodernmedicalequipmentapplicationfield,magnesiumalloyhasgreatsuperiority.Thispaperstudiesanewcapillaryextrusiontechnologythatismagnesiumalloylowtemperatureextrusion.Thistechnologyrevealstheplasticdeformationmechanismoflowtemperatureandresearchesthedeformationlawssystematically.Laythefoundationsforthetheoriesandtechnologiesontheplasticprocessingapplicationofmagnesiumalloythintube.Developanewmaterialformagnesiumalloycapillary.Thematerialhashighdimensionaccuracy,strengthandtoughness.Itcanrealizeintegratedcontrolfortheorganizationandpropertyofmagnesiumalloyandprecisionforming.Ithasimportantmeaningsforexpandingapplicationfieldofmagnesiumalloywhichhastinysize,highstrengthandtoughness.Finallywecanobtainanewmanufacturetechnologyoftinytubes.ThispaperstudiedonAZ31magnesiumalloyandusedaformingtechnologyofhollowingotpositiveextrusion.Thestudiesofextrusionexperimentswererelativelysystematical.Gotthetechnologyparametersofextrusionformingandoptimizedtheprocessparameterscontinuouslythroughexperiments.RealizedthintubesextrusionformingofAZ31magnesiumalloy.Thispaperanalyzedtheexperimentresultsthroughtheequipmentsofmetallographicmicroscope,electronicuniversaltestmachineandVickersmicro-hardnessgauge.Andanalyzeduniformityoftubewallthicknesswhichmadebyhollowingotpositiveextrusion.ItalsostudiedthatheattreatmenttimeanddifferentextrusionparameterssuchasextrusiontemperaturesandtheratioofextrusionhowtoinfluenceAZ31magnesiumalloygrainsizesandtheproperties.Theresultsshowedthat:tubewallthicknesswasrelativelyuniformwhenextrudedbyhollowingotpositiveextrusionwiththedefinedprocessparameters.Theratioofwallmarginreducedgraduallyfromtheheadtotheend.Theminimumoftheratioofwallmarginis2.5%.Thesurfaceoftubesdidn’thavedefectsofcracks,layersanddepressions.Theroughnessofthesurfaceandtheprecisionofthedimensionarequitegood.Thedynamicrecrystallizationhappenedandgrainsizewasrefinedatthefirstextrusionprocess,butdynamicrecrystallizationhappenedincompletely.Thedynamicrecrystallizationcompletelyhappenedatthesecondextrusionprocessandgrainsizeuniform,butgrainsizegrewupslightly.Alongwiththeriseofblanktemperature,thegrainsizeincreasedgraduallyreduced,strengthandhardnessreducedgradually.Theresultsshowedthatundertheconditionsofmouldpreheatingtemperatureat300℃,thefirstblanktemperatureat200-II-哈尔滨工业大学工学硕士学位论文-III-℃andthesecondblanktemperatureat150℃,tubesofΦ8mm×1mmcouldobtainoptimalcomprehensiveproperties.Alongwiththeriseofextrusionratio,theeffectoffine-grainstrengtheningwasmoreobvious.Notonlygrainsizesgraduallyreducedbutalsocomprehensivepropertiesgraduallyincreased.Theresultsalsoshowedthattubeswhoseoutsidediameterlessthanorequalto4.1mmandextrusionratiois31.5couldobtainoptimalcomprehensiveproperties.Thestaticrecrystallizationoccurredintheheattreatmentprocess,grainsizeswereuniformrelatively.Alongwiththeextensionoftheannealingheatpreservationtime,notonlygrainsizesgrewup,butalsothecompressivestrengthandthehardnessoftubesgraduallyreduced.Especially,grainsizesgrewupabnormallyandthecompressivestrengthandhardnessgreatlyreducedwhentheannealingheatpreservationtimewas120min.Alongwiththeannealingtemperatureincreased,grainsalmostnotgrewupandsothecompressivestrengthandthehardnessoftubes.Thetubesachievedbetterproperties