MB15镁合金板材超塑性能研究

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1、摘要摘要镁合金具有密度低、比强度高、减振性和电磁屏蔽性好等优点，但是由于它的密排六方晶体结构，室温下用常规的塑性成形方法很难成形复杂零件，从而限制了镁合金的应用。本文根据绝大多数镁合金具有超塑性的特点，研究了轧制态MB15镁合金板材的超塑性变形行为，期望通过超塑成形来弥补这些缺陷，使得镁合金能够真正发挥自己的优势。特别是通过开发镁合金超塑成形/扩散连接(SPF/DB)技术，还可以制造出整体多层构件，进而为镁合金的应用开辟更加宽阔的领域。制定了针对MB15镁合金的热轧制工艺，得到了具有细晶等轴组织的超塑性板材。研究了轧制态MB15镁合金在超塑变

2、形过程中的力学行为，得到了表征超塑性性能的主要参数(应变速率敏感指数m，延伸率6和流动应力。)随变形条件变化的规律，确定了最佳超塑变形温度和应变速率区间。综合分析了轧制态MB15镁合金在超塑变形过程中的微观组织和断口，探讨了镁合金超塑变形机制。在轧制态MB15镁合金最佳超塑变形条件下，采用自行研制的气化剂作为加压介质，进行了两层板波纹零件SPF/DB成形，并对界面组织进行了观察，o研究结果证明，轧制态MB15镁合金板材具有良好的超塑性能，能够通过SPF/DB技术制得合格的波纹零件。关键词镁合金;超塑性;变形机制;超塑成形/扩散连接Abstra

3、ctMagnesiumalloyshaveattractedmanyinvestigators'attentionbecauseoftheirgoodpropertiessuchaslowdensity,highstrength/densityratio,excellentcapacityofdampingandelectromagneticshielding.HoweverthekeyrestrictionofMagnesiumalloysapplicationispoorworkabilitybecauseofhexagonalclose

4、packed(HCP)structure.Itisdifficulttofabricatecomplexpartsbyconventionalplasticformingatroomtemperature.Accordinglyweshouldseekappropriatemeasurestoexpandtheirpracticalapplication.SuperplasticityofMagnesiumalloysshouldbeutilizedtosolvethisproblem.Superplasticforming/diffusio

5、nbonding(SPF/DB)technologycanalsohighlyfabricatemulti-layerparts,whichwilldeveloptheapplicationofMagnesiumalloys.RollingexperimenthasgotsuperplasticMB15sheetwithsmallandequiaxialgains.Themechanicalpropertieswerecarefullyinvestigatedbytensiletests.Theregularityofchiefparamet

6、erssuchasflowstresses，elongation‘andstrainratesensitivitymwassummarizedandoptimalsuperplasticdeformationrangeoftemperaturesandstrainrateswasdetermined.ThemicrostructureaswellasfracturewasanalyzedtoclarifythesuperplasticdeformationmechanismofrolledMB15sheet.TheprincipleofSPF

7、/DBtechnologywithagasificationagentaspressingmediawasintroducedandanewgasificationagentwasdevelopedtofabricatetwo-plycorrugatedpartsofMB15intheoptimaldeformationcondition.Atthemeantime,themicrostructureofdiffusionbondinginterfacewasobservedItisconcludedthattherolledMB15shee

8、texhibitsfavorablesuperplasticityandcansuccessfullyfabricatecorrugatedpartsbySPF/D