AZ31B镁合金薄板的单向拉伸行为实验研究

在Gleeble-3500热模拟试验机上对AZ31B镁合金薄板(0.6 mm)拉伸试样在100～350℃的温度范围和1×10-1～1×10-3s-1的应变速率范围内进行了的单向拉伸实验,根据实验结果对AZ31B镁合金薄板的力学性能进行了分析.结果表明:AZ31B镁合金薄板在较低变形温度100～150℃时,应变速率对流动应力的影响不大;相比之下应变速率对AZ31B镁合金的断裂伸长率却有一定的影响,提高应变速率会降低材料的伸长率;在较高变形温度(200℃以上)时,应变速率对流动应力的影响比较明显,表现出显著的应变速率敏感性.     

基于3D CA的AZ31镁合金动态再结晶行为研究

本文建立了三维元胞自动机(3D-CA)模型,通过热压缩试验和电子背散射衍表征技术(EBSD),对AZ31镁合金在热变形过程中的微观组织演化规律进行可视化和定量预测。根据试验得出的真应力-应变曲线,确定了3D-CA模型参数在试验条件下的取值,建立了模型参数与变形条件(应变、变形温度和应变速率)之间的关系。利用所建立的3D-CA模型,对AZ31镁合金在热变形过程中的流动行为和微观组织演化进行模拟和讨论。结果表明:再结晶体积分数随着应变的增大而增加,随着变形温度的增大或应变速率降低而增大,提高应变速率或降低温度可以细化再结晶晶粒。模拟结果与实验结果吻合较好,相对误差值在4.5%-16.2%之间,所建立的3D-CA模型能够较准确地预测镁合金AZ31的微观组织演化。     

High strain rate superplasticity of rolled AZ91 magnesium alloy

The high strain rate superplastic deformation properties and characteristics of a rolled AZ91 magnesium alloy at temperatures ranging from 623 to 698 K（0.67Tm-0.76Tm） and high strain rates ranging from 10^-3 to 1 s^-1 were investigated.The rolled AZ91 magnesium alloy possesses excellent superplasticity with the maximum elongation of 455% at 623 K and a strain rate of 10-3 s-1,and its strain rate sensitivity m is high up to 0.64.The dominant deformation mechanism responsible for the high strain rate superplasticity is still grain boundary sliding（GBS）,and the dislocation creep mechanism is considered as the main accommodation mechanism.     

Flow stress and microstructural evolution in as rolled AZ91 alloy during hot deformation

1　INTRODUCTIONMgalloysarethelightestconstructionmaterialsformanyengineeringcomponentsduetotheirlowdensity ,higherductilityandsuitablestrength[13] .However ,Mgalloyshavepoorformabilityandlimit edductilityatroomtemperaturebecauseofitsHCPstructure[4 ] .Therefore ,itisrequiredforMgalloystobedeformedatwarmtemperature(>4 98K ) [5] ,es peciallyatelevatedtemperature ,whenprismaticslipisactivatedsothattheformalityofMgalloyscanbeimprovedintermsofhighductilityandmakesiteasytosimplifythedesignandm…     

Deformation Mechanism and Hot Workability of Extruded Magnesium Alloy AZ31

Using the flow stress curves obtained by Gleeble thermo-mechanical testing, the processing map of extruded magnesium alloy AZ31 was established to analyze the hot workability. Stress exponent and activation energy were calculated to characterize the deformation mechanism. Then, the effects of hot deformation parameters on deformation mechanism,microstructure evolution and hot workability of AZ31 alloy were discussed. With increasing deformation temperature, the operation of non-basal slip systems and full development of dynamic recrystallization(DRX) contribute to effective improvement in hot workability of AZ31 alloy. The influences of strain rate and strain are complex. When temperature exceeds 350 °C, the deformation mechanism is slightly dependent of the strain rate or strain. The dominant mechanism is dislocation cross-slip, which favors DRX nucleation and grain growth and thus leads to good plasticity. At low temperature(below 350 °C), the deformation mechanism is sensitive to strain and strain rate. Both the dominant deformation mechanism and inadequate development of DRX deteriorate the ductility of AZ31 alloy. The flow instability mainly occurs in the vicinity of 250 °C and 1 s-1.     

Hot-compression constitutive relation of as-cast AZ31 magnesium alloy

In hot-compression process, the various factors have obvious effects on the deformation behavior of AZ31 magnesium alloy deformation behavior. To understand the hot-compression constitutive relation thoroughly, the stress-strain behavior of AZ31 magnesium alloy at various strain rates and different deformation temperatures were investigated under maximum strain of 60%. The microstructure of the experimental alloy was studied in the hot-compression procedure. The experimental results show that the relation of peak flow stress, strain rate and temperature can be described by Z parameter which contains Arrheniues item. The strain rate and the deformation temperature are the key parameters affecting deformation activation energy.     

AZ31镁合金铸轧和常规轧制板的变形组织及形变特征

在变形温度为150～400 ℃、应变速率为0.3～0.000 3 s~(-1)条件下,在Gleeble1500热模拟机上采用等温拉伸试验对AZ31镁合金铸轧和常规轧制板的高温塑性及组织演变进行研究.结果表明:两种AZ31镁合金板的峰值应力和峰值应变均随着变形温度的降低和应变速率的增加而逐渐增大.铸轧板的应变硬化指数和应变速率敏感系数均大于常规轧制板的.在高温低应变速率变形条件下,铸轧板的晶界滑移引起的空洞尺寸、体积分数和密度均大于常规轧制板的.低应变速率下拉伸变形后的动态再结晶晶粒尺寸随温度的升高逐渐增加;不同变形条件下铸轧板的晶粒尺寸均小于常规轧制板的;再结晶晶粒尺寸和Z参数呈幂律关系.     

AZ31镁合金热变形流动应力预测模型

采用近等温单轴压缩实验获得了AZ3l镁合金变形温度为523 723 K,应变速率为0.01—10 s^-1条件下的流动应力,分析了变形温度和应变速率对流动应力的影响规律.结果表明,AZ31镁合金变形过程中发生了动态再结晶,523 K时形成细小组织;而723 K时动态再结晶和长大的晶粒沿径向拉长.考虑实验过程塑性变形功和摩擦功引起的温度升高,在高应变速率条件下采用温度补偿修正了流动应力.在此基础上,建立了基于双曲正弦模型的峰值流动应力和统一本构关系,该模型利用材料参数耦合应变来描述流动应力的应变敏感性,进一步获得了合金热变形过程中流动应力与变形温度、应变速率和应变的定量关系.采用该本构关系模型预测流动应力具有较高的精度,预测值与实测值相关系数为0.976,平均相对误差为5.07%,实验条件范围内预测的流动应力与实验值几乎能保持一致.     

AZ31铸造镁合金的塑性流动特征及物理概念的本构关系

利用准静态试验机以及Hopkinson压杆装置对AZ31铸造镁合金在不同应变速率和不同温度下的塑性流动性能进行研究,结合金相显微技术对试验后的试样进行微观分析。结果表明:在低应变速率下,随着温度的升高,AZ31镁合金发生明显的由脆性到韧性的转化,其转化温度为473 K左右;当应变速率增加到1.2×104 s-1时,会发生脆化现象,塑性变形能力变差。基于微观分析,低应变速率下晶体中孪晶的存在是促进材料塑性变形增加的主要因素。而在高应变速率下,动态再结晶和第二相粒子沉淀硬化显著地影响金属的塑性变形。结合系统的试验结果,基于热激活位错机制,建立一种物理概念的塑性流动本构模型,对较高应变速率和不同温度下的流动应力进行模型预测。通过对比,模型预测结果与试验数据吻合较好。     

AZ31B镁合金热压缩变形的组织变化与变形机制

对铸态AZ31B镁合金在温度280℃～440℃、应变速率0.001s-1～0.1s-1条件下进行热压缩实验,分析变形程度、应变速率和加热温度对其微观组织变化的影响,探讨合金的热压变形机制。实验结果表明,该合金热变形时发生了动态再结晶。变形温度越高、变形速率越小和变形量越大时,动态再结晶进行的越充分;变形温度越低、变形速率越大和变形量越大时,动态再结晶晶粒越细小。该合金的热变形机制是滑移孪晶联合机制。     

AZ80合金高温变形行为及加工图

为实现AZ80合金塑性成形的数值模拟和制定其合理的热加工工艺,利用热模拟机对AZ80合金进行不同变形温度和应变速率的高温压缩变形行为研究.结果表明:AZ80合金的高温流动应力-应变曲线主要以动态回复和动态再结晶软化机制为特征,峰值应力随变形温度的降低或应变速率的升高而增加;在真应力-应变曲线基础上,建立的AZ80合金高温变形的本构模型较好地表征其高温流变特性,模型计算精度高;同时,利用建立的AZ80合金的DMM加工图分析其变形机制和失稳机制,从提高零件力学性能角度考虑,可以优先选择变形温度为300～350 ℃、应变速率为0.001～0.01 s-1的工艺参数.     

受力方式和变形速度对AZ31挤压板材平面应变过程中孪生的影响

采用X射线衍射、断口扫描、金相观察、应力-应变曲线等分析手段,通过对AZ31镁合金挤压板材在室温下的平面应变试验,研究了不同受力方式和不同变形速度对孪生产生的影响。结果表明,N向拉伸变形以{1012}孪生为主;N向压缩变形仅在变形末期在少量具有有利取向的晶粒内发生孪生;N向限制变形中,变形初期发生{1012}孪生变形,随着变形程度的增加,孪生停止。变形速度影响孪晶的形核和长大。当主要变形机制为孪生时,变形速度越慢,越有利于孪晶的形核与长大,提高材料的强度和塑性。     

铸造Mg-4Al-2Sn-Y-Nd镁合金的热压缩行为与加工图

利用热压缩实验研究一种新型的具有优异室温塑性的Mg-4Al-2Sn-Y-Nd镁合金的高温流变行为,变形温度为200～400℃,应变速率为1.5×10-3～7.5 s^-1。结果表明：合金的应变速率敏感因子（m）在不同变形温度下均明显小于AZ31镁合金的m值,因此该合金适合在高应变速率下进行热加工。在真应力-应变曲线基础上,建立Mg-4Al-2Sn-Y-Nd 镁合金高温变形的本构方程,并计算得到合金的应力指数为10.33,表明合金在高温下主要的变形机制为位错攀移机制。同时,利用加工图技术确定合金的最佳高温变形加工窗口,即变形温度在350～400℃之间,应变速率在0.01～0.03 s^-1。     

退火工艺对高温叠轧AZ31镁合金板材组织与性能的影响

将高温叠轧变形和退火再结晶相结合,尝试共同调控AZ31镁合金板材的组织与织构。在300℃下对高温叠轧AZ31镁合金板材进行不同时间的退火处理,并研究了退火对高温叠轧板材组织、晶粒取向和力学性能的影响。结果表明:随退火时间的增加,界面结合质量逐渐提高,当退火时间为30 min时,部分区域出现冶金现象;显微硬度随退火时间的增加而降低;延长退火时间,高温叠轧板材非基面取向晶粒比重显著增加,同时,高温叠轧历史累积应变量、后续退火两者共同作用促使AZ31镁合金板材基面织构显著弱化。     

An Experiment on Magnetic Pulse Uniaxial Tension of AZ31 Magnesium Alloy Sheet at Room Temperature

Formability of magnesium alloys at room temperature or slightly elevated temperatures is low, and exhibiting poor resistance to strain localization and failure. However, it is possible to improve the formability of AZ31 magnesium alloy sheet at high strain rate such as by electromagnetic forming (or magnetic pulse forming). In this study, experimental investigation of uniaxial tension of AZ31 sheet by magnetic pulse forming at room temperature was presented. The approximate rectangular flat spiral coil was employed to carry out the experiments. The specimens used in the tension test by magnetic pulse forming were same as the quasi-static uniaxial test. The samples were placed close to the outside of coil where an approximately homogenous magnetic field distribution prevailed. The experimental results indicate that the total elongation of AZ31 sheet improves about 37% compared with the quasi-static case. Non-uniform deformation occurs in the specimen. The maximum strain takes place on the area C, where is plotted on the specimen. The major and minor principal strains at most increase by approximately 112 and 96% under 5.12 kJ energy. The experimental results obtained in this study provide the fundamentals for the investigation of high speed forming of AZ31 magnesium alloy sheets.     

AZ80镁合金变形特性及管材挤压数值模拟研究

利用Gleeble热模拟机研究了AZ80合金的高温变形特性。结果表明,流变应力取决于变形温度和变形速率。当应变速率一定时,流变应力随变形温度的升高而降低;当温度一定时,流变应力随着应变速率的升高而增大。根据AZ80镁合金真应力-真应变曲线,建立了其流变应力模型。采用刚塑性有限元法对AZ80镁合金管材挤压过程进行热力耦合数值模拟,并分析了高温挤压成形过程中变形力及金属流动规律,着重探讨了变形温度和挤压速度等挤压工艺参数对挤压力、应变场以及应力场的分布及变化情况的影响。模拟的结果为AZ80镁合金管材挤压工艺参数的制定、优化提供了科学依据。     

Characteristics of hot tensile deformation and microstructure evolution of twin-roll cast AZ31B magnesium alloys

High temperature tensile properties and microstructure evolutions of twin-roll-cast AZ31B magnesium alloy were investigated over a strain rate range from 10-3 to 1 s-1.It is suggested that the dominant deformation mechanism in the lower strain rate regimes is dislocation creep controlled by grain boundary diffusion at lower temperature and by lattice diffusion at higher temperatures,respectively.Furthermore,dislocation glide and twinning are dominant deformation mechanisms at higher strain-rate.The processing map,the effective diffusion coefficient and activation energy map of the alloy were established.The relations of microstructure evolutions to the transition temperature of dominant diffusion process,the activation energy platform and the occurrence of the full dynamic recrystallization with the maximum peak efficiency were analyzed.It is revealed that the optimum conditions for thermo-mechanical processing of the alloy are at a temperature range from 553 to 593 K,and a strain rate range from 7×10-3 to 2×10-3 s-1.     

AZ31镁合金位错密度模型及热压缩的微观组织预测

通过热压缩实验研究AZ31镁合金挤压杆料在变形温度300、400和500℃,应变速率0.1、0.01和0.001 s^?1条件下的流变行为,基于Arrhenius方程建立流变应力的本构模型,其中激活能Q为132.45 kJ/mol,应变硬化系数n为4.67。依据AZ31镁合金高温变形中的动态再结晶(Dynamic recrystallization,DRX)机理和位错密度演化规律,建立宏观变形?微观组织多尺度耦合的位错密度模型,该模型能够反映热加工过程中的加工硬化、动态回复(Dynamic recovery,DRV)、低角晶界(Low angle grain boundaries,LAGB)和高角晶界(High angle grain boundaries,HAGB)等机制的交互作用。利用ABAQUS的VUSDFLD子程序进行热压缩过程的有限元模拟,获得DRX分数、LAGB和HAGB位错密度的数值模拟结果以及压缩载荷。结果表明:实验载荷与模拟结果基本吻合,本文提出的AZ31镁合金位错密度模型是合理的。     

Analysis on flow stress of magnesium alloys during high temperature deformation

The flow stress of magnesium alloys during hot compression at different temperatures and strain rates was studied by experiments.Materials used were AZ91D alloys in as-cast,homogeneous treatment states,AZ31 and ZK60 alloys in as-cast state. The results show that the thermal simulation curves of different alloys differ from one another at the same deforming condition.The general curves of AZ31 and AZ91D alloys have the character of dynamic recrystallization.There are increase of true stress,drastic fallin...     

Flow stress and softening behavior of wrought magnesium alloy AZ31B at elevated temperature

1　INTRODUCTIONThewroughtmagnesiumalloyshaveexcellentspecificstrengthandstiffness ,machinability ,dampcapacity ,dimensionalstability ,lowmeltingcostsandare ,hence ,veryattractiveinsuchapplicationsasau tomobile ,aviation ,electronicandcommunicationin dustry[16 ] .Investigationsontheflowstressandsofteningbehaviorofmagnesiumalloysathigherformingtem peratureandstrainratehavebeenanimportantsub jectinwroughtmagnesiumalloysforming[710 ] .InthispapertheflowstressandsofteningbehaviorofAZ31Bdeform…