Deformation behavior ofAZ31 magnesium alloy at different strain rates and temperatures

The deformation behavior of AZ31 was examined by compression and tension testes over a wide strain rate and temperature range, strain rate from 10^-3 to 10^3 s^-1, temperature from 300 to 623 K. Analysis of flow behavior and microstructural observations indicate that in tension tests dislocation glide is the most important deformation mechanism in the test strain rate and temperature range, while in compression tests twinning deformation mechanism is important at lower temperature when the strain rate ranges from 10^-3 to 10 s^-1. At 10^3 s^-1 strain rate, dislocation glide and twinning are present at the same time. At the strain rate of 2 964 s^-1, adiabatic shear band can be found easily, even at the strain rate of 1 537 s^-1 adiabatic shear localization zone can be found. In adiabatic shear localization zone, there are fine recrystallization grains. But in adiabatic shear band, the grains cannot be identified by optical microscopy.     

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。     

Low cycle fatigue properties and cyclic deformation behavior of as-extruded AZ31 magnesium alloy

The low cycle fatigue(LCF)properties of as-extruded AZ31 Mg alloy were investigated under total strain amplitudes in the range of 0.4%-1.2%with strain rate of 1×10- 2s -1.Due to the twinning effect in compression during loading and the detwinning effect during unloading,the alloy showed an asymmetric hysteresis loop.The cyclic stress response exhibited cyclic hardening at high total strain amplitudes.The cyclic deformation behaviors were discussed using the Coffin-Manson plot,which divided the plastic strain amplitudes into the tension side and the compression side.Through the LCF tests that were started from either tension or compression under a total strain amplitude of 1.0%,the interaction between the twinning effect and dislocation was analyzed.The twinning effect during the LCF test and the variation of the dislocation density were investigated using optical microscopy and transmission electron microscopy,respectively.     

挤压AZ31B镁合金的低周疲劳性能(英文)

通过外加总应变幅控制的拉-压对称疲劳试验,研究常温下挤压AZ31B镁合金在不同应变幅下的疲劳性能。结果表明,除了在低应变幅0.5%外,样品均呈现循环应变硬化;应变幅为0.5%时,样品在初始阶段呈现循环硬化,随后保持应力恒定;在压缩过程中孪晶的产生以及随后的卸载和反向拉伸过程中的去孪晶行为导致了高应变幅下的滞回环形状拉-压不对称现象,而低应变幅0.5%下的滞回环形状基本对称,说明低应变幅下孪生-去孪生现象不明显。在整个疲劳过程中,高应变和低应变下的应力—应变曲线呈现2种不同的滞回环形状,这是由不同疲劳阶段孪生和位错滑移2种不同的变形机制所导致。     

AZ31镁合金高温热压缩变形特性

在应变速率为0.005～5 s-1、变形温度为250～450℃条件下,在Gleeble-1500热模拟机上对AZ31镁合金的高温热压缩变形特性进行了研究.结果表明:材料流变应力行为和显微组织强烈受到变形温度的影响;变形温度低于350℃时,流变应力呈现幂指数关系;变形温度高于350℃时,流变应力呈现指数关系;变形过程中发生了动态再结晶且晶粒平均尺寸随变形参数的不同而改变,其自然对数与Zener-Hollomon(Z)参数的自然对数成线性关系;材料动态再结晶机制受变形机制的影响,随温度的不同而改变;低温下基面滑移和机械孪晶协调变形导致动态再结晶晶粒的产生;中温时Friedel-Escaig机理下位错的交滑移控制动态再结晶形核;高温时位错攀移控制整个动态再结晶过程.在本实验下,材料的最佳工艺条件是:变形温度350～400℃,应变速率为0.5～5 s-1.     

AZ31镁合金压缩过程中织构对微观变形机制的影响

以AZ31镁合金热轧板材为研究对象,利用电子背散射衍射(EBSD)技术,研究了与板材法向(ND)分别成0o,30°,60°和90°的试样在室温压缩过程中织构对滑移和孪晶启动的影响。结果表明,0°试样有很高的屈服强度但无明显的屈服平台。拉伸孪晶的临界剪切应力(CRSS)比基面滑移的大。随着角度的增加,试样产生的{10 ■2}拉伸孪晶越来越多。0°试样由于很难发生拉伸孪晶,变形主要由滑移来完成,小角度晶界增加明显。柱面滑移的作用使得60°试样的小角度晶界明显高于30°试样的小角度晶界。     

AZ31镁合金高应变速率轧制边裂及力学性能各向异性

在300~400 ℃对铸态AZ31镁合金进行平均应变速率为10~29 s^-1的高应变速率轧制,研究轧制后镁板边裂、组织及力学性能的各向异性。结果表明:随着平均应变速率的增加,轧制边裂得到改善,350 ℃和400 ℃下边裂长度变化相比300 ℃时更加平缓;晶粒尺寸在温升和应变速率综合作用下并不随平均应变速率的增加而减小,反而出现波动;在相对较低的应变速率下,由于组织中长条形晶粒的存在,导致板材的各向异性明显;随着平均应变速率的增加,长条形晶粒减少,再结晶完全,组织趋于均匀,轧板的各向异性得到改善;轧板拉伸断口中可观察到撕裂棱和韧窝,以韧性断裂方式为主。     

采用元胞自动机结合Laasraoui-Jonas位错密度模型模拟AZ31镁合金的动态再结晶行为

采用元胞自动机结合Laasraoui?Jonas 位错密度模型(LJ模型)模拟AZ31镁合金在动态再结晶过程中的位错密度和微观组织演化。LJ模型中的硬化参数、回复参数和应变速率灵敏系数决定模拟的准确性。在目前的研究中,基于 LJ 模型和 Kocks?Mecking 模型(KM 模型)求解硬化参数;采用动态再结晶中的稳态应力公式求解回复参数和应变速率灵敏系数。结果表明：模拟结果与实验结果一致。     

Influence of hot extrusion on microstructure and mechanical properties ofAZ31 magnesium alloy

Extrusion treatment is a common method to refine the grain size and improve the mechanical properties of metal material. The influence of hot extrusion on microstructure and mechanical properties of AZ31 magnesium alloy was investigated. The results ,show that the mechanical properties of AZ31 alloy are obviously improved by extrusion treatment. The ultimate tensile strength （UTS） of AZ31 alloy at room temperature is measured to be 222 MPa, and is enhanced to 265.8 MPa after extrusion at 420℃. The yield tensile strength （YTS） of AZ31 alloy at room temperature is measured to be 84 MPa, and is enhanced to 201 MPa after extrusion at 420℃. The effective improvements on mechanical properties result from the formation of the finer grains during extrusion and the finer particles precipitated by age treatment. The features of the microstructure evolution during hot extruded of AZ31 alloy are dislocation slipping on the matrix and occurrence of the dynamic recrystallization.     

AZ31镁合金的热挤压变形和力学性能分析

为了掌握高精度镁合金管材的生产工艺,通过对铸锭的均匀化处理,借助500 t挤压机、拉伸试验机、金相显微镜和透射电镜(TEM)对AZ31镁合金管材的等温挤压过程进行了研究,试制了AZ31镁合金挤压薄壁管材,获得了尺寸精度高、粗糙度小和壁厚差小的管材;分析了不同挤压条件下的AZ31镁合金管材的尺寸精度、组织、力学性能.研究结果表明:在挤压温度为623士20K挤出管材经523K×3h退火时其性能较好,抗拉强度、屈服强度和延伸率分别为270 MPa,175 MPa和23.1%.     

AZ31镁合金的各向异性及断裂行为

研究织构和异常长大晶粒对热轧AZ31镁合金力学各向异性和断裂行为的影响.在拉伸轴与板材的法向方向分别呈0°、15°、30°、45°、60°、75°和90°下进行单轴拉伸实验,观察不同角度下样品的拉伸各向异性.结果表明:由于{1012}孪晶的出现,在0°-30°时样品表现出较低的屈服强度;当角度大于45°时,样品的主要的变形机制为基面和柱面滑移;当角度低于60°时,宏观断口平行于大晶粒拉长的方向;在75°和90°时样品的宏观断口呈锯齿状.     

工业态AZ31镁合金的超塑性变形行为

研究了工业态AZ31镁合金在温度 6 2 3～ 72 3K和应变速率 1× 10 -5～ 1× 10 -3 s-1范围内的超塑性变形行为。结果表明 ,工业态AZ31镁合金表现出良好的超塑性 ,其最高断裂延伸率达到 314%,应变速率敏感指数达 0 .4。显微组织观察和断口分析表明 ,工业态AZ31镁合金超塑变形主要由晶界滑动机制所控制 ,同时 ,动态再结晶也是合金超塑变形的一种协同机制。     

Influence of strain rate on microstructure and formability of AZ31B magnesium alloy sheets

The effects of strain rate on microstructure and formability of AZ31B magnesium alloy sheets were investigated through uniaxial tensile tests and hemispherical punch tests with strain rates of 10^?4, 10^?3, 10^?2, 10^?1 s^?1 at 200 °C. The results show that the volume fraction of dynamic recrystallization grains increases and the original grains are gradually replaced by recrystallization grains with the strain rate decreasing. A larger elongation and a smaller r-value are obtained at a lower strain rate, moreover the erichsen values become larger with the strain rate reducing, so the formability improves. This problem arises in part from the enhanced softening and the coordination of recrystallization grains during deformation.     

镁合金超塑性变形的损伤演化效应

研究了AZ31B镁合金板材超塑性变形时的空洞损伤,对拉伸试样在超塑性变形各阶段轴剖面的空洞进行了观察,通过对空洞演化的分析建立了空洞体积分数与变形程度的定量关系,并推导出基于微损伤演化规律及统计细观损伤力学的损伤演化方程,通过试验得到适用于AZ31B镁合金板材超塑性变形损伤演化的特征参数C1、C2和损伤变量临界值DC.     

单轴拉伸与压缩加载下AZ31镁合金单晶的各向异性塑性行为(英文)

为研究HCP结构单晶在塑性变形中的变形孪晶和塑性各向异性,采用基于晶体塑性本构理论的有限单元法,建立包含滑移与孪生变形机制的晶体塑性本构关系,发展了以应力作为自变量的牛顿-拉普森迭代方法,通过已有文献的试验数据验证模型的有效性,并利用此模型模拟AZ31单晶体在4种(即沿〈2110〉,〈0110〉,〈0001〉和〈0111〉方向)拉伸与压缩变形路径下的塑性变形行为,并获得了相应加载路径下的应力-应变关系曲线。数值计算结果表明,在不同加载路径下该模型可用于预测滑移系或孪生系的活动情况,以及描述孪生变体的活动数量、主要孪生变体和孪生交叉类型。由于机械孪晶具有的极性性质及其在材料非弹性变形中的重要作用,单晶材料表现出显著的各向异性与非对称性。     

AZ31镁合金铸坯均匀化退火

研究了一种新的均匀化退火工艺对AZ31镁合金铸坯组织转变和成分均匀化的影响,保温温度为530、540和550 ℃以及保温时间为30、60和90 min.结果表明,AZ31镁合金在固相线温度以下应尽可能提高退火温度,同时缩短退火时间可使铸坯达到较好的均匀化效果,消除大部分枝晶偏析,γ-Mg_(17)Al_(12)相在α-Mg基体上呈细小的颗粒状分布; AZ31镁合金铸锭的优化退火工艺为540 ℃保温60 min.     

Hereditary transmission ofAZ91D magnesium alloy

The magnesium ingots from factory A, B and C were remelted. The microstructure and property of un-remelted and remelted magnesium ingots were investigated. The results indicate that the microstructure and property of the remelted magnesium alloy take on a hereditary transmission similar or resembling to those of feed materials. The characteristics of the short range order structure atomic group in alloy is the same as or resembles to that of feed materials during the melting process. The hereditary transmission of magnesium alloy can be explained by atomic conglobation theory.     

Compressive deformation behavior of AZ31 magnesium alloy under quasi-static and dynamic loading

Compressive properties of AZ31 alloy were investigated at temperatures from room temperature to 543 K and at strain rates from 10-3to 2×10 4s-1.The results show that the compressive behavior and deformation mechanism of AZ31 depend largely on the temperature and strain rate.The flow stress increases with the increase of strain rate at fixed temperature,while decreases with the increase of deformation temperature at fixed strain rate.At low temperature and quasi-static condition,the true stress-true strain curve of AZ31 alloy can be divided into three stages(strain hardening,softening and stabilization) after yielding.However,at high temperature and high strain rate,the AZ31 alloy shows ideal elastic-plastic properties.It is therefore suggested that the change in loading conditions(temperature and strain rate) plays an important role in deformation mechanisms of AZ31 alloy.