Microstructure and Texture Evolution During the Direct Extrusion and Bending–Shear Deformation of AZ31 Magnesium Alloy

AZ31 alloys were extruded by direct extrusion and bending–shear deformation(DEBS). The microstructure characteristic and texture evolution of DEBSed AZ31 sheets were investigated by electron backscattered diffraction(EBSD). It is found that DEBS technique could effectively refine grains and weaken texture. Besides, we also investigate how twinning affects dynamic recrystallization during hot extrusion. {10–12} extension twins can offer nucleation sites and enough energy to trigger dynamic recrystallization. Moreover, the character of direct extrusion and bending–shear die can lead to the activation of non-basal slip system and further dramatically weaken the basal texture of the microstructure with many preactivated basal slip systems.     

Plastic flow anisotropy of pure zirconium after severe plastic deformation at room temperature

The present work investigates the plastic flow anisotropy of zirconium following one pass of equal-channel angular extrusion (ECAE) at room temperature in a 90° die. Samples were oriented with their strong basal pole texture either aligned with or perpendicular to the extrusion direction prior to processing, which leads to two significantly different starting textures. After ECAE, the samples were compressed to 30% along one of three sample directions. A visco-plastic self-consistent polycrystal model was used to determine the mechanisms responsible for the observed anisotropy. Using the same single-crystal material parameters, the model reasonably predicts texture evolution and the post-compression stress–strain response. We found that basal slip is crucial in reproducing the experimental results, and twinning makes an important contribution. These findings are noteworthy because basal slip is not active in zirconium at room temperature, and grain size reductions associated with ECAE are expected to suppress deformation twinning.     

纯钛板材冷拉成形过程中的微观组织与织构演变(英文)

研究纯钛板材冷拉成形过程中微观组织及织构演化规律。半球形壳体件在深拉延过程中由于各部位变形模式及应变形式的不同会形成胀形区、拉深区及法兰区等3个区域。结果表明,在拉深件的3个区域中塑性应变均由位错滑移与变形孪晶共同作用。纯钛板材及其拉深件中的织构包含轧制织构与再结晶织构。由于变形孪晶与位错滑移对织构的影响规律不同,初始板材织构的强度及类型在深拉过程中不断变化。变形孪晶对初始织构具有弱化作用,特别是对于再结晶织构,这种弱化效应更为明显。由于拉深区产生的孪晶较多,再结晶织构消失。此外,大拉伸变形时位错滑移为主导机制,织构强化效应明显。     

镁合金塑性变形力学行为与微观组织研究进展

介绍了镁合金在单轴压缩、单轴拉伸、轧制和挤压条件下塑性变形的力学行为及微观组织结构演变规律。简述了镁合金中二次拉伸孪生现象以及各种变形条件下孪生与孪生变体类型的选择规律。基于对镁合金位错滑移、机械孪生及动态回复与再结晶行为的认识,对镁合金力学行为的各向异性、轧制与挤压成型能力的影响规律进行了探讨,强调了初始织构对变形机制、动态再结晶及成型能力的重要影响。最后讨论了析出强化镁合金塑性变形与强韧化机理。     

Dependence of Microstructure Evolution and Mechanical Properties on Loading Direction for AZ31 Magnesium Alloy Sheet with Non-basal Texture During In-Plane Uniaxial Tension

In-plane uniaxial tension of AZ31 magnesium alloy sheet with non-basal texture has been conducted in order to demonstrate the effects of loading direction on the microstructure evolution and mechanical properties at ambient temperature. Loading axes are chosen to be along five directions distributed between rolling direction (RD) and transverse direction (TD), allowing various activities in involved slip and twinning modes to take place. As for twinning modes, electron backscattered diffraction observations confirm that the contribution of ${{\{ 10\overline{1}1\} }}$ compression twinning is minimal to the plastic deformation of all deformed samples. By comparison, ${{\{ 10\overline{1}2\} }}$ extension twinning (ET) not only serves as an important carrier on sustaining and accommodating plastic strain but also contributes to the emergence of TD-component texture with the progression of plastic strain. In terms of slip modes, analysis on Schmid factor demonstrates that the increasing tilted angle between loading direction and RD of sheet is unfavorable to the activation of basal <a> slip, whereas it contributes to the activation of prismatic <a> slip. These observations consequently explain the increasing tendency of 0.2% proof yield stress. Moreover, the activations of basal <a> slip and ${{\{ 10\overline{1}2\} }}$ ET collectively contribute to the concentration of two tilted basal poles toward normal direction. With increasing angle between loading direction and RD, the activations of basal <a> slip and ${{\{ 10\overline{1}2\} }}$ ET are gradually weakened. This leads to a weakening tendency about concentration of two tilted basal poles, a generally increasing tendency about Lankford value (r-value) and a generally decreasing tendency about strain-hardening exponent (n-value).     

挤压态AZ31镁合金的拉压不对称性及微观组织

在考虑滑移和孪生两大塑性变形机制的基础上,通过修正的粘塑性自洽（VPSC）模型,模拟挤压态AZ31镁合金轴向拉-压过程中的力学行为及微观组织。结合EBSD实验与模拟,分析了不同变形机制对初始挤压态丝织构镁合金产生拉压不对称的机理以及塑性变形过程中的微观组织。结果表明,轴向拉伸变形初期以基面滑移系为主,由于基面滑移的施密特因子较低,导致屈服应力较高;随着应变的增加,棱柱面滑移成为主导变形机制,应变硬化率降低,应力-应变曲线较平稳;轴向压缩变形初期,临界剪切应力较低的拉伸孪晶大量开启导致屈服应力较低;随着拉伸孪晶相对活性的快速降低,应变硬化率迅速提高;轴向压缩后期,随着应力的持续升高,压缩孪晶开始启动,塑性变形积累的应力得到释放,导致应变硬化率降低。另外,从典型晶粒的颜色和孪晶迹线方面解释了沿ED方向压缩时孪晶体积分数较小的原因。     

织构对Zr-4合金低周寿命的影响

采用XRD测定了Zr-4合金板材的织构，用拉扭试验机分别测试了Zr-4合金板材在室温时轧向（R试样，拉伸轴平行于轧向）和横向（T试样，拉伸轴平行于横向）的低周疲劳性能，用TEM研究了Zr-4合金的疲劳亚结构。结果表明：Zr-4合金板材存在明显的织构：轧向的低周疲劳性能高于横向；在循环变形过程中，只有部分晶粒发生了塑性变形，发生塑性变形的晶粒内存在着许多位错和滑移线，T试样中的位错和滑移线比R试样更稠密。板材织构造成了R试样和T试样的低周疲劳寿命。     

Microstructural Evolution and Biodegradation Response of Mg-2Zn-0.SNd Alloy During Tensile and Compressive Deformation

The effect of deformation behavior on the in vitro corrosion rate of Mg-2Zn-0.5Nd alloy was investigated experimentally after uniaxial tensile and compressive stress.The microstructure and texture were characterized using electron backscattered diffraction and X-ray diffraction,while potentiodynamic polarization and immersion tests were used to investigate the cor-rosion response after deformation.The result reveals that applied compressive stress has more dominant effect on the corro-sion rate of Mg-2Zn-0.5Nd alloy as compared to tensile stress.Both tensile and compressive strains introduce dislocation slip and deformation twins in the alloy,thereby accelerating the corrosion rate due to the increased stress corrosion related to dislocation slips and deformation twins.The { 10(1)2} tension twinning and prismatic slip were the major contributors to tensile deformation while basal slip,and { 10(1)2} tension twin were obtainable during compressive deformation.The twinning activity after deformation increases with the plastic strain and this correlates with the degradation rate.     

T5态7N01铝合金挤压型材的组织及拉伸性能各向异性

对T5热处理状态下的7N01铝合金挤压型材进行微观组织观察和拉伸强度测试。试验结果表明,7N01型材显微组织存在一定程度上的不均匀以及各向异性,沿挤压方向上的晶粒被拉长形成形变织构。这种形变织构能够更有效地抵抗挤压方向上的塑性变形,因此沿挤压方向的强度比垂直于挤压方向高,伸长率下降约2%。7N01铝合金挤压型材在室温抗拉强度约为368 MPa,屈服强度约为318 MPa,综合性能表现良好。     

In Situ Electron Backscatter Diff raction Analysis for Microstructure Evolution and Deformation Models of Mg–Ce Alloy During Uniaxial Loading

Previous studies showed that signifi cant increases in elongation in Mg–Ce alloys due to the Ce addition and the solute drag eff ect by Ce addition were ascribed to the non-basal dislocation slip activating and the texture altering. The microstructure evolution and deformation models of extruded Mg-0.5 wt%Ce alloy rods under uniaxial tension have been studied using in situ electron backscatter diff raction. The basal and non-basal slips were characterized by using slip line trace analysis. The results provide evidence for that pyramidal slip activated during deformation, besides basal slip and extension twinning, which contributes to the texture weakening and ductility increasing in Mg-0.5 wt%Ce alloy.     

基于VPSC仿真的ZK60镁合金拉伸变形行为

通过实验和粘塑性自洽（VPSC）模型,研究了在室温下挤压态ZK60镁合金沿不同方向拉伸时的变形机制开动情况,及其与流动曲线、织构演变和显微组织的对应关系。通过调节VPSC模型的参数,建立了滑移和孪生耦合的晶体塑性力学模型。比较了不同方向拉伸过程中织构演变的差异,分析了变形机制对屈服不对称性的影响。实验和模拟结果表明：当沿垂直于挤压方向（PED）拉伸时,由于｛102｝孪晶开动,大部分晶粒发生大角度旋转（约90°）。柱面<a>滑移是导致ZK60合金沿不同方向拉伸时出现明显屈服不对称的主要变形机理。当ZK60合金沿挤压方向（ED）拉伸时,由于晶粒的择优取向分布,｛101｝孪晶难以开动,导致ZK60挤压态镁合金拉伸屈服强度较高。ZK60镁合金沿着与ED成45°的方向拉伸时,屈服应力高于沿PED拉伸,但随着拉应力逐渐增大,由于沿PED拉伸时柱面<a>滑移逐渐开动,沿PED应变后期的应力曲线逐渐高于沿与ED成45°方向应变的应力曲线。     

Deformation structure during creep deformation in soft orientation PST crystals

Deformation microstructure of soft polysynthetically twinned (PST) crystals Ti–48A1 was investigated. The soft orientation with the lamellar plates oriented 35° to compression axis was deformed at 1150 K under applied stresses of 100–251 MPa. Macroscopically anisotropic deformation was observed after creep deformation. Deformation took place in the maximum shear stress direction in the soft orientation. Dislocation structures in γ domains of six different variants were examined by transmission electron microscopy. Operative slip and twinning systems were also analysed. Macroscopic plastic strain and strain compatibility at domain and lamellar boundaries were discussed in terms of the slip systems in each domain. Refinement of lamellar occurred by mechanical twinning during creep deformation.     

AZ31镁合金挤压板材的中温变形机理及软化机制(英文)

研究AZ31镁合金挤压板材在473～523K的温度范围内。应变速率0.001～1.0s-1压缩时的流变应力行为,计算板材沿挤压方向压缩时的激活能,并结合光学显微镜和透射电子显微镜探讨合金软化机制和变形机理之间的联系。结果表明,在中温下沿挤压方向压缩时,AZ31挤压态镁合金的变形激活能为174.18kJ/mol。这说明,由热激活位错交滑移所控制的动态再结晶是合金中温变形的主要软化机制。位错滑移是中温变形的主要变形机理,而孪生的作用则不大。其主要的动态再结晶机制为持续动态再结晶,并伴随少量的孪生动态再结晶。     

高应变速率下AZ31镁合金的各向异性及拉压不对称性

采用分离式霍普金森拉杆及压杆装置,研究挤压态AZ31镁合金高速变形下的各向异性及拉压不对称性,并从微观变形机制的角度探讨具有强烈初始基面织构的挤压态镁合金各向异性及拉压不对称性产生的原因。结果表明:在高速变形条件下,依据加载方向及应力状态挤压态AZ31镁合金的拉伸行为表现出很强的各向异性,但压缩行为的各向异性不明显;在挤压方向表现出很强的拉压不对称性,而在垂直于挤压方向的拉压不对称性很低。挤压态AZ31镁合金宏观上的各向异性及拉压不对称性是由于不同的微观变形机制所引起的。沿挤压方向拉伸的主要变形机制为柱面滑移,沿垂直于挤压方向拉伸及压缩的主要变形机制为锥面滑移;沿挤压方向压缩时初始变形机制为拉伸孪晶,当变形量为0.08(8%)左右时由于孪晶消耗殆尽,变形变而以滑移的方式进行。     

变形镁合金中的织构及其优化设计

针对变形镁合金存在的典型织构以及织构优化设计方面的研究工作和进展进行综合评述。镁合金由于基面滑移和{1 012}孪生是最容易开动的变形模式,在变形镁合金中容易形成挤压丝织构及轧制板织构。通过引入剪切变形,改变成型过程中外加应力的取向,能够有效地改变变形镁合金的织构,同时通过添加微量稀土元素Nd、Ce和Y等,能够明显弱化或随机化变形镁合金织构。织构随机化后的镁稀土合金具有较好的强韧性,合金的变形各向异性得以改善。添加稀土元素后会改变稀土元素与Mg原子间的键能,改变稀土元素周围Mg-Mg原子之间的结合能等,增加非基面滑移的可能性,减弱基面滑移及{1 012}孪生所占的比率,有效地弱化镁合金的织构。     

AZ31B镁合金轧制板材室温动态拉伸的SEM观察

利用动态拉伸台和扫描电镜(SEM)对AZ31B镁合金轧制板材进行了动态拉伸的微观形貌观察。试验证明,材料宏观织构和显微组织都会对镁合金轧制板材的室温拉伸性能产生影响;在轧制镁合金拉伸变形时滑移和孪生同时存在;裂纹的产生和扩展具有明显的方向性。轧制组织中大量的变形孪晶与应力方向的位向关系,是轧向和横向上裂纹产生及扩展机制产生较大差异的主要原因。     

基于滑移/孪生耦合模型的镁合金多晶体塑性成形分析

镁合金的各向异性是由滑移和孪生共同作用产生,而孪生是协调镁合金塑性变形的重要机制。尤其在低温变形条件下,滑移和孪生相互协调并影响其成形性能。为准确描述镁合金成形过程的变形机制,文章建立了一种基于滑移和孪生相互耦合的多晶体塑性模型,并引入到有限元分析过程中。其中金属塑性流动,由每个晶粒内滑移面上沿滑移方向产生的剪切变形及孪生面上的孪生变形共同组成,进而采用率无关晶体塑性模型模拟了AZ31镁合金压缩过程,并给出了孪晶体积分数随时间的变化曲线。研究表明,孪晶体积分数随变形应力产生相应变化,并且基面滑移和孪生是影响镁合金室温成形性能及加工硬化的主要因素。     

Study on Deformation Structure and Texture of Pure Zirconium with Large Grain Size Rolled at Liquid Nitrogen Temperature

主要研究大晶粒退火态纯锆在液氮温度下均匀轧制时的形变组织特征及孪生机制。利用光学显微镜、扫描电镜、电子背散射衍衬（EBSD）、X射线衍射等对不同变形量样品的变形组织和织构进行了研究,重点结合软件对EBSD结果进行组织重构和机理分析。结果表明,液氮温度轧制时大晶粒纯锆中产生的孪晶类型为C1{112}<11>、T1{102}<10>和T2{111}<11>孪晶,其中C1{112}<11>孪晶最容易产生且为主要孪生类型。变形开始时,3种孪晶的数量迅速增多,而小角度晶界含量较少;变形量增大到30%时,小角度晶界含量占优势。变形初始阶段孪生优先于滑移进行, 且孪生变形是最主要的变形方式,当变形量为30%时,孪晶协调的位错滑移成为主要的变形方式。变形过程中织构类型未发生变化,保持基面双峰织构（偏离ND方向±30°左右）,但强度随着变形量的增大呈减小趋势