锆合金热变形过程中的织构演变研究

本文选取了一种热轧退火态的锆合金板材沿着其板材法向(0°样品)及横向(90°样品)在700 ℃温度下以1/s应变速率进行压缩试验。利用电子背散射衍射(EBSD)技术对变形后样品的微观组织及织构进行表征,并利用粘塑性自洽模型(VPSC)确定了在低应变条件下的各滑移系及孪晶的相对开启量。微观组织揭示了在两种样品中均有动态再结晶的发生。再结晶晶粒的织构变化与变形晶粒的织构变化相似,表明了再结晶过程中的优先形核及长大过程不会影响织构的形成及变化。在0°样品中,基面滑移、柱面滑移和锥面滑移在变形初期阶段同时开启,但是在90°样品中,只有少量的锥面滑移在变形初期阶段开启。在90°样品中存在的高强度的<10-10>//RD 织构组分是由大量开启的柱面滑移造成的。此外,700 ℃温度下大量基面滑移的开启对织构形成起重要作用。     

多相V-Ti-Ni氢分离合金异步轧制组织与性能

研究了铸态和热处理态多相V₆₀Ti₂₀Ni₂₀氢分离合金的异步轧制性能,异速比对合金显微组织、硬度和织构系数的影响。研究表明,异步轧制工艺提升合金轧制性能的效果高于热处理工艺提升的效果。热处理加异步轧制能够有效大幅提升合金的轧制成形性能。合金异步轧制性能随着异速比增加而增加,合金的硬度几乎不随轧制异速比的变化而变化。高的轧制压下量下,合金呈现出明显流变特征,V基固溶体(Vss)和NiTi 相变形量大,沿轧制方向变形伸长,成层状组织。随着合金轧制异速比增加,合金显微组织沿厚度方向逐渐出现低程度的不均匀变形,中心位置变形程度高于同步轧制。异步轧制沿厚度方向引入的剪切变形能在一定程度上弱化合金的轧制织构。     

微量Ce和Ca对AZ31组织演变及成形性能的影响

研究微量(0.2%,质量分数)Ce和Ca对AZ31合金组织演变和成形性能的影响,期望通过改善组织和织构开发低成本高成形性能的镁合金。结果表明:Ce和Ca可以使挤压态AZ31板材再结晶晶粒更加均匀细小;Ce和Ca可以弱化轧制退火态板材的基面织构,Ca会使AZ31板材的基面织构基极向横向发散,同时,Ce和Ca还能使AZ31板材的r值和各向异性降低;Ce和Ca可以大幅提高AZ31合金板材的室温成形性能,Mg-3Al-1Zn-0.2Ce-0.2Ca合金薄板的基面织构强度为3.2,r值为1.05,Δr值为0.04,其Erichsen值达到6.0 mm。织构的改善主要是由于合金元素引起的滑移系的改变,板材各向异性的降低与其织构的改善密切相关,室温成形性能的提高可以归因于织构的改善、较小的r值和较大的n值。     

AZ80镁合金热挤压织构的多晶体建模（英文）

为合理模拟AZ80镁合金的热挤压织构,在粘塑性自洽(VPSC)多晶体塑性框架中实现了动态再结晶织构的模拟。基于此模型,考察了挤压温度和挤压边界条件对AZ80镁合金挤压织构的影响,模拟所得结果与实验结果有较好的吻合。模拟结果表明:新的大角度界面(HABs)的形成使再结晶晶粒与母晶之间形成取向差,再结晶晶粒因此偏离母晶形成了{2110}纤维织构组分。此外,因为基面a滑移具有更低的滑移抗力并易于开动,当垂直于挤压轴方向上加载的应变不再轴对称时,晶粒的基面总倾向于转向加载应变更多的方向以便于基面a滑移承载更多的塑性变形。挤压温度的升高有利于锥面c+a滑移的开动并使再结晶体积分数增多,在一定程度上弱化了挤压形成的基面织构。     

特殊成形工艺下AZ31镁合金的织构及变形机制

通过组织观察以及宏观和微观织构测定、分析了异步轧制及等径角轧制的AZ31镁合金形变机制,确定了在这两种工艺下{0001}基面织构的改善效果.结果表明:异步轧制产牛的平行于轧面的剪切力促进了与普通轧制状态下相反的基面滑移,使基面织构连续地弱化为倾转的基面织构;而等径角轧制通过产生与轧向成122.5°的剪切力,使基面取向的晶粒产生拉伸孪晶,形成与基面织构共存的柱面织构.因此这两种特殊工艺都可能改善镁合金的塑性.还分析了形变量和退火对织构的影响.     

等通道挤压对AZ80镁合金的组织和织构的影响

研究了AZ80镁合金在300℃下经A路径等通道挤压后显微组织和织构的演变规律,揭示了该应变路径下织构特征形成的内在机制,并讨论了ECAP对第二相析出的影响。结果表明:材料经ECAP后最终获得3~4μm的等轴晶,并显著促进了粒状Mg17Al12相的连续析出,但增加挤压道次晶粒细化效果减弱,粒子粗化;挤压初始可获得基面法线向挤压方向偏转的倾斜织构与基面织构共存的织构特征,在剪切面倾斜度效应和通道间隙的影响下,随着挤压道次的增加,倾斜织构的偏转程度减小,最终获得单一的基面织构。     

AZ31镁合金挤压薄板织构及力学各向异性

研究AZ31镁合金挤压薄板的显微组织、织构及室温下板面内各不同方向的力学性能。织构分析表明,挤压薄板主要有{0002}<1-010>和{10-10}<11-20>2种织构组分。拉伸测试结果显示,沿挤压方向屈服强度最高,达到200.4MPa,这是由于这种取向基面滑移和{1-012}锥面孪生均不能开动,发生织构强化的结果;与挤压方向呈45°方向伸长率最高达19.0%,这是由于具有{10-10}<11-20>织构组分晶粒的基面滑移开动;与挤压方向呈90°方向屈服强度最低仅为挤压方向相应值的一半左右,这是由于具有{10-10}<11-20>织构组分晶粒发生了{10-12}锥面孪生。     

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。     

预压缩对热挤压AZ91-2Y镁合金动态析出相形成及蠕变各向异性的影响（英文）

研究经预压缩(PC)和未经预压缩(NPC)的热挤压AZ91-2Y镁合金在180°C不同应力下的蠕变各向异性行为。采用扫描电子显微镜(SEM)、电子背散射衍射(EBSD)、透射电子显微镜(TEM)和拉伸蠕变试验对合金的显微组织、织构和力学性能进行分析。结果表明,抗蠕变性能与球形Mg₁₇Al₁₂析出相的体积分数成正比。NPC试样中动态析出高体积分数层片状Mg₁₇Al₁₂,使其以基面滑移为主导蠕变机制,且NPC试样具有明显的各向异性。PC试样动态析出高体积分数的球形Mg₁₇Al₁₂,对基面滑移有抑制作用。锥面滑移和孪晶显著提高蠕变各向异性抗力。     

ZK60镁合金异步降温轧制显微组织与力学性能的演变（英文）

将异步降温轧制应用于制造沿轧制方向具有弱基面织构的细晶ZK60镁合金板。结果表明,多道次降温轧制可以显著改善显微结构的均匀性,细化晶粒尺寸。同时,在轧制过程中逐渐形成沿横向的纤维织构。重要的是,沿轧向的剪切变形使基面的c轴向轧向旋转,削弱沿此方向的基面织构。受这种显微结构变化的影响,由于连续的晶粒细化和柱面滑移的增加,沿横向的屈服强度持续增加,而由于应变硬化能力的下降,均匀伸长率下降。相反,沿轧向的基面织构的持续减弱大大抵消晶粒细化所带来的强化效果,从而导致屈服强度的轻微下降。     

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.     

挤压镁合金AZ31的压缩过程中的组织及织构演化

对常规挤压态镁合金AZ31压缩过程的组织及织构演化进行了扫描电镜-电子背散射衍射(SEM-EBSD)原位观察。结果表明材料的初始组织为等轴晶,晶粒的平均尺寸为76微米,晶粒内部未发现形变孪晶。材料的初始织构类型为典型的{11-20}丝织构,即大多数晶粒的<11-20>晶向平行于棒材的挤压方向(ED)。在压缩过程中,多数晶粒内部开始出现拉伸孪晶,随着压缩应变的增加,孪晶片层不断增厚,导致晶内的孪晶合并成大的孪晶并占据晶粒内部的大部分区域进而使孪晶的体积分数不断增加。随着压缩压缩应变的增加初始丝织构不断减弱并有新的基面织构形成。实验表明压缩过程中的{10-12}<10-11>孪生而非滑移是引起压缩过程中织构演化的主要原因。     

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.     

锆合金挤压管坯的组织及织构研究

采用XRD和EBSD技术,对不同挤压温度(650和630℃)的2种锆合金管坯的显微组织和宏观织构进行研究。结果表明,管坯内发生了动态回复和再结晶,其组织由沿挤压方向拉长的大晶粒与近似等轴的再结晶晶粒组成,管坯内再结晶晶粒的平均尺寸相近,分别为0.44和0.41μm,温度对显微组织无显著影响;挤压温度为650℃的管坯的织构主成分为<1010>纤维织构及{0001}<1010>,630℃挤压管坯的织构主成分为<1120>纤维织构及{0001}<1120>,并且后者基轴在管材横向的分布强度略高于径向分布。     

Effect of Partially Substituting Ca with Mischmetal on the Microstructure and Mechanical Properties of Extruded Mg-Al-Ca-Mn-Based Alloys

Mg-2Al-1.2Ca-0.2Mn(at%)-based alloys with Ce-rich mischmetal(MM) substitution of 0–0.6 at% for Ca were hot extruded at 400 °C. The effect of MM substitution on the microstructure and mechanical properties of the extruded alloys was investigated. The as-cast Mg-2Al-1.2Ca-0.2Mn alloy is mainly composed of a-Mg, Mg_2Ca and(Mg,Al)_2Ca phases and Al_8Mn_5 precipitates, whereas the substitution of MM brings about the formation of Al_(11)MM_3, Al_2MM phases and Al_(10)MM_2Mn_7 particles with the absence of (Mg,Al)_2Ca phase. The volume fraction of MM-containing phases increases with increasing MM contents. All of the extruded alloys exhibit bimodal microstructure comprising fine dynamically recrystallized grains with almost random orientation and coarse deformed grains with strong basal texture. Dense nanosized planar Al_2Ca and spherical Al–Mn phases precipitate inside the deformed grains. High tensile yield strengths of~ 350 MPa and moderate elongations to failure of 12% are obtained in all extruded alloys; the MM substitution induces negligible difference in the tensile properties at ambient temperature, while the highest MM substitution improves the strength at 180 °C due to the better thermal stability of the fragmented MM-containing phases.     

Effect of Forging on Microstructure,Texture, and Uniaxial Properties of Cast AZ31B Alloy

The effect of open-die hot forging on cast AZ31B magnesium alloy was investigated in terms of the evolution of microstructure, texture, and mechanical properties. A refined microstructure with strong basal texture was developed in forged material. A significant increase in tensile yield and ultimate strengths by 143 and 23%, respectively, was determined as well. When tested in compression at room temperature, the forged alloy displayed significant in-plane asymmetry and unchanged yield strength compared to the cast alloy owing to the activation of \(\left\{ {10\bar{1}2} \right\}\left\langle {10\bar{1}1} \right\rangle\) extension twins in both the cast and forged conditions. However, the ultimate compressive strength for the forged material increased by 22 percent compared to the as-cast material. Microstructure and texture analysis of the fracture samples confirmed that the deformation of the forged samples was dominated by slip during tension and twin in compression. In comparison, both slip and twin were observed in the cast samples for similar testing conditions. The increase in strength of forging was attributed to the refinement of grains and the formation of strong basal texture, which activated the non-basal slip on the prismatic and pyramidal slip systems instead of extension twin.     

Influence of Ca Content on Microstructure and Mechanical Properties of Extruded Mg-Al-Ca-Mn Alloys

Herein, the effects of Ca content on microstructure, texture and mechanical properties of extruded Mg-3Al-0.4Mn-xCa (x = 0.4, 0.8 and 1.2 wt%) rods are systematically investigated. The results reveal that the alloy, with Ca content of 0.8 wt%, exhibits the highest strength and ductility, possessing an ultimate tensile strength of 267.57 MPa and elongation (EL) of 16%. This is mainly due to the gradual transformation of typical fiber texture into a texture with a [10-11] component parallel to the extrusion direction (ED), which increases the Schmid factor of pyramidal slip and enhances the activation rate of pyramidal ⟨c + a⟩ slip. Simultaneously, the as-formed spherical phases and segregation of Ca at grain boundaries render a significant influence on the strength and ductility of the alloy.     

复合添加Y和Nd对Mg-Li合金显微组织及室温压缩织构的影响

采用OM,SEM,XRD,EBSD及电子万能试验机,对比研究了Mg-5Li-3Al-2Zn和Mg-5Li-3Al-2Zn-1.2Y-0.8Nd铸态合金的显微组织、力学性能以及室温单向压缩后的织构演变.研究发现,复合添加Y和Nd 2种稀土元素后,合金中絮丝状AlLi相明显减少,晶粒得到显著细化,平均尺寸在30μm左右.2种合金的塑性表现良好,加入少量稀土的合金室温压缩的变形量可达到27%.复合添加的稀士元素大幅度降低了Mg品格的c/a值,显著弱化了合金的基面织构,激活了锥面滑移系的同时,也使得室温下少见的柱面滑移破激活.     

Microstructure and mechanical properties of AM31 magnesium alloys processed by differential speed rolling

Ingot casted AM31 alloys were rolled at a warm temperature of 350 °C and subsequently rolled at 300 °C using equal speed rolling (ESR) and differential speed rolling (DSR) with speed ratios of top roll to bottom roll, 1.2 and 1.5, respectively. Microstructures, textures and mechanical properties of the as-rolled AM31 sheets were examined. Ductility was improved by DSR due to inclination of basal poles and weakened texture. The sheets produced by DSR with a speed ratio of 1.2 showed highest strength and ductility at room temperature, which can be attributed to homogeneous fine grain distribution and tilted basal texture.     

Texture of AZ31B magnesium alloy sheets produced by differential speed rolling technologies

The effects of differential speed rolling (DSR) on the texture of AZ31B magnesium alloy sheets were investigated,which were achieved by tailoring deformation temperature,reduction,and speed ratio.The results show that the intensity of basal texture weakens with DSR.With the increase of the rolling temperature,the intensity of basal texture decreased first and then increased,which had a relation with the change of the orientation of the new grains of dynamic recrystallization during rolling.The effect of the reduction on the basal texture was made with the changing degree of sharp point of texture.With increasing the deformation at the same rolling temperature,the intensity of basal texture decreased,and the extending of contour lines decreased in the transverse direction,which was close to the circular distribution.Differential speed ratio has a greater impact on the intensity of the basal texture and has a less effect on the basal deflection.