AZ31镁合金再结晶退火的准原位EBSD研究

对AZ31镁合金热挤压板进行室温轧制(形变量为8%)后,利用背散射衍射技术原位(in-situ EBSD)观测了轧制试样中不同类型的孪晶组织在再结晶退火过程中的取向演变。结果表明:退火过程中拉伸孪晶区域形成尺寸相对粗大的再结晶新晶粒,再结晶晶粒取向与拉伸孪晶的取向较为接近;压缩孪晶/双孪晶区域形成了细小的再结晶晶粒,再结晶晶粒偏离基面取向。孪晶再结晶显著影响镁合金在退火过程中的织构演变,轧制样品中,拉伸孪晶再结晶使得基面织构强度增强,压缩孪晶再结晶则可以在一定程度上弱化镁合金的基面织构。     

不同轧制工艺参数条件下AZ31镁合金孪晶和织构的演变规律及其对力学性能的影响（英文）

为了考察轧制工艺参数对板材显微组织和力学性能的影响,通过不同温度和轧制变形量的热轧工艺得到具有不同晶粒尺寸、基面织构强度和孪晶类型的AZ31镁合金轧制板材。拉伸孪晶、压缩孪晶和双孪晶的体积分数与AZ31镁合金轧制板材的晶粒尺寸有关。当轧制温度为523 K、轧制变形量为10%时轧制得到的板材,三种类型孪晶的体积分数最高,此时晶粒尺寸最大。在轧制温度分别为523和473 K时,板材发生完全动态再结晶的临界变形量分别为30%和40%。拉伸实验结果表明:随着轧制变形量的增加,在第一阶段,轧制后板材屈服强度的提高主要依赖于晶粒细化强化和织构强化;当晶粒尺寸随变形量的增加不再发生明显的细化时,板材的屈服强度主要受织构弱化的影响。     

非对称轧制AZ31镁合金板材组织与性能

采用商用连铸连轧AZ31镁合金板材,通过小辊径非对称轧制工艺,研究在150,200,250℃温度条件下多道次非对称轧制对镁合金板材组织、织构和力学性能的影响。结果表明,不同轧制温度下,镁合金板材的晶粒细化机理不同,150℃时以孪晶细化为主,部分晶粒发生动态再结晶,200和250℃时板材晶粒细化机理为动态再结晶。对比分析了对称轧制和非对称轧制板材织构演化规律,随着轧制温度的升高,非对称轧制板材基面织构依次增强,但明显低于对称轧制板材。     

轧制温度对AZ31镁合金轧制板材中的{1011}-{1012}双孪生行为的影响

在150-350℃温区内不同温度下轧制AZ31镁合金板,观察了不同温度下轧制变形量为9%的AZ31镁合金板材的显微组织,研究分析了轧制温度对轧制板材中{1011}-{1012}双孪晶的含量、类型以及高温轧制过程中双孪晶中的动态再结晶行为的影响,讨论了板材中的孪晶对其力学性能的影响.研究结果表明:在150-300℃温区内轧制时,板材组织中均有含量不等的{1011}-{1012}双孪晶,随着轧制温度的升高,孪晶含量下降.250℃以上轧制的板材中单片一次孪晶中出现的双孪晶类型较为单一,仅出现共面型双孪晶.在250℃以上轧制板材中的双孪晶晶界处中可以观察到明显的动态再结晶现象,这些动态再结晶晶粒对孪晶界和孪晶起到消除和吞噬的作用.350℃下轧制的AZ31镁合金板材中未观察到{1011}-{1012}双孪晶.随着轧制温度的升高,镁合金轧制板材的强度减弱而塑性增强.     

汽车用AZ31镁合金板材轧制工艺研究

采用光学显微镜(OM)、硬度测试等手段研究了轧制温度和压下率对AZ31镁合金铸轧板材显微组织和硬度的影响。结果表明:轧制温度350℃和总压下率72%轧制的AZ31镁合金试样组织中有大量孪晶出现,细小的再结晶晶粒分布在孪晶内部和α相晶界处,将大尺寸晶粒分割成较小晶粒,未发生再结晶的晶粒明显发生扭曲变形,组织得到明显细化。在350～410℃,随着轧制温度的升高,AZ31镁合金试样平均晶粒尺寸逐渐增大,试样硬度逐渐降低。轧制温度350、380、410℃,总压下率72%时,试样的硬度分别为86.6、84.7、79.5HV。     

AZ31B镁合金的铸轧组织及其相关变形机制

利用金相显微镜、透射电子显微镜对AZ31B镁合金铸轧板坯的微观组织进行研究.结果表明:铸轧AZ31B镁合金板坯主要由α-Mg基体、枝晶间Mg17Al12共晶体和弥散分布的细小析出相组成,铸轧对晶粒的细化效果不明显;板坯在铸轧过程中经历一定的塑性变形,且变形多分布于板材表层;塑性变形在合金中产生大量的位错及位错胞的同时,也产生一定数量的孪晶;经孪生改变晶体取向后的晶粒会在适合的条件下发生滑移变形,孪生和滑移的协同作用使孪晶和位错共存、孪晶中位错的产生和孪晶的变形;铸轧时的塑性变形和高温还导致回复和再结晶的发生.     

强织构AZ31镁合金板材深低温轧制过程中微观组织演变及力学性能控制研究

取初始织构为c轴与板面法向垂直的强织构AZ31镁合金板材为初始样品,经液氮温度深低温轧制多道次至不同变形量,研究所得轧制板材的显微组织与织构演变,及其对轧制力学性能的影响。利用SEM、EBSD和XRD表征分析了轧制板材的显微组织和织构,应用准静态单轴拉伸实验分别测试了深低温轧制板材沿轧向(RD)和横向(TD)的室温力学性能。研究表明,{1012}拉伸孪晶是深低温轧制强织构AZ31镁合金板材中的主导孪晶类型,其对轧制板材的微观组织和织构影响较为显著。轧制变形后,大量的拉伸孪晶晶界不但对晶粒起到了分割碎化作用,并且由于孪晶对取向的剧烈改变,使得板材在轧制变形后c轴平行于ND的织构组分加强。深冷轧制板材的强度有所提高,但是延伸率却急剧下降,沿着RD方向的强度要高于TD方向的强度。     

铸轧AZ31镁合金板温轧过程微观组织及裂纹研究

研究了铸轧AZ31镁合金在125、175、225℃及单道次压下量10%和15%温轧工艺条件下板带金相组织、XRD和裂纹变化规律。结果表明:低温轧制过程塑性变形主要是孪晶,变形带和剪切带,随变形量增加,粗大晶粒减小,条状孪晶增加;随温度升高,组织发生了部分再结晶,单道次变形量增加,晶格畸变加剧,再结晶晶粒增多;温轧后形成了典型基面织构(0002),且强度峰值随温度升高和压下量增加明显增强;尽管动态再结晶对裂纹愈合有明显积极作用,但过大压下量和过快温降导致变形不均匀性增加和裂纹无法完全消除。压下量10%,轧制温度200~250℃有利于铸轧AZ31镁合金后续温轧过程塑性改善和裂纹愈合。     

变形方式、动态再结晶和孪晶对AZ31镁合金轧制织构演变的影响（英文）

为了获得AZ31镁合金轧制织构(0002)基面密度和轧制条件的定量关系,在压下量为20%~40%、轧制温度为300~500°C的条件下对AZ31镁合金进行热轧试验。采用板材中嵌入镁合金圆柱的方法计算板材厚度方向的剪切应变和等效应变量。利用光学金相显微镜、X射线衍射和EBSD技术检测轧制板材的显微组织、表面层和中心层(0002)基面织构密度。定量分析应变、动态再结晶和孪晶对AZ31镁合金轧制板材织构的影响。结果表明:在相同应变下,轧制开始温度为400°C时,(0002)基面织构极密度最高,并得到了(0002)基面织构极密度随温度和应变的变化规律。     

热轧及退火处理对AZ31镁合金板材组织的影响

采用单向轧制的方法制备了AZ31镁合金板材,分析了不同轧制温度、道次变形量等工艺参数对组织性能的影响规律.研究结果表明,在多道次轧制时,当轧制温度为400℃,单道次变形量为25%时,所得到的AZ31镁合金板材经过热处理后的晶粒细小且均匀,板材平均晶粒尺寸达到6 μm;当轧制温度为400℃,单道次变形量为35%时,得到的板材平均晶粒尺寸为10μm.在轧后热处理时,当热处理温度低于150℃,且保温时间为30 min的情况下,轧制板材再结晶不完全;当热处理温度在250～300℃之间时得到的板材平均晶粒尺寸为5μm;当热处理温度超过350℃时轧制板材再结晶组织粗大而且孪晶组织消失.当热处理温度为320℃,且保温时间为15 min时,开始发生再结晶,再继续增加保温时间到120 min时对组织没有明显影响.     

Improving single pass reduction during cold rolling by controlling initial texture of AZ31 magnesium alloy sheet

The AZ31 magnesium alloy sheets obtained by multi-pass hot rolling were applied to cold rolling and the maximum single pass cold rolling reduction prior to failure of AZ31 magnesium alloy was enhanced to 41%. Larger single pass rolling reduction led to weaker texture during the multi-pass hot rolling procedure. The sheet obtained showed weak basal texture, while the value was only 1/3–1/2 that of general as-rolled AZ31 Mg alloy sheets. It was beneficial for the enhancement of further cold rolling formability despite of the coarser grain size. The deformation mechanism for the formation of texture in AZ31 magnesium alloy sheet was also analyzed in detail.     

Effect of plane strain on microstructures and texture, through the reduction ratio of AZ31 Mg alloy

Structural evolution of warm-rolled AZ31 alloy sheets was investigated with respect to various reduction ratios. In order to examine the effect of rolling pass on deformation of the sheet, one-pass rolling was applied to the AZ31 alloys for various 6/1/2011reduction ratios. When the applied reduction ratio was ∼85% of the initial thickness, significant grain refinement and texture development were achieved with dynamic recrystallization. Moreover, with the increase of the rolling reduction ratio from 30% to 85%, the warm rolled sheets exhibit plane strain mode displaying uniform 〈0 0 0 1〉//ND basal textures throughout the whole sheet thickness. The two-dimensional finite element method simulation showed that the current lubrication rolling results in a uniform plane strain deformation through the whole warm rolled sheet.     

Influence of rolling route on microstructure and mechanical properties of AZ31 magnesium alloy during asymmetric reduction rolling

Four different routes of asymmetric reduction rolling were conducted on AZ31 magnesium alloy to investigate their effect on the microstructure evolution and mechanical properties. Route A is the forward rolling; while during routes B and C the sheets are rotated 180° in rolling direction and normal direction, respectively; route D is the unidirectional rolling. The strain states of rolled sheets were analyzed by the finite element method, while the microstructure and texture were observed using optical microscopy, X-ray diffraction and electron back-scattered diffraction techniques, and the mechanical properties were measured by tensile test. The results show that route D produced the largest effective strain. Compared with other samples, sample D exhibited a homogeneous microstructure with fine grains as well as a weak and tilted texture, in corresponding, it performed excellent tensile properties, which suggested that route D was an effective way to enhance the strength and plasticity of AZ31 sheet.     

同步和异步轧制AZ31镁合金板材的织构及力学性能

采用同步轧制(NR)和异步轧制(AR)工艺对AZ31镁合金挤压板材进行了轧制,研究了轧制过程中组织和织构的演化,以及总压下量和异步比对轧材组织、织构和力学性能的影响。结果表明,在压下量为3%～15%的范围内,同步轧制与异步轧制板材在晶粒尺寸以及均匀性上有相似的变化趋势。轧制过程中,在变形初期,随压下量的增加,孪晶数量不断增加,孪晶使同步轧制与异步轧制板材中晶粒取向都发生偏转,即C轴趋向于垂直于法向(ND),从而使初始挤压板材的丝织构强度减弱;而当压下量达到24%时,孪晶大量减少或消失。在压下量为3%～24%的范围内,同步轧制对板材力学性能的影响并不明显,峰值应变呈交替变化;异步轧制板材在压下量达到24%左右时,表现出了良好的塑性变形能力,抗拉强度达到309MPa,峰值应变达到0.163。     

AZ31镁合金挤出板降温热轧的组织和织构的演变

研究AZ31镁合金挤出板坯在降温热轧过程中的组织和织构的演变规律.结果表明:退火前滑移和孪生是主要的变形机制和取向硬化机制;退火后长条晶的滑移和细小等轴晶晶界扩散迁移的共同作用成为主要的变形机制;随着压下量的增大,析出物开始破碎和分散,压下量在70%～80%之间时,基面织构组分的取向密度存在突变最大值,形成硬取向较强的{0001}基面织构,软化退火能大幅减弱硬取向;通过一道67%大压下量和一次软化退火可顺利地将AZ31镁合金轧制成厚0.5 mm的薄板.     

Effect of Extrusion Strain Path on Microstructure and Properties of AZ31 Magnesium Alloy Sheet

The mechanical properties of AZ31 magnesium alloy sheets processed by different extrusion strain paths were examined in correlation with concurrent microstructure and texture evolution. The conventional extrusion(CE) and asymmetric extrusion(ASE) paths were performed on Mg alloy sheets. The textures at near surface and mid-layer of ASE sheets were various throughout sheet thickness direction as a result of extra asymmetric shear strain. This can stimulate the orientation of(0002) basal planes to incline approximately 12° toward the shear direction. Moreover, the basal texture of ASE sheet was weakened compared with CE one. Enhancing the ambient formability of extruded Mg alloy sheet fabricated by ASE path was accomplished by the tilted weak basal texture.     

Microstructure and mechanical properties of a basal textured AZ31 magnesium alloy cryorolled at liquid-nitrogen temperature

A strongly basal textured AZ31 magnesium alloy were cryorolled at liquid-nitrogen temperature at various strains. The microstructure and texture of the rolled sheets have been investigated using electron backscatter diffraction (EBSD) and X-ray diffraction. The microstructural and textural evolutions of the AZ31 magnesium alloy during cryorolling have been discussed. A lot of twins were observed in the rolled sheets. The influence of strain on the twin types and variant selection during cryorolling for the magnesium alloy has been discussed quantitatively based on the orientation data collected using EBSD. The influence of the twins on the microstructural and textural evolutions for the AZ31 magnesium alloy during cryorolling has also been discussed. The mechanical properties of the cryorolled sheets were tested by uniaxial tensile tests at the ambient temperature with a strain rate 10^-3s^-1 in the tensile direction respectively along the rolling and transverse directions of the rolled sheets. The relationships between the mechanical properties and microstructure of the cryorolled sheets have been discussed in the present work. The active twinning during rolling at that cryogenic temperature has been found to play an important role in influencing the microstructure, texture, as well as the mechanical properties of the AZ31 magnesium alloy.     

Microstructure and texture evolution of AZ31 magnesium alloy during rolling

The production of magnesium alloy sheets normally involves several processing stages including hot rolling,cold rolling and intermediate annealing.The microstructure and texture evolution of AZ31 magnesium alloy sheets in different processing states were investigated by optical microscopy and X-ray diffraction technique.It is found that the microstructure of hot-rolled sheets is dominated by recrystallized equiaxed grains,while that of cold-rolled sheets is dominated by deformation twins.With final annea...     

Effect of deformation mode,dynamic recrystallization and twinning on rolling texture evolution of AZ31 magnesium alloys

In order to obtain quantitative relationship between (0002) texture intensity and hot rolling conditions, conventional rolling experiments on AZ31 magnesium alloys were performed with 20%–40% reductions and temperatures within the range of 300–500 °C. Shear strain and equivalent strain distributions along the thickness of the rolled sheets were calculated experimentally using embedded pin in a rolling sheet. Rolling microstructures and textures in the sheet surface and center layers of the AZ31 alloys were measured by optical microscopy (OM), X-ray diffractometry (XRD) and electron back scatter diffraction (EBSD). Effects of the rolling strain, dynamic recrystallization (DRX) and twinning on the texture evolution of the AZ31 alloys were investigated quantitatively. It is found that the highest (0002) basal texture intensities are obtained at a starting rolling temperature of 400 °C under the same strain. Strain–temperature dependency of the (0002) texture intensity of the AZ31 alloy is derived.     

Cold stamping for AZ31B magnesium alloy sheet of cell phone house

Electric product house of magnesium alloy sheet is usually obtained by warm stamping owing to its poor plasticity and formability at room temperature. The formability of AZ31B magnesium alloy sheet can be improved by repeated unidirectional bending (RUB) process through control of (0002) basal texture. Compared with as-received sheet, the Erichsen value (IE) of the sheet underwent RUB process increases to 5.90 from 3.53 at room temperature. It is also confirmed that cell phone houses could be stamped successfully in crank press with AZ31B magnesium alloy sheets underwent RUB process. It provides an alternative to the electronics industry in the application of magnesium alloys.