AZ31镁合金薄板经不同累积应变的连续弯曲变形后的显微组织与成形性能（英文）

对AZ31镁合金板材进行不同累积应变的连续弯曲变形及退火处理,随后对显微组织与力学性能的变化进行了研究。结果表明:经不同累积应变的连续弯曲变形后,镁合金板材的显微组织中没有发现孪晶,退火后,板材表层的晶粒异常长大,粗晶层的厚度随着累积应变的增加而增加,并且镁合金板材的织构朝RD方向偏转,偏转角度随累积应变的增加而增大;与原始板材相比,连续弯曲变形及退火处理使镁合金板材呈现出较好的室温成形性能(杯突值由2.3 mm提高到4.9 mm,提高了~113%),这主要归因于基面织构的改善使镁合金板材的r值减小与n值增大。     

显微组织和织构对AZ31B镁合金成形性能的影响(英文)

通过单向多道次弯曲(RUB)工艺及随后的退火处理来改变镁合金的显微组织和织构,研究显微组织和织构对其成形性能的影响。RUB工艺和不同温度下的退火处理对显微组织有两方面的影响:粗化晶粒和削弱织构。经RUB处理并在300°C退火的板材表现出最好的成形性能。这主要归因于(0002)基面织构强度的削弱,而织构的削弱导致了较低的屈服强度、较大的断裂伸长率、较小的Lankford值(r值)和较大的加工硬化指数(n值)。与原始板材相比,经RUB处理并在400°C退火而产生的具有粗大晶粒的板材具有较低的拉伸性能,但却表现出较高的成形性能。这主要是由于粗大晶粒增强了变形孪晶,而变形孪晶可以协调厚向应变。     

AZ31镁合金板材经过连续弯曲变形后显微组织和成形性能的变化（英文）

通过采用连续弯曲(CB)工艺来改善AZ31镁合金板材的成形性能。通过光学显微镜(OM)和电子背散射技术(EBSD)研究镁合金板材的显微组织和织构的变化。结果表明:经过CB处理并退火后基面织构强度明显削弱;第一道次弯曲在内表面产生大量的孪晶,由于在第二道次过程中发生退孪生,孪晶密度明显下降;由于V形弯曲时内侧和外侧拉压应变状态的不对称性,连续弯曲过程中孪生-退孪生交替出现;与原始板材相比,经过连续弯曲处理板材的杯突值为5.2 mm,提高了41%,这主要是由于基面织构的弱化,以及织构弱化导致的较小的塑性应变比(r值)和较大的加工硬化指数(n值)。     

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。     

异步轧制AZ31镁合金的微观组织与室温成形性能

探讨采用小异速比多道次异步轧制技术提高AZ31镁合金板材室温成形性能的可行性,研究异步轧制板材微观组织的特点、形成机理及其与成形性能间的内在联系。结果表明:多道次异步轧制所累积的剪切应变能有效促进压缩孪晶的交互作用,细化合金晶粒组织,削弱(0002)基面的织构强度;异步轧制AZ31镁合金板材后续退火处理后的室温伸长率和Erichsen值分别可达32%和6.14mm;(0002)基面织构减弱和塑性应变比的降低是板材室温成形性能提高的根本原因。     

不同终轧压下量下AZ31镁合金板材的微观组织与力学性能研究

研究了高温轧制、不同压下量(10%～20%)下AZ31镁合金板材的微观组织、织构、力学性能与室温成形性能演变。结果表明,对于轧制态板材而言,不同压下量的板材中孪生仍然是主要变形模式,这主要是由终轧道次压下量相对较小,不足以引起动态再结晶但足以引起孪生导致。与终轧压下量10%的板材相比,20%的轧制板材表现出较大的晶粒尺寸和较弱的基面织构强度。退火后,板材表现出基轴向RD方向偏转±9.6°～±12°的双峰织构特征。与轧制态相比,退火态的基面织构显著弱化,这主要是由于板材在退火过程中的静态再结晶作用。随着终轧压下量由10%增加至20%,退火板材的基面织构显著减弱,使其r值降低、n值增大,从而引起板材室温杯突值由4.3 mm提高为6.3 mm。     

AZ31镁合金板弯曲限宽矫直增厚预置拉伸孪晶

采用弯曲限宽矫直增厚技术在具有强基面织构的原始AZ31 镁合金轧制板中预置拉伸孪晶,研究了弯曲限宽矫直处理前、后镁合金中微观组织和织构的演变及力学性能的变化.结果表明:弯曲限宽矫直处理后合金中的强基面织构被消除,转化为RD方向偏转织构,获得含量为22％的拉伸孪晶界,晶粒尺寸由(11±3)μm减小为(6.4±4)μm;再经过300℃×60 min退火处理后,RD偏转织构强度峰值由7.4降为6.0,晶内仍保留大量拉伸孪晶,晶粒尺寸增加到(7.7±4)μm,其断后伸长率为13.5％,屈强比由轧制态0.63 降至0.32,有利于改善塑性,提升镁合金板材的成形性能.     

轧制-剪切-弯曲变形AZ31镁合金板材的表面质量缺陷与机理研究

通过分析轧制-剪切-弯曲AZ31镁合金板材的裂纹特征,并采用有限元数值模拟和金相观测,研究了不同通道间隙下AZ31镁合金板材表面质量缺陷与应力、应变、模具弯曲半径、微观组织结构的关系。结果表明:板材易在第2弯曲转角处出现非连续横向裂纹,同时模具进口平面处板材易发生连续的起皱现象;随着通道间隙的增大,模具转角处应力、应变值逐渐变小,网格畸变程度逐渐降低,同时第2弯曲转角半径的增大也有利于制备出表面质量良好的AZ31镁合金板材;由于轧制、剪切、弯曲变形的应力、应变积累过大,裂纹主要出现在剪切带相对集中、孪晶交叉较多的区域,裂纹的拓展主要在孪晶界附近。     

AZ31镁合金板材低温双向反复弯曲变形及退火过程的组织演化

对AZ31镁合金热轧板材在423 K进行了双向反复弯曲变形及523 K退火处理,利用OM及SEM/EBSD技术研究了该工艺过程中的组织和织构演化规律.结果表明,孪生为其主要的变形机制,随着变形道次的增加,靠近表面的晶粒中不断地累积孪生变形,并最终被高密度的孪晶分割细化;而中部组织变化不大,仅有少量孪晶产生;样品趋向于形...     

轧制工艺对铸轧AZ31镁合金板材组织的影响

观察了铸轧AZ31镁合金板材经不同异步比轧后试样的显微组织。结果表明,与同步轧制相比,异步轧制能显著降低AZ31镁合金的动态再结晶温度,细化晶粒,并且提高其低温轧制时的成形能力,无需中间退火处理即可制备出最终厚度为0.7 mm的镁合金薄板。同时,异步轧制能够明显减弱板材的基面织构,但其强度并不随异步比增加呈现明显的单调递减规律。     

Influence of Continuous Bending Process on Texture Evolution and Mechanical Properties of AZ31 Magnesium Alloy

Mg–3Al–1Zn alloy sheets have been deformed by continuous bending(CB) to investigate the effects of pro cessing parameters(bending angle and repetitive passes) on the texture and formability. The samples exhibited a bimoda microstructure with abnormal growth grains in the surface region and fine grains distributed in the center after CB process followed by annealing. The texture evolution measured by XRD indicated that the basal poles were rotated from ND toward RD, and the texture intensity decreased with the bending angle decreasing and repetitive passes increasing Compared with the as-received sample, the yield strength of CBA-120-2 sample significantly decreased from 183 to112 MPa, and a smaller r-value and a larger n-value were obtained. The formability of CB processed samples in annealing condition was significantly enhanced with the highest of Erichsen value of 5.4 mm, increased by about 135%. The improvement of formability was likely attributed to the weakened and RD-tilt basal texture and coarse grains in the surface part.     

Effect of Pre-stretch Strain at High Temperatures on the Formability of AZ31 Magnesium Alloy Sheets

High-temperature pre-stretching experiments were carried out on the AZ31 Mg alloy at 723 K with strain levels of 2.54%, 6.48%, 10.92%, and 19.2% to alter the microstructure and texture for improving room-temperature formability. The results showed that the strain-hardening coefficient increased, while the Lankford value decreased. In addition, the Erichsen values of all pre-stretch sheets were enhanced compared with that of the as-received sheet. The maximum Erichsen value increased from 2.38 mm for the as-received sample to 4.03 mm for the 10.92%-stretched sample, corresponding to an improvement of 69.32%. This improvement was mainly attributed to the gradual increase in grain size, and the (0001) basal texture was weakened due to the activated non-basal slip as the high-temperature pre-stretching strain levels increased. The visco-plastic self-consistent analysis was performed on the as-received and high-temperature pre-stretched samples. Results confirmed the higher activity of the prismatic slip in 10.92%-stretched sample, leading to divergence and weakening of basal texture components. This results in an augmentation of the Schmid factor under different slip systems. Therefore, it can be concluded that high-temperature pre-stretching technology provided an effective method to enhance the formability of Mg alloy sheets.     

Influence of initial texture on formability of AZ31B magnesium alloy sheets at different temperatures

Repeated unidirectional bending (RUB) process was carried out to improve the texture of AZ31B magnesium alloy sheets. Influence of initial texture on formability of AZ31B magnesium alloy sheets at different temperatures was investigated. Compared with the as-received sheets, the limiting drawing ratio of the RUB processed sheets increased to 1.3 at room temperature, 1.5 at 50 °C and 1.7 at 100 °C, respectively. The improvement of the press formability at lower temperatures can be attributed to the texture modification, which led to a smaller Lankford value and a larger strain hardening exponent. However, the press formability of the sheet with a weakened basal texture has no advantage at higher temperature. This is due to much smaller r-value that results in severe thinning in thickness direction during the stamping process which is unfavorable to forming. Anyhow it is likely that the texture control has more effect on the press formability at lower temperature.     

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.     

Tailoring the Texture and Mechanical Anisotropy of Multi-cross Rolled Mg-Zn-Gd Alloy by Annealing

The unidirectional rolled Mg-Zn-Gd sheet usually exhibited non-basal texture with two peaks whose tilting angle were about 42° from normal direction to transverse direction (TD), which would cause the mechanical anisotropy. In this study, multi-cross rolling followed by annealing was used to tailor the texture and mechanical anisotropy for Mg-Zn-Gd alloy. With increasing annealing temperature, the rolled basal texture with two peaks gradually transformed into the circle texture with multi-peaks. In order to figure out different texture components evolution during annealing, the basal texture, R-texture and T-texture component were defined and studied. The results showed that the change of R-texture and T-texture component was asynchronous with increasing annealing temperature from 250 to 400 °C. The tilting angle of R-texture component increased slightly, while the tilting angle of T-texture component increased obviously, and this phenomenon was attributed to the preferential nucleation at grain nucleation stage rather than preferential grain growth. The yield strength along TD was more sensitive to annealing temperature compared with that along rolling direction (RD), resulting in different descending slopes and yield strength anisotropy with increasing annealing temperature. Annealing at 300 °C was the best annealing temperature due to low yield strength anisotropy, moderate strength and good elongation among these annealing temperatures. The Schmid factor for basal slip indicated that the activity of basal slip along RD increased slightly, while that along TD increased obviously with increasing annealing temperature from 250 to 400 °C, which should be caused by the asynchronous change of R-texture component and T-texture component, consequently resulting in the transformation from isotropic yield strength to anisotropic yield strength.     

Microstructure and mechanical properties of AZ31 magnesium alloy sheets produced by differential speed rolling

The as-extruded AZ31 alloy sheets of 10 mm in thickness were subjected to differential speed rolling (DSR) process performed on a mill, of which the rotation speed ratio of the lower roll and upper one is kept at constant 1.05 by using the different upper and lower roller diameters. The influence of the billet temperature, pass and total thickness reduction ratio on the microstructures, mechanical properties and crystal orientation of the specimens were examined by optical microscopy, tensile test and X-ray diffraction. The present process was found to be effective to refine the grain size and restrain the twinning. Grain refinement became more marked and uniform when the pass and total thickness reduction ratio increased, and the sheets processed by DSR exhibited higher elongation and lower strength than those of the conventional rolled sheets under the same testing conditions. Especially, the AZ31 sheet with elongation of 32% at room temperature was prepared. Moreover, anisotropy was diminished by further annealing at 573 K for 30 min. The DSR does not alter the basal texture but leads to the incline of the basal plane from the sheet surface plane to some extent.     

Improvement of stretch formability of Mg-3Al-1Zn alloy sheet by high temperature rolling at finishing pass

The effects of increasing rolling temperature from 723 K to 828 K at the last rolling pass on microstructure, texture, mechanical properties and stretch formability of a Mg-3Al-1Zn magnesium alloy previously rolled at 723 K were investigated. In the as-rolled condition, the basal texture strengthens slightly with increasing the rolling temperature whereas it weakens more remarkably after static recrystallization during annealing for the sheets rolled at higher temperatures. Only by increasing the rolling temperature from 723 K to 798 K, the Erichsen value is significantly increased from 4.5 to 8.6 due to the weakened texture for the annealed sheets. Further increasing the last rolling temperature does not appear to further improve the stretch formability.     

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...     

Improvement of Drawability at Room Temperature in AZ31 Magnesium Alloy Sheets Processed by Equal Channel Angular Rolling

A new rolling process, so-called as equal channel angular rolling (ECAR) process, for fabricating the magnesium alloy sheets with an enhanced formability at room temperature is introduced. The ECAR device was designed so that it could feed the sheet with the preheated temperature of 673 K in a continuous manner at a relatively high speed of 0.43 m/s. A significant amount of the shear deformation could be achieved by passing the sheet through the mold with the oblique angle of 115°. The x-Ray spectra were examined to analyze the crystal orientation of the sheets, which indicates that the crystal orientation with non-basal plane was fabricated after ECAR processing. The grain was not refined and plenty of twins were brought out because of the low-shear deforming temperature. The high stress and low ductility for the ECARed specimens can be related to the presence of twins. In spite of having the similar optical microstructure, the elongation to failure for the ECARed specimens after annealing was above 33%, which was larger than that of about 20% for the as-received/annealed specimens. And the drawability for the ECARed/annealed specimens with the Erichsen value of 6.24 mm and the limiting drawing ratio of 1.6 can be obtained, which is improved dramatically than that of 4.18 mm and 1.2 for the as-received/annealed specimens, respectively. These can be related to the rotation of (0002) basal plane toward the rolling direction because of the shear deformation induced by ECAR process.     

Effect of initial textures on texture formation in AA 3004 sheets during continuous confined strip shearing and subsequent annealing

The effect of initial textures on the texture formation during continuous confined strip shearing (CCSS) and subsequent annealing was investigated in AA 3004 sheets. The CCSS tools were designed to provide a constant shear strain of the order of 0.5 per pass while preserving the original sheet shape. During the CCSS deformation, the initial texture disappeared, and shear texture components developed. However, the intensity of the shear texture components did not further develop with an increasing number of CCSS passes. The softer initial sample depicting the cube texture displayed the evolution of {111}//ND fiber orientations. Upon recrystallization annealing, the textures developed during CCSS were randomized through the suppression of oriented nucleation and selected growth which generally dominate the evolution of recrystallization texture in cold rolled aluminum alloy sheets.