Microstructural evolution of twin-roll cast Mg–3Al–0.5Mn–0.2Mm alloys during warm rolling and subsequent annealing

Microstructure of twin-roll casted (TRC) Mg–3Al–0.5Mn–0.2Mm (or AM30 + 0.2Mm) alloy strips consisted of columnar dendrites in the surface and equiaxed dendrites in the center regions, as well as widely dispersed fine primary intermetallic compounds located in the interdendritic region. Warm rolling of the TRC strips developed both deformation or shear bands and homogeneously dispersed fine particles. No evident dynamic recrystallization (DRX) was found in the TRC sheets during warm rolling. The dispersed fine particles seemed to retard DRX. The warm-rolled TRC sheets showed equiaxed fine grains with an average size of around 8 μm after annealing at 350 °C for 60 min. The TRC sheets had superior yield and tensile strengths to ingot cast (IC) samples. Elongation was similar to both TRC and IC samples.     

成形过程对ZK60镁合金薄带组织和力学性能的影响

用OM,SEM,TEM和电子万能试验机对不同方法制备的ZK60镁合金薄带的组织和力学性能进行了研究.常规铸造ZK60镁合金轧制后仍为等轴晶组织,晶粒尺寸明显细化,双辊铸轧ZK60镁合金条带温轧变形后,显微组织由树枝晶转变为纤维状变形组织,且有高密度剪切带产生,温轧过程中没有明显的动态再结晶发生.轧制后两种合金均具有良好的力学性能,轧制态铸轧合金的强度明显高于传统铸造合金,伸长率略低于传统铸造合金.退火热处理后两种合金均发生了再结晶,得到等轴晶组织,且铸轧合金的组织比传统铸造合金的组织更加均匀细小.退火热处理使薄带的强度略有下降,而伸长率大幅度提高,退火后双辊铸轧合金和传统铸造合金的抗拉强度、屈服强度和延伸率分别为:388 MPa,301 MPa,22.9％和311MPa,219 MPa,19.3％.镁合金薄带制备过程的晶粒细化归因于剪切带、位错和挛晶的产生及后续退火过程中再结晶.     

Effect of Forming Process on Microstructure and

用OM, SEM, TEM和电子万能试验机对不同方法制备的ZK60镁合金薄带的组织和力学性能进行了研究。常规铸造ZK60镁合金轧制后仍为等轴晶组织,晶粒尺寸明显细化,双辊铸轧ZK60镁合金条带温轧变形后,显微组织由树枝晶转变为纤维状变形组织,且有高密度剪切带产生,温轧过程中没有明显的动态再结晶发生。轧制后两种合金均具有良好的力学性能,轧制态铸轧合金的强度明显高于传统铸造合金,伸长率略低于传统铸造合金。退火热处理后两种合金均发生了再结晶,得到等轴晶组织,且铸轧合金的组织比传统铸造合金的组织更加均匀细小。退火热处理使薄带的强度略有下降,而伸长率大幅度提高,退火后双辊铸轧合金和传统铸造合金的抗拉强度、屈服强度和延伸率分别为：388 MPa,301 MPa,22.9%和311 MPa,219 MPa,19.3%。镁合金薄带制备过程的晶粒细化归因于剪切带、位错和挛晶的产生及后续退火过程中再结晶。     

Warm deep drawing of wrought magnesium alloy sheets produced by semi-solid roll strip-casting process

This paper is concerned with the development of a continuous strip-casting technology to facilitate the manufacture of magnesium sheet alloys economically whilst maintaining high quality. Established in the paper is warm formability of cast magnesium alloy sheets after being hot rolled by semi-solid roll strip-casting process. It has been found that magnesium sheet with 2.0–4.0 mm thickness could be produced at a speed of 25 m/min. Hot rolling and annealing temperatures during hot rolling were also changed to examine which condition would be appropriate for producing wrought magnesium alloys with good formability. Microstructures of the crystals of the manufactured wrought magnesium alloys were observed. It has been found that a limiting drawing ratio of 2.7 was possible in a warm deep-drawing test of the cast magnesium alloy sheets after being hot rolled.     

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.     

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.     

Analysis of the solidification and deformation behaviors of twin roll cast Mg-6Al-X alloys

In this study, the solidification and deformation behaviors in twin roll cast (TRC) Mg-6Al-X alloys have been investigated. The TRC simulation results showed that the AX60 alloy tended to have lower segregation while the AZ60 had the highest segregation due to the different solidification behavior and thermal properties. Compared to the as-cast microstructure, the segregation area was well matched with the melt to roll nip distance predicted in simulation. Mg alloys with Ca or Sr elements showed weaker textures when compared to A6 alloys rolled at 350 °C. In addition, there was a significant change in (0002) pole figures from strong basal textures to random textures when the rolling temperature increased from 350 °C to 450 °C. This may be attributed to the non-basal slip system activity at high temperatures. The results of visco-plastic self-consistent simulation revealed that critical resolved shear stress of the tension twin increased with increasing rolling temperature. This led to tension twin suppression in compression, which were associated with enhancing the yield isotropy of Mg alloys. Furthermore, the relative activities of basal <a> slip in AX60 alloy were higher than the other Mg alloys. This means they were responsible for enhancing the formability and yield isotropy of Mg alloys.     

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 comparison of ZK60 alloy under casting, twin roll casting and hot compression

The microstructures of ZK60 alloy under conventional direct as-casting (DC),twin roll casting (TRC) and twin roll casting followed by hot compression (TRC-HC) were analyzed by optical morphology (OM),electron backscatter diffraction (EBSD) and X-ray diffraction (XRD).The deformation condition of hot compression is 350 ℃,0.1 s?1.The microstructural evolution under TRC-HC deformation followed by annealing at different temperatures and time was discussed.The results show that TRC provides more modified microstructure compared with DC.Twins are found in TRC processing;dynamic recrystallization (DRX),shear bands and twins are found in TRC-HC.A short annealing time has little effect on hardness,while during a long time annealing,it is found that low annealing temperatures increase the micro-hardness and high temperature decreases it.     

Friction and wear properties of steel backed Al-10Sn-4Si-1Cu metallic strips prepared via spray atomization-deposition-rolling route

In various load bearing structural applications related to automotive industries, steel backed aluminum alloy strips are considered. For such applications, it is desired to design appropriate alloy composition for metallic strip so that good tribological properties can be achieved. In our ongoing efforts to accomplish this aim, we have recently fabricated a steel backed Al-10Sn-4Si-1Cu bearing strip, which is prepared by spray depositing the molten bearing alloy on a steel substrate, followed by warm rolling of the resulting laminated strip to different thickness reductions up to 80%. The tribological performance of the steel backed Al-10Sn-4Si-1Cu strips is evaluated against the bearing steel. While the recorded steady state coefficient of friction (COF) does not show any noticeable difference (varying in the range of 0.6-0.7) with respect to difference in warm rolling conditions, the fretting wear rate (10-26 × 10^− 5 mm³ N^− 1m^− 1) of the steel backed and warm rolled strips exhibits a systematic decrease in wear rate with increase in amount of warm rolling. SEM-EDS analyses reveal the oxidative wear and the extensive cracking of alumina rich tribolayer as the dominant material removal mechanisms. The tribological properties of the spray deposited and 80% rolled steel backed Al-10Sn-4Si-1Cu bearing strip is compared with those of a commercially available Al-Sn based sleeve bearing under identical fretting conditions.     

Effect of Electromagnetic Field on the Micromorphology of Twin-roll Cast 7075 Alloy

利用电磁场的影响,生产铸轧合金板材,主要通过光学显微镜对7075合金的微观形貌和晶体尺寸进行研究。结果表明,同传统铸轧板材方式相比,670℃下交变振荡电磁场铸轧7075板材的枝晶严重被破坏,拉伸,细化和等轴化。同时,在静磁场条件下的铸板微观组织一定程度上细化和被拉伸,实验条件为励磁电流100 A。中心偏析带在直流磁场和交变振荡磁场条件下明显减轻,然而后者的影响效果更为突出。在表面和横截面处,7075板材硬度依次随着传统铸轧、静磁场铸轧和交变振荡磁场铸轧顺序增加。随着电磁强度增加,板材的强度和性能得到进一步改善。无论板材何处,升高温度都会使电磁场作用效果提高。     

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.     

Effect of rolling temperature on microstructure and texture of twin roll cast ZK60 magnesium alloy

Twin roll cast ZK60 alloy strip/sheet with final thickness of 0.5 mm was prepared,and effect of rolling temperature on microstructure and texture development was investigated using OM and XRD technique,microstructure and texture were measured on specimens subjected to rolling experiment at different rolling temperature,and macrotexture was also evaluated by X-ray diffraction method.In addition,the(1 010)and(0002) pole figures were measured,and the tensile test was performed to reveal the influence of rolling temperature on mechanical properties.The results show that the microstructure of ZK60 alloy sheet consisted of fibrous structure with elongated grains,and shear bands along the rolling direction after warm rolling.Dynamic recrystallization could be found during the warm rolling process at rolling temperature 350 °C and above.And many fine recrystallized grain could be observed in the shear bands area.It is a little difficult to see the recrystallized grain in the sheet warm rolled at 300 °C because of higher density of shear bands.The warm rolled ZK60 alloy sheet exhibited strong(0002) pole texture,the intensity of(0002) pole figure decreases with the increasing of rolling temperature and the basal pole tilted slightly to the transverse direction after warm rolling.     

Texture and mechanical properties of Al-0.5Mg-1.0Si-0.5Cu alloy sheets manufactured via a cross rolling method

The relationship between the texture and mechanical properties of 6xxx aluminum alloy sheets processed via cross rolling was investigated. The microstructures of the conventional rolled and cross rolled sheets after annealing were analyzed using optical micrographs (OM). The texture distribution across the thickness in the Al-Mg-Si-Cu alloy, conventional rolled sheets, and cross rolled sheets both before and after annealing was investigated via X-ray texture measurements. The texture was analyzed in three layers from the surface to the center of the sheet. The β-fiber texture of the conventional rolled sheet was typical of the texture obtained using aluminumoll ring. After annealing, the typical β-fiber orientations were changed to recrystallization textures: cube{001}〈100〉 and normal direction (ND)-rotated cubes. However, the texture of the cross rolled sheet was composed of an asymmetrical, rolling direction (RD)-rotated cubes. After annealing, the asymmetrical orientations in the cross rolled sheet were changed to a randomized texture. The average R-value of the annealed cross rolled sheets was higher than that of the conventional rolled sheets. The limit dome height (LDH) test results demonstrated that cross rolling is effective in improving the formability of the Al-Mg-Si-Cu alloy sheets.     

ASR work roll shifting strategy for schedule-free rolling in hot wide strip mills

In order to meet the requirement of schedule-free rolling (SFR) for wide non-oriented electrical steel production with a large number of the same width strip rolling campaigns, ASR (asymmetry self-compensating work rolls) shifting strategies for different rolling schedules are studied. According to the actual rolling process, the work roll wear prediction mathematical model for non-oriented electrical steel sheets and a 3D finite element model for roll stacks are established. The effects of the shifting step and the shifting rhythm on the ASR wear contour and the loaded roll gap profile within the entire rolling campaign are analyzed. The reasonable ASR shifting strategies for different rolling schedules are developed. In comparison with the conventional work roll contour of K-WRS mill, the self-maintenances of roll contours for ASR reach to more than 88%, the rate of the measured strip crown less than 45 μm increased from 41.8% to 94.9%, and the rate of the measured strip crown larger than 52 μm decreased from 32.6% to 2.0% by industrial test on the production of the same strip-width for wide non-oriented electrical steel sheets in the 1700 mm hot strip mill of WISCO. The ASR technology has applied to the production successfully.     

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.     

Effect of rolling and annealing processes on the hardness and electrical conductivity values of Cu-13.5%Mn-4%Ni alloy

It was found that the dendritic microstructure of an as-cast alloy was changed to an almost equiaxed alloy after 480 min of annealing at 700 °C. The electrical conductivity of as-cast and hot rolled samples increased from 27.36 and 30.51% IACS to 30.67 and 32.1% IACS after 480 min of annealing at 700 °C. The dendritic microstructure and the electrical conductivity values of an as-cast alloy annealed for 60 min remained almost unchanged when the annealing temperature was increased to 800 °C. The hardness values of the samples that were hot rolled and annealed for 60 min were higher than those of the as-cast samples for all annealing temperatures. The electrical conductivity values of the hot rolled and as-cast samples were almost the same after annealing at 800 °C for 60 min. It was shown that after 20% cold work, the electrical conductivity value of the as-cast sample decreased from 30.5% IACS to 22.6% IACS. The electrical conductivity values of the samples were not significantly changed when the cold work was increased from 20% to 60%. The electrical conductivity values of the 20%, 40% and 60% cold worked samples increased from 22.62, 24.69 and 26.63 to 27.14,28.36 and 30.55% IACS, respectively, after 30 min annealing at 400 °C.     

Development of efficient production routes based on strip casting for advanced high strength steels for crash-relevant parts

Twin roll strip casting can be an effective alternative to produce high manganese TWIP steel, which provides extraordinary mechanical properties. In the work presented, 1.5–3 mm thin hot strips with up to 30 wt% manganese were produced directly from the melt and further processed to cold strip. An adapted thermo-mechanical treatment, consisting of cold rolling with or without subsequent annealing, enables to adjust different material states, such as recrystallised or strengthened state, and thus to tailor the mechanical properties. As an example for the superior crash behaviour of high manganese TWIP steels, dynamic crash tests were carried out using cold rolled Fe–29Mn–0.3C steel in different material states.     

Electron back scattered diffraction (EBSD) characterization of warm rolled and accumulative roll bonding (ARB) processed ferrite

An interstitial free (IF) steel was severely deformed using accumulative roll bonding (ARB) process and warm rolling. The maximum equivalent strains for ARB and warm rolling were 4.8 and 4.0, respectively. The microstructure and micro-texture were studied using optical microscopy and scanning electron microscopy equipped with electron back scattered diffraction (EBSD). The grain size and misorientation obtained by both methods are in the same range. The microstructure in the ARB samples after 6 cycles is homogeneous, although a grain size gradient is observed at the layers close to the surface. The through thickness texture gradient in the ARB samples is different from the warm rolled samples. While a shear texture (〈1 1 0〉//rolling plane normal direction (ND)) at the surface and rolling texture at the center region is developed in the ARB samples, the overall texture is weak. The warm rolled samples display a sharp rolling texture through the thickness with increasing the sharpness toward the center. These differences are attributed to the fact that the central region of ARB strip is comprised of material that was once at the surface. The ARB process can suppress the formation of shear bands which are conventional at warm rolled IF steels. EBSD study on the sample with 6th cycle of ARB following the annealing at 750 °C verified a texture gradient through the thickness of the sheet. The shear orientations at the surface and at the quarter thickness layers can be identified even after annealing. The overall weak texture and existence of shear orientations make ARB processed samples unfavorable for sheet metal forming in compare with warm rolled samples.     

Microstructure and mechanical behavior of a Ti-24Nb-4Zr-8Sn alloy processed by warm swaging and warm rolling

A combination processing technique of warm swaging and warm rolling is proposed to refine grains and improve the mechanical properties of a multifunctional β-type Ti-24Nb-4Zr-8Sn (wt.%) alloy. The results show that a highly swirled marble-like microstructure can be easily produced by warm swaging at an initial temperature of 573 K, whereas it has little effect on the nonlinear elastic deformation compared with the hot forged alloy with an equiaxed microstructure. Although the swirled microstructure has the limitation of an inhomogeneous distribution, swaging has the great advantage of refining the initial subgrains produced by hot forging with little loss of ductility. The following warm rolling at an initial temperature of 673 K results in a uniform microstructure comprising β phase with a size less than ∼200 nm and the precipitation of nanosized α phase. Therefore, significant grain refinement was achieved through the formation and refinement of the subgrains. The ultrafine grained alloy exhibits large scale nonlinear deformation behavior with a recoverable strain of up to ∼3.4% in combination with a high strength of ∼1150 MPa, a low elastic modulus of ∼56 GPa and good ductility of ∼8%. Such an improvement in mechanical properties indicate great potential for biomedical applications.