Texture evolution of AA3003 aluminum alloy sheet produced by accumulative roll bonding

The accumulative roll bonding process was carried out on an AA3003 aluminum alloy sheet up to eight cycles. The electron backscattering diffraction (EBSD) method was employed to investigate the microtextural development in the ARB processed sheets. The results indicate that with increasing the number of cycles, the overall texture intensity increases even up to the eighth rolling pass and a strong texture develops. The main textural components are the copper and Dillamore components of which the intensities increase with increasing number of cycles. Measurement of microhardness and lamellar spacing of grains in the processed sheets revealed that the presence of second phase particles in this aluminum alloy can promote the occurrence of dynamic recovery during the ARB process.     

Microstructure and mechanical properties of Mg-5Li-1Al sheets prepared by accumulative roll bonding

Ultrafine-grain and high-strength Mg-5Li-1Al sheets were prepared by accumulative roll bonding (ARB) process. Evolution of microstructure and mechanical properties of ARB-processed Mg-5Li-1Al sheets was investigated.Results show that, during ARB process, the evolution of deformation mechanism of t Mg-5Li-1Al alloy is as follows: twinning deformation, shear deformation, forming macro shear zone, and finally dynamic recrystallization (DRX). The grain refining mechanism changes from twin DRX to rotation DRX. With the increase in ARB cycles, strength of the Mg-5Li-1Al sheets is enhanced, whilst elongation varies slightly. With the increase in rolling cycles, anisotropy of mechanical properties decreases. It is conclusive that strain hardening and grain refinement dominate the strengthening mechanism of Mg-5Li-1Al alloy.     

A Process of Notch Wavy Rolling for Strengthening Metal Sheets

Wavy roll design was employed for strengthening 1 mm thin austenitic stainless steel coil sheet by cold rolling without further reduction in thickness. This steel possesses high corrosion resistance and high ductility. Initially, the sheets were rolled into sine wave shape (wave amplitude <2 mm) and then flattened using conventional cold rolling mill. Such a process cycle was repeated for four times successfully and the mechanical properties were measured after each cycle. The yield strength increased from 255 to 931 MPa with corresponding decrease in elongation from 45% to only 17% after the fourth cycle of severe cold working. Tensile strength and hardness values increased from 753 MPa and 185 HV to 973 MPa and 371 HV, respectively. The micro-to-nano-scale resolution structures, obtained by optical and atomic force microscope (AFM), were used to explain the variation in properties during this manufacturing process and to propose schematically the deformation mechanism.     

Microstructure development and texture evolution of ME20 sheets processed by accumulative roll bonding

Magnesium alloy ME20 sheets were produced by accumulative roll bonding (ARB) up to 8 cycles. The rolling microstructure was significantly refined during the first 2 cycles and remained homogeneous up to 6 cycles. After 8 cycles (ε ~ 6.4) the homogeneous equiaxed microstructure was replaced by a very fine shear band microstructure. With increasing ARB cycles, the texture intensity of basal poles decreased leading to a higher sheet tensile strength but with decreasing ductility.     

Accumulative roll bonding of aluminum alloys 2219/5086 laminates: Microstructural evolution and tensile properties

The present study describes the course of microstructure evolution during accumulative roll bonding (ARB) of dissimilar aluminum alloys AA2219 and AA5086. The two alloys were sandwiched as alternate layers and rolled at 300 °C up to 8 passes with 50% height reduction per pass. A strong bonding between successive layers accompanied by substantial grain refinement (∼200–300 nm) is achieved after 8 passes of ARB. The processing schedule has successfully maintained the iso-strain condition up to 6 cycles between the two alloys. Afterwards, the fracture and fragmentation of AA5086 layers dominate the microstructure evolution. Mechanical properties of the 8 pas ARB processed material were evaluated in comparison to the two starting alloy sheets via room temperature tensile tests along the rolling direction. The strength of the 8 pass ARB processed material lies between that of the two starting alloys while the ductility decreases after ARB than that of the two constituent starting alloys. These differences in mechanical behavior have been attributed to the microstructural aspects of the individual layer and the fragmentation process.     

Property optimization of nanostructured ARB-processed Al by post-process deformation

The effect of post-process deformation on the mechanical properties of nanostructured aluminum (99.2% purity) has been investigated by cold rolling of samples which have been processed by accumulative roll bonding (ARB) to a strain of ε_vM = 4.8. Samples have been cold rolled to 10, 15, and 50% reductions and ultimate tensile strength (UTS), yield stress and elongation have been determined by tensile testing at room temperature. The mechanical testing shows that cold rolling to low strains (10% and 15%) leads to softening and increase in elongation compared to the as-processed ARB material. In contrary, cold rolling to large strain (50%) results in significant strengthening. This leads to the suggestion of a transition strain within the range of 25–35% reduction by rolling. The microstructural evolution during post-process deformation has been followed by transmission electron microscopy showing a significant change in the dislocation structure when the strain is increased. Based on the experimental observations the mechanical behavior is related to the structural changes focusing on the characteristics of the dislocation structure present between the narrowly spaced lamellar boundaries in the deformed structure.     

Solid-state amorphization of Cu + Zr multi-stacks by ARB and HPT techniques

A series of CuZr binary alloys with wide composition range were fabricated through ARB and HPT techniques using pure Cu and Zr metals as the starting materials. Bulk alloy sheets with thickness of about 0.8 mm after ARB process and alloy disks with 0.30 mm in thickness and 10 mm in diameter after HPT process can be obtained, respectively. The structures of all the alloys were found to be gradually refined with the increase of ARB cycles or HPT rotations. As a result, nanoscale multiple-layered structure was formed for the 10 cycled ARBed specimens, which could partially transform into amorphous phase during subsequent low temperature annealing. While for the as-HPTed sample, the alloy was completely amorphized after 20 rotations without any heat treatment. The thermal stabilities of the amorphous alloys were studied. The deformation behavior and the amorphization mechanism during the ARB and HPT process were put forward and discussed.     

Fabrication of nanostructured Al/Cu/Mn metallic multilayer composites by accumulative roll bonding process and investigation of their mechanical properties

Multilayered Al/Cu/Mn composites were produced from aluminum 1100 strips, commercial copper foils and manganese powders, through accumulative roll bonding (ARB). The structural and microstructural evolution of the produced composites was studied by X-ray diffraction and scanning electron microscopy. Also, their mechanical properties at various ARB cycles were studied by microhardness and tensile tests. In this process after nine ARB cycles, a multilayered Al/Cu/Mn composite with homogeneously distributed, fragmented copper layers and Mn powders in the aluminum matrix was produced. Also, it was observed that with increasing strain by progression of the ARB process, the strength and microhardness of the produced composites increased.     

Evolution of reinforcement distribution in Al–B4C composites during accumulative roll bonding

The distribution of reinforcement particles in the matrix of a composite is one of the most important microstructural features affecting properties. In this study, nanostructured Al–B₄C composite sheets were processed by accumulative roll bonding (ARB), and the effect of the number of ARB cycles on the distribution of the B₄C particles in the Al matrix was evaluated. From optical microscopic studies accompanied by the radial distribution function analysis, it was realized that the microstructure uniformity is improved by increasing the number of ARB cycles. It was in good agreement with bulk hardness measurements in which the standard deviation of the hardness values was decreased by progression of the ARB process. In addition, the X-ray diffraction peak profile analysis revealed that the area weighted mean crystallite size of the Al matrix decreases to the nanometric scale (114 nm) after seven ARB cycles.     

Texture development and microstructure evolution in metastable austenitic steel processed by accumulative roll bonding and subsequent annealing

In this paper, microstructure and texture development in a Fe–24Ni–0.3C metastable austenitic steel processed by accumulative roll bonding (ARB) and subsequent annealing was studied. Microstructural observations and crystallographic analysis were carried out by FE-SEM/EBSD. The results showed that elongated ultrafine-grained austenite having 300 nm in thickness surrounded by high angle boundaries was obtained after 6 cycles of the ARB process. It was found that 1-cycle ARB-processed specimen exhibited Copper ({112} 〈111〉) component as main texture, while by increasing the number of ARB cycles, it deviated to S component ({123} 〈634〉) at 2 cycles or Brass component ({110} 〈112〉) at 6-cycle. Annealing of 6-cycle ARB-processed specimen at 873 K for 1.8 ks resulted in the formation of an austenite with mean grain size of 2.5 µm having strong Cube recrystallization texture ({100} 〈001〉).     

Tailoring materials properties of UFG aluminium alloys by accumulative roll bonded sandwich-like sheets

Accumulative roll bonding (ARB) as a method of severe plastic deformation is a well-established process to produce ultrafine-grained (UFG) sheet materials with extraordinary mechanical properties. In this work ARB is applied to combine different sheet materials in order to tailor the materials properties by producing sandwich-like structures. The high strength aluminium alloy AA5754, after 4 ARB cycles (N4), is used as a core material. To achieve high corrosion resistance and good visual properties, it is cladded with commercially pure aluminium AA1050A (N4) at room temperature and alternatively with AA6014 (N4) at 230 °C. All materials are UFG and satisfactory bonding between the different layers of aluminium alloys is achieved. Nanoindentation measurements reveal that there is a sharp transition in hardness at the interface. The yield and tensile strength of the core material are fully retained in the case of the AA6014/AA5754 sandwich. The strength of the AA1050A/AA5754 sandwich is slightly lower compared to the core material but still twice as high as the clad material. The serrated yielding effect which is strongly visible in tensile tests on the pure AA5754 alloy completely disappears in the sandwich sheets, which means the surface quality is strongly enhanced.     

ARB (Accumulative Roll‐Bonding) and other new Techniques to Produce Bulk Ultrafine Grained Materials

Accumulative roll‐Bonding (ARB) is a severe plastic deformation (SPD) process invented by the authors in order to fabricate ultrafine grained metallic materials. ARB is the only SPD process applicable to continuous production of bulky materials. In the process, 50 % rolled material is cut into two, stacked to be the initial dimension and then rolled again. In order to obtain one‐body solid material, the rolling in ARB is not only a deformation process but also a bonding process (roll‐bonding). By repeating this procedure, SPD of bulky materials can be realized. In this review paper, various kinds of new SPD mechanical properties of the ARB processed materials are indicated.     

Role of second phase particles on microstructure and texture evolution of ARB processed aluminium sheets

Abstract

The accumulative roll bonding (ARB) process was carried out on a high purity alloy (AA1100) and a particle containing aluminium alloy (AA3003) for up to eight cycles. The electron backscattered diffraction (EBSD) method was utilised to investigate the microstructural and microtextural evolution in ARB processed sheets. The results indicate that the lack of second phase particles in pure aluminium hinders grain refinement and leads to the formation of unrefined bands, which results in the increase of the overall texture intensity and the development of a strong texture. A submicrometre grain structure in this alloy develops at the final stages of the process. It was also found that the presence of second phase particles in AA3003 alloy prevents the development of such unrefined bands and improves grain refinement during the ARB process, which results in a more homogenous microstructure of ultrafine grains.     

Microstructure and mechanical properties of Mg–Al–Zn alloy sheets severely deformed by accumulative roll-bonding

The as-rolled AZ31 Mg alloy sheets were subjected to accumulative roll-bonding (ARB) at 300 °C up to three cycles. The microstructure and macro- texture are investigated by means of optical microscopy and X-ray analysis. The mechanical properties are evaluated by micro-hardness and tensile tests. Very fine grain size of 2.4 μm could be achieved after three passes of 50% thickness reduction. The recrystallized structure was already formed after one cycle of ARB. ARB processing resulted in a significant increase of ductility and slight decrease of tensile strength of the AZ31 alloy sheet. Basal texture was notably weakened after ARB processing.     

变厚度区薄板轧制的辊缝设定模型与试验

为实现高精度的变厚度轧制,需要对变厚度轧制的厚度控制模型进行研究.基于离散化的控制思想和轧制弹跳方程建立了一种TRB变厚度区轧制辊缝设定模型,用于单机架可逆式四辊冷轧机厚度控制系统.研究了辊缝变化的非线性规律,基于误差分析提出了确定离散区间的方法;给出了一种TRB辊缝控制系统结构以及空载辊缝闭环和负载辊缝闭环的控制方程,并在实验四辊轧机上进行了单厚度过渡区的TRB轧制.结果表明,采用离散化的辊缝设定方法可以实现TRB板的50 mm变厚度区,尺寸最大厚度偏差为0.08 mm,长度偏差<1 mm.     

Analysis of through-thickness heterogeneities of microstructure and texture in nickel after accumulative roll bonding

The through-thickness heterogeneities of the microstructure and texture have been investigated in pure nickel processed by six cycles of accumulative roll bonding (ARB) with lubrication applied during each rolling pass. Strong rolling textures are found in the intermediate and center layers of the deformed sample, whereas increased fractions of the shear texture are observed near the surface. Significant differences at different depths are also revealed in the fractions of areas containing either predominantly low angle misorientations or predominantly high angle misorientations. It is found that the fractions of such areas are much more sensitive to the deformation history than the average parameters based on the measurements of the boundary spacing and fractions of high angle boundaries. For the material studied in this work, the area fraction of the low misorientation regions appears to correlate with the summed fraction of the rolling texture components. The observed microstructural and textural variations are discussed and compared with literature data, taking into account the influence of large-draught rolling and lubrication on the distribution of strain imposed during the ARB process.     

累积叠轧纯Mg/ZK60镁合金层状金属复合材料的组织与性能

采用累积叠轧技术在300℃下制备了纯Mg/ZK60 Mg合金多层复合板材。经过初始复合后,Mg层和ZK60层晶粒明显细化,随着循环次数的增加,Mg/ZK60复合板材两组元晶粒细化并不明显。两种组元的层厚随着循环次数的上升而逐渐降低,两次循环后Mg/ZK60复合板材出现波浪状组织。累积叠轧后,Mg/ZK60复合板材中Mg层和ZK60层呈现典型的轧制织构类型,{0001}基面均向轧制方向发生轻微偏转。Mg/ZK60复合板材的强度及延伸率均介于轧制态的ZK60板与Mg板之间,并随着循环次数的增加逐渐提高。Mg/ZK60复合板材室温阻尼性能和高温阻尼性能均介于纯Mg与ZK60之间,而高温下Mg/ZK60复合板材的高温阻尼则与ZK60板材变化趋势相类似。      

Development and characterization of Al/MWCNT–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> hybrid composite by accumulative roll bonding

A high-strength hybrid composite was produced by eco-friendly accumulative roll bonding (ARB) process. Multiwall carbon nanotubes and alumina layers as reinforcements were embedded in a matrix of aluminum 1100. The produced hybrid composite was evaluated for structural changes and mechanical properties. The structural micrographs showed that by increasing the rolling cycles, a more uniform distribution of the reinforcements is obtained. After ten cycles of ARB, the composite material reached strength of about 300% higher than that of the annealed aluminum 1100. The elongation of the composite material is decreased by adding reinforcements. However, at a constant value of reinforcements, the elongation slowly increased during sequential rollings. A shear ductile rupture type failure was responsible for fracture of tensile test specimens of both composite and monolithic specimens.     

Formability analysis of thin press hardening steel sheets under isothermal and non-isothermal conditions

Aiming at the enhancement of the lightweight potential of press hardening steels, investigations on the formability of thin, boron alloyed, hot dip aluminized steel sheets are carried out. The material formability is described through Forming Limit Diagram (FLD), determined by means of Nakajima formability test of thin 22MnB5 sheets (0.50 mm, 0.80 mm, 1.25 mm) at elevated temperatures. The influence of sheet thickness on forming limits is evaluated under both isothermal and non-isothermal conditions. The effect of different deformation start temperatures is examined. The non-isothermal behavior is further investigated via microstructural analysis and a study on temperature profile during Nakajima test. The results show a significant difference regarding the influence of sheet thickness under isothermal and non-isothermal conditions. Increasing the sheet thickness results, as expected, in higher forming limits for isothermal conditions, whereas for non-isothermal conditions the opposite effect on formability is observed. The obtained Forming Limit Curves (FLCs) are validated through hot stamping simulation and subsequent analysis of different thin components, concluding that in case of thin sheets the isothermal FLC constitutes a more conservative approach, while the non-isothermal one reaches the formability limits with higher accuracy.     

Unique mechanical properties of nanostructured metals

Recently, it becomes possible to fabricate bulk metals having ultrafine grained or nanocrystalline structures of which grain size is in nano-meter dimensions. One of the promising ways to realize bulk nanostructured metals is severe plastic deformation (SPD) above logarithmic equivalent strain of 4. We have developed an original SPD process, named Accumulative Roll Bonding (ARB) using rolling deformation in principle, and have succeeded in fabricating bulk nanostructured sheets of various kinds of metals and alloys. The ARB process and the nanostructured metals fabricated by the ARB are introduced in this paper. The nanostructured metals sometimes perform quite unique mechanical properties, that is rather surprising compared with conventionally coarse grained materials. The unique properties seem to be attributed to the characteristic structures of the nano-metals full of grain boundaries.