Cross Accumulative Roll Bonding Research Articles

Enhancing grain refinement and mechanical properties of AA1100/MgAZ31/AA1100 composites by using different roll bonding techniques

This paper examines the microstructure and mechanical properties of AA1100/Mg AZ31/AA1100 composites processed by conventional accumulative roll bonding (ARB) and cross accumulative roll bonding (CARB) methods. Based on the results, with an increase in deformation strain, Mg layers gradually lose their continuity in the form of localized necking and fragmentation. However, changing the strain path and pre-annealing the initial sheets could retard and homogenize the plastic instabilities. According to the results of electron back-scattering diffraction (EBSD), applying severe plastic deformation led to refined-grain structures with equiaxed grains. The finer grains were obtained in composites processed by the CARB method following the pre-annealing treatment. Employing this procedure also intensified the basal-type texture and circled its shape. The strong basal texture and grain refinement led to the highest Mg alloy and Al hardness values of 99 and 64 HV, respectively. Furthermore, changing the strain path and pre-annealing treatment increased the elongation by 46% in the seventh pass compared to ARBed samples. Also, this procedure increased the ultimate strength from 375 to 391 MPa and gave rise to yield strength from 164 to 176 MPa.

Improving strength-ductility synergy of nano/ultrafine-structured Al/Brass composite by cross accumulative roll bonding process

Increasing the strength of metallic multilayered composites fabricated through accumulative roll bonding (ARB) is typically accompanied by a sacrifice in ductility. In the current work, we propose a strategy to achieve microstructural refinement and outstanding strength-ductility synergy in Al/Brass composites. Here, the aluminum matrix exhibits a bimodal grain distribution, consisting of fine equiaxed grains with an average size of ∼100 nm and ultrafine-elongated grains, in which the brass fragments were distributed uniformly. These microstructural features, introduced through cross accumulative roll bonding (CARB), provide synergistic strengthening effects. The CARB processed composite exhibits a mean misorientation angle of 43.16° and a fraction of high angle grain boundaries of 87%, compared to values of 38.02° and 79% for ARB processed specimen. The CARB processed composite demonstrates a major texture characterized by prominent Rotated Brass {110}<556>, Rotated Goss {011}<011>, and Rotated Cube {001}<110> components. In contrast, the ARB processed specimen revealed strong Goss {011}<100>, Rotated Goss {011}<011>, Brass {011}<211>, and S {123}<634> components. The Copper {112}<111> and S {123}<634> components were nearly absent in the CARB processed composite, because both of them were unstable under the CARB regime. The CARB processed composite shows a tensile strength of 405 MPa and a remarkable elongation of 12.4% at ambient temperature, outperforming ARB processed specimen with a tensile strength of 335 MPa and elongation of 9.5%. These unique mechanical properties in the CARB processed composite are ascribed to the dislocation strengthening, bimodal grain size distribution, uniformity of the brass fragments, and quality of bonding at the interfaces.

Enhancement of strength and ductility in 6061Al alloy processed by cross accumulative roll bonding

To achieve a good match between strength and ductility, plates of 6061 Al alloy were prepared by cross accumulative roll bonding (CARB) at ambient temperature for up to 7 cycles. The microstructures were analyzed by X-ray diffraction, transmission electron microscopy, scanning electron microscopy and electron backscatter diffraction. The results show that both the ultimate tensile strength and elongation of the CARB specimens are significantly better than those of ARB. Grain size of the samples processed by CARB is smaller, and more low-angle grain boundaries transform into high-angle grain boundaries. Also, the dislocation density in the CARB sample is higher. The rolling texture of the 6061 Al alloy processed by CARB is obviously weakened, and the Brass {011}〈211〉 texture is the main one. The higher strength of CARB 6061 Al alloy is mainly dominated by fine grain strengthening and dislocation strengthening, while the higher ductility is due to the finer grains and weak texture.

Microstructure, Mechanical and Thermal Properties of Al/Cu/SiC Laminated Composites, Fabricated by the ARB and CARB Processes

The aim of the current work is to investigate the effect of SiC particle weight percent and rolling passes on Al/Cu/SiC laminated composites, fabricated by accumulative roll-bonding (ARB) and cross-accumulative roll-bonding (CARB) processes. The optical microscopy (OM) images of composites revealed that despite the good bonding of the layers, they underwent plastic instabilities as a consequence of strain hardening of the layers. However, these instabilities occurred more in ARBed composites than in composites fabricated by the CARB process. This is because in the latter process, the composites are rolled in two directions, which leads to better strain distribution. Furthermore, with an increase in passes, SiC particles were well distributed in the matrix and interfaces. The mechanical findings showed that, by increasing passes, there was a growth in the values of strengths and elongation. This behavior is believed to be related to increased work-hardening of layers, better distribution of reinforcing particles, and an enhanced bonding of interfaces at higher rolling passes. In addition, the results of thermal conductivities showed a downward trend with an increase in passes; in fact, the increased number of Al/Cu interfaces declined the heat conduction of composites.

Microstructure evolution and mechanical properties evolution of high-Zn Al-Zn alloys prepared by cross accumulative roll bonding combined with heat treatment process

The cross accumulative roll bonding (CARB) combined with the heat treatment process was used to develop high-Zn Al-xZn alloys with 20 and 50 wt% Zn. The effect of the Zn content and fabrication process on the microstructural evolution, microhardness, tensile, and wear behaviors was investigated by using scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectrometry (EDS), microhardness indentation, uniaxial tensile, and wear testing (pin-on-disk) at room temperature. The microstructure of the Al-20 wt% Zn alloy featured α-Al granular structures, whereas by Zn content increasing to 50 wt% the structure was α + η eutectoid structures with a fine distribution. The increase of the Zn element from 20 to 50 wt% was accompanied by a significant increase in tensile strength and also microhardness, but reduction in the elongation percentage of the Al–xZn alloys. Additionally, the wear resistance was improved as the Zn content was increased from 20 to 50 wt%. Finally, mechanical results confirmed that by increasing Zn content in the developed alloys the mechanical properties improved.

Consideration on zinc content on the microstructure, mechanical, and corrosion evolution of aluminum/zinc composites fabricated by CARB process

Aluminum/zinc laminated composites with different zinc contents (20 and 50 wt%) were fabricated in the form of sheets by using cross-accumulative roll bonding (CARB) process. Microstructural investigations by scanning electron microscopy showed the properly uniform distribution of thin zinc layers in the aluminum matrix in both laminated composites. The mechanical properties of the specimens were investigated by tensile, wear, and micro-hardness tests. Tensile results revealed that by increasing the zinc content, tensile strength is improved from about 275 MPa for 20 wt% zinc to about 350 MPa for 50 wt% zinc after the 8th cycle of CARB. Wear tests in the different zinc contents showed that the variation of the wear rate versus the number of rolling cycles has a similar behavior in both zinc contents. However, wear resistance was improved by increasing the zinc content in the laminated composites. Electrochemical corrosion tests were also carried out on both composites at different cycles. The results reflected that the composite samples containing 20 wt% zinc have better corrosion properties in comparison to that with 50 wt% zinc content at different cycles. In conclusion, this study pointed out the potential of aluminum/zinc laminated composites fabricated by CARB for further development.

The effects of interfaces stability on mechanical properties, thermal conductivity and helium irradiation of V/Cu nano-multilayer composite

Interface engineering is a significant strategy to develop structural materials with good properties. In this study, bulk V/Cu nano-multilayers with different layer thicknesses were fabricated by cross accumulative roll bonding (CARB). Interface stability of V/Cu nano-multilayers with different layer thicknesses and their effects on thermal conductivity and helium irradiation have been explored. The microstructure analysis, tensile and hardness tests result show that V/Cu nano-multilayers maintain high mechanical properties and good thermal stability after annealing at 500 °C for 1 h. However, the strength drastically degrades after higher-temperature annealing because of microstructure instability, which is closely related to the aspect ratio of grains. Furthermore, spheroidization occurring in multilayer during the annealing process promotes efficient electron transportation and weakens electron scattering, which benefits the increase of thermal conductivity. The irradiation response of V/Cu nano-multilayers was explored by helium bombardment with a fluence of 1 × 1017 ions/cm2 at room temperature and 500 °C, respectively. Helium bubbles transform to gas cavities with increasing irradiated temperature, and different morphology of cavities at heterointerface, newly formed grain boundaries and triple junctions is attributed to the defect diffusion preference combined with thermal-induced interfaces migration.

RETRACTED: Investigating the solid-state diffusion at the interface of Ni/Ti laminated composite

The fabrication of Ni/Ti laminated composite via cross accumulative roll bonding (CARB) and subsequent annealing treatment has been studied. The relationships between annealing conditions and microstructure at interfaces of Ni/Ti have been investigated by SEM, XRD, and EDS analyses. The results show that the layers were well-bonded by the CARB process, and by increasing the temperature and time of annealing treatment, the interfacial layers grew as a result of the interdiffusion of Ni and Ti atoms. The main intermetallic phases were NiTi and NiTi 2 , both of which obeyed linear kinetics of growth. However, the calculated activation energy of NiTi was lower than that of NiTi 2 , indicating the comparable growth of NiTi. Further, based upon the results of tensile tests, the ultimate strength of samples decreased as the intermetallic layers grew; the detachment of layers and the intergranular fraction of intermetallic compounds were the main fracture mechanisms. • Ni/Ti laminated composite was produced by using the CARB process and post-annealing. • The following sequence of phases was detected: Ti/NiTi 2 /NiTi/Ni 3 Ti/Ni • The thickness of NiTi 2 and NiTi layers rose as the temperature and time of annealing treatment increased. • As the intermetallic layers grew, the values of ultimate tensile strength and elongation decreased and fluctuated, respectively.

Mechanical properties and strength prediction of Al/E-glass fiber composites fabricated by cross accumulative roll bonding process

In this work, Al/E-glass fiber composites were fabricated by the cross accumulative roll bonding (CARB) process, and their structure and mechanical behaviors were investigated. The structural characterization by X-ray diffraction and scanning electron microscopy indicates that the continuous fibers are fragmented during the CARB process, leading to the production of an ultrafine-grained short fibers reinforced composite at the final cycle. A combined model was used to predict the yield strength of the fabricated Al/E-glass fiber composites. Also, the yield strength of the samples was measured by tensile tests. The agreement of the calculated and measured yield strength showed the model used for the strength prediction is dependable. The investigation of the micro-hardness and wear properties of the composites depicted that by increasing the CARB cycles, despite the increase in micro-hardness, the wear resistance is decreased, which was attributed to the layered structure. • Long fibers were crushed during the CARB process and changed to short fibers. • The final product of the process was an ultrafine-grained short fibers composite. • The predicted yield strength was in agreement with the measured value. • The main wear mechanism of the composite samples was delamination.

Structural, mechanical and corrosion evaluations of Cu/Zn/Al multilayered composites subjected to CARB process

In this research, the structure, tensile, wear, fracture toughness, and corrosion characteristics of Cu/Zn/Al multilayered composites fabricated by cross accumulative roll bonding (CARB) were determined. X-ray diffraction and scanning electron microscopy were used for structural analyses. Results showed that the crystallite size of the Cu matrix is reduced to about 50 nm at the ninth cycle of CARB, while the plastic instability and shear bands appeared in the layers after the third cycle. The tensile strength of the composites increased up to the third CARB cycle and then decreased to the ninth CARB cycle gradually. Typically, the maximum strength of about 330 MPa and elongation of almost 31.5% were obtained at the third and first cycles, respectively. A similar trend was found for the fracture toughness of the samples, so that the maximum fracture toughness of about 31 MPa.m1/2 was obtained at the third cycle. It was also shown that the wear mechanism of the composite samples changes by increasing the cycles, a compromise of abrasion and delamination wear. The accommodation of Al and Zn layers toward the surface of the composites by increasing the CARB cycles was also recognized to be responsible for the decrease of the corrosion resistance determined by polarization experiments.

High strength, high electrical conductivity and thermally stable bulk Cu/Ag nanolayered composites prepared by cross accumulative roll bonding

Bulk Cu/Ag multilayered composites with controlled individual layer thickness (h) varying from several hundred micrometers down to 20 nm were fabricated via cross accumulative roll bonding (CARB). The well-defined, continuous Cu/Ag multilayer structure with flat, planar, and sharp interfaces was found to remain stable when the layer thickness was reduced from several hundred micrometers down to 20 nm. A preferential interface character of {110}Cu[111]//{110}Ag[111] was formed when the layer thickness was reduced to 20 nm. Specifically, high strength, high electrical conductivity and excellent thermal stability were obtained simultaneously in bulk Cu/Ag nanolayered composite with h = 20 nm. Ultimate tensile strength of 938.1 MPa was achieved, corresponding to 2.9 times higher than the rule-of-mixtures estimate based on the strength of the heavily deformed Cu and Ag samples with 95% rolling reduction. Furthermore, a high electrical conductivity higher than that of pure copper was obtained, while high hardness (3.74 GPa) was maintained up to an annealing temperature of 500 °C. Nevertheless, degradation of the mechanical hardness and nanolayered structure occurred once the temperature exceeded 500 °C. Two major mechanisms are responsible for driving the onset of the thermal instability in this CARB-processed Cu/Ag nanolayered composites, namely triple junction motion and Rayleigh instability mechanisms.

Study on thermal stability and irradiation response of copper/iron nano-multilayer composite fabricated by cross accumulative roll bonding

Nano-multilayer composites simultaneously exhibit high strength and good radiation resistance because of its huge density of interfaces. However, such outstanding behaviors are influenced by their thermal stability. In this study, we investigated the evolution of microstructure and hardness in Cu/Fe composites fabricated by cross accumulative roll bonding (CARB) with different individual layer thicknesses and annealing time. The results demonstrated that the composites with a layer thickness of 90 nm are more resistant to layer pinch-off and spheroidization, and maintain a relatively high strength after the long-time annealing at 400 °C. By contrast, the decreasing Cu/Fe interface density and severe grain spheroidization in the 30 nm sample lead to a significant drop in hardness. Furthermore, as for helium irradiation response in the 90 nm Cu/Fe composite at 500 °C, some columnar voids with a large aspect ratio appear at Cu/Fe interfaces, demonstrating that void elongation in the normal direction of the interface requires to satisfy both kinetic (along vacancy flux) and thermodynamic (along {111} plane) factors. In addition, the obviously increasing bubble size mainly contributes to the hardening in Cu/Fe multilayers after high-temperature irradiation.

Influence of Intermediate Heating in Cross Accumulative Roll-Bonding Process on Planar Isotropy of the Mechanical Properties of Commercial Purity Aluminium Sheet

In this study, the cross accumulative roll-bonding (CARB) process, as an improved technique of the conventional accumulative roll-bonding (ARB), was conducted on the AA1050 sheet up to 10 passes in two processing modes. The specimens were either preheated before the rolling step of CARB passes and promptly roll bonded (warm CARB) or were processed at room temperature (cold CARB). The microstructure of samples was characterized using a scanning electron microscope. The effect of intermediate heat treatment on the planar homogeneity of the mechanical properties in the CARB (and even ARB) deformed sheets has not been examined yet. Hence, the present research focuses on the comparison of the planar isotropy of tensile properties between warm and cold CARB products. Also, the uniformity of microhardness distribution throughout the thickness of samples was evaluated. The warm CARB presented higher elongation, lower tensile strength and microhardness with more uniformity of the microhardness distribution, and also premier planar isotropy of the mechanical properties than the cold CARB.

Graded microstructure and texture in ultrafine grained multi-layered immiscible bimetallic system

In this investigation we report the formation of a graded microstructure in copper/tantalum ultrafine grained (UFG) multi-layered composite fabricated by cross accumulative roll bonding (CARB) process at high temperatures. The microstructure, micro-texture and bulk texture evolution in the copper/tantalum composite was established. A gradient microstructure develops along the thickness of the specimen during the CARB process. The fragmentation of tantalum in between copper layers and the grain refinement with evolving passes has been explained. The deformed copper layers show rotated cube texture and deformed tantalum layers show cube texture with γ-fibre. The overall texture of copper/tantalum composite weakens after the process of ARB; copper undergoing texture randomization post annealing. The crucial role of interfaces on the evolution of texture is demonstrated. The microstructural gradient in the specimen possess equiaxed, lamellar as well as large deformed grains with tantalum's grain size being in the scale of 200 nm. The correlation of microstructural gradient with orientation relationship (OR) between copper and tantalum layers was studied, confirming higher misorientation in OR at regions under high strain. Dynamic recrystallization taking place at the copper/tantalum interface has been elaborated with the aid of microtexture analysis.

Structure, wear and corrosion characterizations of Al/20wt.% Zn multilayered composites fabricated by cross-accumulative roll bonding

In this study, Al/20 wt.% Zn laminated composites are produced by the cross-accumulative roll bonding (CARB) process. The microstructural, mechanical and corrosion characteristics of the composites are investigated at different passes of the CARB process. Using scanning electron microscopy, it is observed that during the CARB process, the Zn layers are necked, ruptured and gradually distributed in the Al matrix. Tensile testing results reveal that the incremental trend of strength stops unexpectedly at the sixth pass and then continues again at the higher passes, reaching 275 MPa at the eighth pass. The wear resistance of the samples increases up to the fourth pass, whereas it decreases gradually at the higher passes contrary to expectations. A mixed mode of abrasion, adhesion and delamination mechanisms is found to control the wear damage of the samples. The corrosion current density of the samples fabricated at the first pass is 3 times higher than the eighth pass, indicating the improvement of the corrosion resistance. Also, Nyquist plots show a single capacitance loop attributed to the formation of a passive film.

Graded Microstructure and Texture in Ultrafine Grained Multi-Layered Immiscible Bimetallic System

In this investigation we report the formation of a graded microstructure in copper/tantalum ultrafine grained (UFG) multi-layered composite fabricated by cross accumulative roll bonding (CARB) process at high temperatures. The gradient microstructure develops as a consequence of the strain gradient present along the thickness of the specimen during the CARB process. The correlation of strain gradient with the microstructure, micro-texture and bulk texture in copper/tantalum composite was established. The fragmentation of tantalum in between copper layers and the grain refinement with evolving passes has been explained. The deformed copper layers show rotated cube texture and deformed tantalum layers show cube texture with γ- fibre. The overall texture of copper/tantalum composite weakens after the process of ARB; copper undergoing texture randomization. The crucial role of interfaces on the evolution of texture is demonstrated. The effect of strain on orientation relationship (OR) between copper and tantalum layers was studied, confirming higher misorientation in OR at regions under high strain. Dynamic recrystallization taking place at the copper/tantalum interface has been elaborated with the aid of microtexture analysis.

Effects of annealing temperature and layer thickness on hardening behavior in cross accumulative roll bonded Cu/Fe nanolamellar composite

Bulk Cu/Fe nanolamellar composites with different layer thickness were fabricated by cross accumulative roll bonding (CARB) technique. Here, annealing induced hardening and strengthening behaviors were observed in these composites as annealing temperature rises up to 400 °C. Especially, the increasing rate of strength and hardness are more remarkable in those with thinner layers. Then, mechanical properties gradually degrade after annealing at higher temperatures due to the destruction of layer structure. Detailed microstructural characterizations demonstrate that miraculous abnormal hardening of Cu/Fe nanolamellar composites induced by annealing is attributed not only to the density reduction of mobile dislocation inside heterogenic layers but also to the relaxation of non-equilibrium interphase boundaries. Furthermore, this phenomenon is closely correlated with the individual layer thickness, which is revealed by the diffusion effect of excess defects in the interfacial transition zones.

Comparative Study of the Planar Uniformity of the Mechanical Properties of the AA1050 Strips Processed by Conventional and Cross Accumulative Roll-Bonding Techniques

In this research, a modified method of the conventional accumulative roll-bonding (ARB) process, named cross accumulative roll-bonding (CARB), was applied on an AA1050 strip for up to 13 cycles. The planar uniformity of the mechanical properties in the products of ARB and CARB processes has not been investigated yet. This article aims to compare the planar inhomogeneity of the tensile properties in different directions of the rolling plane of the ARB- and CARB-processed specimens. For this purpose, uniaxial tensile tests were performed in the rolling, transverse, and diagonal directions of the products. Furthermore, Vickers microhardness was used to investigate the hardness distribution throughout the thickness of specimens. The results revealed that the CARB process exhibited higher tensile strength, elongation, and hardness with more homogeneous distribution of the hardness and particularly better planar uniformity of the tensile properties compared with the conventional ARB process.

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

Mg-5Li-1Al alloy was processed by cross accumulative roll bonding (CARB). The processed Mg-5Li-1Al sheet possesses ultra-fine grains, and its strength increases both in the rolling direction (RD) and transverse direction (TD) with the elongation remaining 16˜18%. The proper CARB processing is helpful to improve the isotropy of mechanical properties of Mg-5Li-1Al sheet. At the same time, the CARB process has a beneficial effect on improving the plasticity of Mg-5Li-1Al sheet. With the change of the direction between the CARB passes, the basal texture of Mg-5Li-1Al sheet is weakened, and the non-basal texture is strengthened. Both prismatic slip and pyramidal slip are initiated. The dominant deformation mechanism changes from twin deformation to slip deformation, and finally shear deformation. The grain refinement mechanism changes from twin dynamic recrystallization to continuous dynamic recrystallization, and finally rotational dynamic recrystallization.

Aluminum-matrix composites reinforced with E-glass fibers by cross accumulative roll bonding process

In this research, the structure and mechanical properties of 1050 aluminum strips reinforced with E-glass fibers, processed by the cross accumulative roll bonding (CARB) process, were investigated from microscopic, hardness, tensile and peeling viewpoints. The results indicated that the incorporation of the glass fibers in the Al matrix increases strength and micro-hardness but decreases elongation. In addition, it was realized that some of these fibers are broken and changed to short fibers during the CARB process. The presence of the glass fibers strongly also reduces the bond efficiency of the Al strips, typically from 50% to 5%. To compensate this deleterious effect, it was found that at least 25% should be increased to the normal thickness reduction used in CRAB.