ARB Cycles Research Articles

Through Thickness Microstructural and Texture Inhomogeneity Within Al Layers in ARB-Produced Al-Al(Sc) Layered Composite Sheets

Alternatively layered composite sheets of commercially pure (99.8 pct purity) aluminum and an Al-0.3wtpctSc alloy (either in the supersaturated solid solution or age-hardened conditions) were generated through accumulative roll bonding for up to 5 cycles. The transverse sections of the sheets were examined to investigate the microstructure and texture inhomogeneities developed during the rolling process. Electron backscatter diffraction and transmission electron microscopy was used for this investigation. It was found that an inhomogeneous microstructure and texture was developed through the aluminum layers of the sheet thickness. The nature of inhomogeneities changes as the ARB bonding progresses to higher cycles. Microstructural inhomogeneities remain prominent in the first ARB cycle and diminish during the subsequent cycles. Texture inhomogeneities appear in different forms as rolling progresses. High frictional shear forces in the surface and in-plane shear forces across bonding interfaces derive these inhomogeneities.

Microstructure and Mechanical Properties of Nanostructured 1050/6061 Aluminum Alloy Fabricated by Four-Layer Stack Accumulative Roll-Bonding.

An ultrafine grained AA1050/AA6061 Al alloy sheet was successfully fabricated by four-layer stack ARB process. The ARB of AA1050 and AA6061 alloy sheets was performed up to 3 cycles without a lubricant at ambient temperature. The sample fabricated by the ARB was a multi-layer aluminum alloy sheet in which AA1050 and AA6061 layers are alternately stacked. The layer thickness of the each alloy became thinner and elongated to the rolling direction with increasing the number of ARB cycles. The tensile strength increased with the ARB, it reached about 347 MPa which is almost 2.4 times that of the starting material. The grain size decreased with increasing of the number of ARB cycles, became about 190 nm in thickness after 3 cycles. The variation of mechanical properties with the ARB was similar to those of the other ARB processed materials. However, the texture development was different from those of the conventional ARB processed materials.

Evaluation of Mechanical Properties and Structure of 1100-Al Reinforced with Zro2 Nano-particles via Accumulatively Roll-bonded

In this study, aluminium metal composites reinforced with Zirconium dioxide (ZrO2) nano-particles in different of volume percentage are manufactured through accumulative roll bonding. The results indicate that with the application of 10 ARB cycles and the composite microstructure shows excellent ZrO2 particle distribution in the Al matrices. The X-ray diffraction results also showed that nanostructured Al/ZrO2 Nanocomposite with the average crystallite size of 48.6nm was successfully achieved by employing 10 cycles of ARB process. According to the results of this study, the tensile, hardness, and elongation properties of the Al/ZrO2 composite are determined for 0.50, 0.75 and 1 vol.% ZrO2.

Investigation of microstructure and mechanical properties of Cu/ZnO nano composite produced by ARB process

In this study, ARB process was used to produce Cu/Nano ZnO composite and samples were subjected up to six ARB cycles. Microstructural and mechanical properties of the composite within different ARB cycles were investigated by scanning electron microscopy (SEM) and tensile and micro hardness tests. The results showed that increasing the number of cycles, not only helped the distribution of reinforcing Nano-reinforcement in the matrix, but also improved the initial bonding strength, so that at final cycles, structural integration was achieved. Mechanical experiments also showed that increasing the number of ARB cycles, increased yield and ultimate strengths as well as micro hardness. However, elongation decreased up to second cycle and then increased by later final cycles. SEM studies of the fracture surfaces after the tensile test showed that the fracture mechanism of the composite was shear ductile rupture.

Effects of TC4 foil on the microstructures and mechanical properties of accumulatively roll-bonded aluminium-based metal matrix composites

In the present study, Ti–6Al–4V alloy (TC4) foils were initially used as raw materials to produce aluminum-based metal matrix composites via the warm accumulative roll-bonding process. A composite with homogeneously distributed TC4 fragments in Al matrix was produced after 12 ARB cycles were performed. Microstructure analyses revealed that the thickness and length of the TC4 phase and the Al grain size in the Al/TC4 composites were refined by increasing the number of ARB cycles. Compared with the pure metal fragments in Al/pure metal systems, the TC4 fragments in Al/TC4 were thick and long because of the low plasticity–high strength of TC4 phase. The tensile properties of the Al/TC4 composites were also investigated. Results showed that the tensile strength and elongation increased with the number of ARB cycles and reached the maximum values of 147MPa and 4.2% after 12 cycles were performed, respectively. Compared with the ARB monolithic, 1060-Al, Al/TC4 composites exhibited higher strength but lower elongation after 12 ARB cycles were conducted.

The effect of alumina content on the mechanical properties of hybrid composites fabricated by ARB process

In the present work, the effect of particle content on the mechanical properties of hybrid composites fabricated by anodizing and accumulative roll bonding processes was investigated. The ARB process was used for the fabrication of the hybrid composite, including different contents of alumina particles. Microstructural observations and fractography were performed by scanning electron microscopy (SEM). Also, the mechanical properties were investigated by tensile and microhardness tests. It was realized that when the number of ARB cycles was increased, uniformity of particles distribution was improved in the aluminum matrix. Also, with increasing the number of cycles, the tensile strength of hybrid composites was increased too. In addition, with increasing the alumina content in the aluminum matrix, the tensile strength and elongation of hybrid composites were increased and decreased, respectively. The ARB-processed hybrid composites exhibited a higher hardness value than that of the annealed sample. Moreover, with increasing the alumina content in the aluminum matrix, the hardness of hybrid composites was increased. It was also found that with increasing the number of cycles, the bond strength of all interfaces was improved and the unbonded regions of the interface were decreased. The hybrid composites after the first and second cycles exhibited a typical ductile fracture showing deep equiaxed dimples, whereas the fracture mode after the fourth cycle was a combination of ductile and shear ductile fracture.

Influence of cross-rolling on the mechanical properties of an accumulative roll bonded aluminum alloy AA6014

Sheets of aluminum AA6014 (AlMgSi) were successfully accumulative roll bonded from T4 condition up to eight cycles. Using the conventional ARB route, processing was on the one hand performed at room temperature. On the other hand, sheets were pre-heated in a furnace for 2.5min at 210°C prior to each rolling step. Besides the conventional ARB route an ARB cross-rolling route, where the rolling direction is rotated around 90° after each cycle, was used at room temperature. For all three processing conditions an ultrafine-grained microstructure was obtained. Due to a change in strain path, the ultimate tensile strength and the yield strength of the cross-rolled AA6014 exceed those of the samples processed by conventional ARB. However, a strong decrease in terms of elongation to failure is visible after 6–8 cycles of ARB compared to the pre-heated ARB sheets. Fracture analysis reveals necking of individual layers for the samples processed at room temperature. Therefore, after 7 cycles of cross-rolling at RT, one last cross-rolling step at elevated temperature was performed in order to improve bonding quality. This leads to a high strength of about 475MPa and a satisfactory elongation to failure of about 10%.

Mechanical properties of aluminium laminates produced by accumulative roll bonding

Laminates of high and commercial purity aluminium layers were processed by accumulative roll bonding performed up to ten cycles. The mechanical properties were measured by tensile testing. Both yield strength and ultimate tensile strength increase with higher number of cycles. The fracture strain is decreased through the first ARB cycle, but increases during further processing to reach a maximum after the sixth cycle. It is found that the development of the microstructure, especially in the high purity layers, strongly influences the mechanical properties.

Microstructure and Texture of a Nano-Grained Complex Al Alloy Fabricated by Accumulative Roll-Bonding of Dissimilar Al Alloys

An ultrafine grain (UFG) complex lamella aluminum alloy sheet was successfully fabricated by ARB process using AA1050 and AA6061. The lamella thickness of the alloy became thinner and elongated to the rolling direction with increasing the number of ARB cycles. By TEM observation, it is revealed that the aspect ratio of UFGs formed by ARB became smaller with increasing the number of ARB cycles. In addition, the effect of ARB process on the development of deformation texture at the quarter thickness of ARB-processed sheets was clarified. ARB process leaded to the formation of the rolling texture with shear texture and weak cube orientation. The subdivision of the grains to the rolling direction began to occur after 3 cycles of the ARB, resulting in formation of ultrafine grains with small aspect ratio. After 5 cycles, the ultrafine grained structure with the average grain diameter of 560 nm develops in almost whole regions of the sample.

Texture Evolution in Al–0.2 mass%Sc Alloy during ARB Process and Subsequent Annealing

Evolution of textures in the solution treated and aged Al­0.2Sc alloy heavily deformed by ARB process and subsequently annealed was investigated using pole figure and orientation distribution functions (ODF) that were determined by electron backscatter diffraction (EBSD) technique. Three kinds of starting materials were prepared before the ARB process: solution treated (ST) material, 300°C-aged material including fine Al3Sc precipitates, and 400°C-aged material having coarse Al3Sc precipitates. The results of deformation texture indicated that at early stage of ARB S {123} h634i orientation component developed and it changed to Copper {112} h111i and Taylor {4411} h11118i components at later ARB cycles in both ST-ARB and Aged-ARB specimens. However, in the Aged-ARB specimens after 5-cycle ARB process, Copper {112} h111i component decreased and Taylor {4411} h11118i component did not developed. Cube {100} h001i component strongly developed in the 400°C Aged-ARB specimen by annealing at high temperature, whereas Cube component did not develop in the ST-ARB and 300°C Aged-ARB specimen. Such a difference was understood as the effect of Al3Sc precipitates. [doi:10.2320/matertrans.MA201223]

Production of high strength Al–Al 2O 3 composite by accumulative roll bonding

Recently accumulative roll bonding has been used as a novel method to produce particle reinforced metal matrix composites. In this study, aluminum matrix composite reinforced by submicron particulate alumina was successfully produced and the effects of number of ARB cycles and the amount of alumina content on the microstructure and mechanical properties of composites were investigated. According to the results of tensile tests, it is shown that the yield and tensile strengths of the composite are increased with the number of ARB cycles. Scanning electron microscopy (SEM) reveals that particles have a random and uniform distribution in the matrix by the ARB cycles and a strong mechanical bonding takes place at the interface of particle-matrix. It is also found that the tensile strength of the composite, as a function of alumina content, has a maximum value at 2 vol.%, which is 5.1 times higher than that of the annealed aluminum.

Microstructure and Tensile Properties of Ultrafine Grained Pure Al Sheets Produced by Accumulative Roll Bonding

Usually the heat treatment in the cyclic ARB passes is indispensable to reduce work-hardening effects and improve interface bonding quality. The possibility of accelerating grain refinement of aluminum sheets with a dimension of 300 mm×50 mm×1 mm is investigated during the ARB process at room temperature, in which the samples are rotated by 180 degree around normal plane axis perpendicular to the rolling plane between the adjacent cycles. By means of optical microscopy and transmission electron microscopy, it shows that the bonding interfaces can not obviously observed after five cycles, and grains are refined to be ~0.5 μm. Tensile tests show the ARB samples exhibit strain hardening behavior after yielding without a sudden fracture even up to seven cycles of ARB. The softening behavior and enhanced ductility was explained by dynamic recovery, the recrystallization process and even abnormal large grains.

Mechanical and corrosion resistance of a new nanostructured Ti–Zr–Ta–Nb alloy

In this work, a multi-elementary Ti–10Zr–5Nb–5Ta alloy, with non-toxic alloying elements, was used to develop an accumulative roll bonding, ARB-type procedure in order to improve its structural and mechanical properties. The alloy was obtained by cold crucible semi-levitation melting technique and then was ARB deformed following a special route. After three ARB cycles, the total deformation degree per layer is about 86%; the calculated medium layer thickness is about 13 μm. The ARB processed alloy has a low Young’s modulus of 46 GPa, a value very close to the value of the natural cortical bone (about 20 GPa). Data concerning ultimate tensile strength obtained for ARB processed alloy is rather high, suitable to be used as a material for bone substitute. Hardness of the ARB processed alloy is higher than that of the as-cast alloy, ensuring a better behaviour as a implant material. The tensile curve for the as-cast alloy shows an elastoplastic behaviour with a quite linear elastic behaviour and the tensile curve for the ARB processed alloy is quite similar with a strain-hardening elastoplastic body. Corrosion behaviour of the studied alloy revealed the improvement of the main electrochemical parameters, as a result of the positive influence of ARB processing. Lower corrosion and ion release rates for the ARB processed alloy than for the as-cast alloy, due to the favourable effect of ARB thermo-mechanical processing were obtained.

Processing of Ultrafine Grained Cu-30%Zn Alloy through Severe Plastic Deformation Using Accumulative Roll Bonding

In the present research, the microstructural features of ultrafine grained Cu-30 Zn alloy via ARB at room temperature were investigated by X-ray diffraction peak profile analysis. The character of dislocations was determined by analyzing the dislocation contrast factors. The average contrast factors for the different reflections obtained by determination of the type of dislocations and Burgers vectors in crystals. Also, using the modified Williamson–Hall and Warren–Averbach procedure size parameters, the effective outer cut-off radius and density of dislocations were determined. Assuming that the grain size distribution is log-normal, the median and the variance of the size distribution of sub grains were obtained. It was found that the crystallite size is reduced substantially, while the dislocation density increases up to 2 cycles of ARB. After 2nd cycle, dislocation density decreases. This is attributed to the occurrence of dynamic restoration process which takes place during next ARB cycles.

Microstructure and mechanical properties of accumulative roll bonded aluminium alloy AA5754

The aluminium alloy AA5754 is used for many technical applications. In this work, the accumulative roll bonding process is applied to this alloy in order to investigate the potential of an ultrafine-grained structure on the mechanical properties of this Al-Mg alloy. Sheets from AA5754 (AlMg3) were successfully processed by accumulative roll bonding in order to obtain an ultrafine-grained microstructure. The ARB process was performed at 230 °C or 250 °C up to 7 or 8 cycles respectively. Thus the grain size decreased from 10 μm (initial state) to approximately 80 nm (ultrafine-grained state, normal direction). The microstructural evolution and the mechanical properties have been investigated by means of scanning electron microscopy, hardness measurements and tensile testing. After one ARB cycle the samples showed an increase in hardness by a factor of almost 2 in comparison to the as-received material. Further processing causes a linear increase of hardness with each additional cycle. Yield strength and tensile strength of the roll bonded specimens are highly increased in comparison to the as-received samples whereas the ductility declined. A considerable increase in ductility is obtained by heat treatment of the ARB specimens at 250 °C, but on the expense of a moderate decreased strength. The deformation behaviour is also influenced by the ultrafine-grained structure. The occurrence of the Portevin-Le Chatelier effect is manifested by serrated stress-strain curves. The amplitude of serrations increases with increasing number of ARB cycles but can be reduced by the appliance of a higher strain rate. Lüders strain only occurs at the as-received, i.e. not strained, samples.

Nanomechanical behaviour of Al-Ti layered composites produced by accumulative roll bonding

In this study Ti-foils were roll bonded together with commercially pure aluminium AA1050. The laminates were produced by using two 1 mm thick AA1050 sheets at the outer side of the stack combined with 100 μm thick Ti-foils as an intermediate layer for each accumulative roll bonding process. The samples were rolled up to 4 ARB cycles. Subsequently the sheets were post-process heat treated at 180°C, 400°C or 600°C, respectively, for 24 hours. The local mechanical behaviour of the Al/Ti intermetallic interfaces have been investigated using nanoindentation experiments. A strong dependence between annealing-temperature, – time and deformation grade is detected. While a heat treatment at 180°C only leads to a weak bonding between Al and Ti with a preservation of the UFG structure, temperatures up to 600°C are causing a complete recrystallisation of the microstructure and formation of diffusion layers with different Al and Ti concentrations.

Fabrication of Ultrafine Grained Copper Alloy by 3-Layers Accumulative Roll-Bonding Process

The 3-layers accumulative roll bonding process (ARB) has been attempted to increase the strength of copper alloy (Cu-0.02wt.%P) by refining grain size. The 3-layers accumulative roll bonding was conducted up to 7 cycles at room temperature without lubrication. Microstructural evolution of the copper alloy with the number of the 3-layers ARB cycles was investigated by optical microscopy (OM), transmission electron microscopy (TEM), and electron back scatter diffraction (EBSD). The average grain size has been refined from 20 μm before ARB to 170 nm after 7 cycles of 3-layers ARB. More than 70% of ultrafine grains formed by 3-layers ARB were composed of high angle grain boundaries. The average misorientation angle of ultrafine grains was 30.7 degrees in the center of the specimen. Tensile strength after 7 cycles of 3-layers ARB was 605 MPa, which is about 3.2 times higher than the initial value.

Evolution of Nano-Grains in High Purity Copper by Accumulative Roll-Bonding Process

The evolution of nano-grains in oxygen free copper with accumulative roll-bonding is investigated by TEM and EBSD analysis. The ultrafine grains developed in the sample after 8-cycle ARB. It was found that the mean spacing of grain boundaries, which was 63 microm in initial material, reduced to 5.5 microm after 1 cycle, then surprisingly 450 nm after 3 cycles. In addition, the fraction of high-angle boundaries in the sample after 1-cycle ARB was 0.32, but it after 3-cycle ARB was surprisingly more than 0.6. Texture development of the ARB processed samples is different depending on the number of ARB cycles.

Manufacturing of high-strength aluminum/alumina composite by accumulative roll bonding

The ARB process used as a technique in this study provides an effective alternative method for manufacturing high-strength aluminum/alumina composites. The microstructural evolution and mechanical properties of the aluminum/15 vol.% alumina composite are reported. The composite shows an excellent alumina particle distribution in the matrix. It is found that by increasing the number of ARB cycles, not only does elongation increase in the composites produced but also the tensile strength of the Al/15 vol.% Al 2O 3 composite improves by 4 times compared to that of the annealed aluminum used as the original raw material. Fracture surfaces after tensile tests are observed by scanning electron microscopy (SEM) to investigate the failure mode. Observations reveal that the failure mode in both ARB-processed composites and monolithic aluminum is of the shear ductile rupture type.

Microstructure and tensile properties of Al–Mn alloy processed by accumulative roll bonding

Microstructure and tensile properties of ultrafine grained Al–Mn alloy by ARB at room temperature were investigated. With the cycles of ARB, the average grain size becomes smaller, and the pancake shaped ultrafine grains develop to be about 250 nm after five cycles. Meanwhile, the MnAl 6 phase in the shape of spherical particle is refined and uniformly distribute in the matrix. A fairly uniform microstructure would be facilitated by a multi-parabolic profile of shear strain distribution across the thickness of sheet. In the present ARB process, there exist two types of changes in deformation mode. One is changed from shear deformation (in the surface regions) to plain strain rolling (in the center). The other is that strain path is reversible due to a change of rolling direction in alternate cycles. Therefore, the process of grain refinement can be accelerated than the conventional ARB. The tensile tests show Al–Mn alloy exhibits strain hardening behavior after yielding without a sudden fracture even up to five cycles of ARB. The more the cycles of ARB, the smaller the decrease of work-hardening rate of Al–Mn specimens. The enhanced ductility was explained by dynamic recovery, the formation of ultrafine MnAl 6 phase, work-hardening and strain rate sensitivity.