Accumulative Roll Bonding Process Research Articles

Strain hardening and softening in ultrafine grained Al fabricated by ARB process

Deformation behavior of a commercial purity aluminium (99% purity) highly deformed by the accumulative roll-bonding (ARB) process was investigated by analyzing the change in the specimen shape during tensile test precisely. True stress obtained by the specimen shape analysis of the conventionally coarse grained material was found to increase continuously even after necking, which indicated that the necking region was work-hardened. On the other hand, true stress of the ARB-processed Al which showed lamellar boundary structure having the mean lamellar spacing of 220 nm decreased after necking, which was quite different from the result of the coarse grained material. This result suggests that the necking region is not hardened but softened by deformation. The softening is considered to be caused by dynamic recovery at grain boundaries.

Texture development of ARB processed Mg/Al multilayers

Our work deals with accumulative roll bonding (ARB) of pure Mg sheet (0.9mm thickness) and of Al5052 sheet (0.5mm). A stacking of Al-Mg-Al was firstly rolled to 50% reduction at 400°C and secondly ARB has been processed up to 3 cycles. In such multilayers as well as highly mixed composites of two-phased system texture development, phase reactions and strain accumulation are of basic interest, which needs a combination of different experimental methods for characterization. The present paper deals with the global texture evolution measured by thermal neutrons to average always over the whole sample thickness, SEM and optical microscopy indicates the macroscopic development of Mg and Al layers. The initial materials show typical and strong basal plane texture of hexagonal Mg (17.9mrd) and a recrystallization texture of cubic Al (8.5mrd). Co-deformation of Al/Mg/Al leads to strong decrease of both textures, whereas Mg has always a much stronger texture than Al5052. ARB processing produces only weak Al-textures. After sandwich-rolling and 1 cycle ARB rotated cube is observed in Al5052, which does not exist after 2 and 3 cycles of ARB.

Analysis of deformation behaviors of ultrafine grained Cu-30%Zn with bimodal grain-size distribution

Ultrafine grained (UFG) metals have remarkably high strength in comparison with that of coarse grained metals. However, the UFG metals often exhibit low tensile ductility. It has been reported that the UFG metals having bimodal grain-size distributions consisting of coarse grains and fine grains perform large elongation keeping high strength. However, the exact deformation mechanism of the bimodal UFG metals has not yet been clarified. Deformation behaviors of a bimodal UFG metal were studied in the present paper. A sheet of Cu-30%Zn was highly deformed by accumulative roll-bonding (ARB) process and then annealed. The annealed specimen showed a fully-recrystallized UFG structure with a bimodal grain size distribution. To clarify deformation behaviors of the bimodal metal, an identical region was observed by the electron backscattered diffraction (EBSD) method at various tensile strains. The grain average misorientation (GAM) increased with increasing the tensile strain. The increase in GAM of the coarse grains was larger than that of the fine grains, suggesting the difference in local deformation and strain-hardening behaviors between different grain sizes. The enhanced uniform elongation of the bimodal UFG specimen was considered to be associated with the difference in strain-hardening between the coarse grains and fine grains.

Susceptibility to Hydrogen Embrittlement of IF Steel with Ultrafine-Grained Structure Produced by Accumulative Roll-Bonding Process

We have investigated the susceptibility to hydrogen embrittlement of interstitial-free (IF) steel with ultrafine-grained microstructure produced by accumulative roll-bonding (ARB) process. The ARB process was conducted to as-received IF steel at 773 K, and repeated to five cycles. The as-received and the ARBed IF steels were cut into tensile specimens, and then hydrogen was electrochemically charged to the specimens in a sulfuric acid solution of pH 2.5 at a cathodic current density of 50 A m-2 for several charging times. Immediately after the hydrogen-charging process, tensile test was conducted at ambient temperature and an initial strain rate of 3.3 x 10-4 s-1. Besides, state and amount of hydrogen absorbed in the specimen were determined with a thermal desorption gas spectroscopy (TDS) at a heating rate of 5.6 x 10-2 K s-1. As a result, almost no hydrogen was absorbed in the as-received IF steel charged for a long time of ca. 300 ks, and a fracture strain of the steel was independent of the charging time. On the other hand, amount of hydrogen in the 5-cycle ARBed steel increased with an increase in the charging time, and the fracture strain decreased with an increase in the charging time, indicating that the ARBed steel exhibited susceptibility to hydrogen embrittlement.

Fatigue Fracture Behavior of ARB Processed Aluminum

Fatigue crack propagation behaviors of ultrafine grained (UFG) Al sheets fabricated by the accumulative roll bonding (ARB) process were investigated. The ARB process was carried out up to 6 cycles (equivalent strain, eq.=4.8). The ARB processed sheet had lamellar boundary structure elongated to rolling direction of the sheet. The mean spacing of the boundaries was 182 nm. The tensile strength of the starting Al sheet increased after the 6-cycle of the ARB. Fatigue crack growth tests were performed to clarify the crack growth rate and threshold stress intensity factor range for crack growth (Kth). The fatigue crack profile in the ARB processed sheet differs from that in the starting Al sheet. The Kth of the ARB processed sheet was smaller than that of the starting sheet. The Kth of Al would decreased with decreasing the crack closure phenomena after the 6-cycle of the ARB. The fatigue crack growth rate test shows that the critical load for starting to propagate the fatigue crack and the fatigue crack growth rate decreased by ultrafine grain refinement.

Hardness measurements of accumulative roll-bonded Mo foils

The hardness of accumulative roll bonding (ARB)-processed multilayers has been measured in the past with microindentation studies. In some cases the lateral indent size of microindenters, however, is too large. For example, if multilayers are ARB-processed that consist of arrays of different elemental foils the hardness ratio of the layers has been reported as a key factor for the development of diffuse necking. To predict diffuse necking during ARB processing, flow stress data are usually taken from tensile tests. Flow stresses can be estimated of individual layers based on hardness measurements. In this work results are compared between hardness measurements on ARB-processed Mo multilayers with micro- and nanoindentation. Two sets of Mo multilayers were examined, one with as-received Mo foils and a second set with annealed Mo foils as starting material. The microhardness measurements show an increase in hardness with the first two passes before the hardness reaches a near plateau for the annealed Mo foils. The as-received foils that appear to be cold-worked yield a constant hardness for the first five passes that approaches the hardness of the annealed samples after four passes. The nanoindentation measurements were conducted at the center of Mo grains. If the indentation size effect (ISE) is taken into account the nanoindentation-based hardness measurements of the annealed Mo foil multilayers agree with the microhardness measurements. For the multilayer comprised of as-received Mo foils, agreement is obtained with the microhardness measurements even without taking into account an ISE. These observations are discussed with respect to the changes in microstructural length scales during ARB processing and the indent sizes. A main conclusion is that nanoindentation measurements yield reliable hardness data if the ISE is considered.

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.

Cu/Zr nanoscaled multi-stacks fabricated by accumulative roll bonding

In this paper, six pure Cu (99.96 mass%) and five pure Zr (99.8 mass%) sheets with overall composition of Cu 62Zr 38 (at%) were alternatively stacked and severely deformed up to equivalent strain ( ɛ) of 14.4 by accumulative roll bonding (ARB) technique at ambient temperature. During the ARB process, every individual Cu and Zr sheet in the multi-stacked materials decreases greatly in thickness with the increase of ɛ. Finally, nanolamellar structure with single layer thickness of about 20 nm can be obtained in the ARB processed Cu/Zr multi-stacks. Tensile tests were used to evaluate the mechanical properties of the ARB processed Cu/Zr multi-stacks related to the variations of ɛ. It reveals that the tensile strength increases greatly from 570 MPa at ɛ = 1.6 to 1210 MPa at ɛ = 14.4. However, the plastic elongation first increases from 8% at ɛ = 1.6 to 14% at ɛ = 9.6 and then decrease to 6% at ɛ = 14.4. The equivalent strain dominated microstructural evolution and deformation behavior of the ARB fabricated multi-stacks were put forward and discussed.

Microstructure and mechanical properties of the Mg/Al laminated composite fabricated by accumulative roll bonding (ARB)

The Mg/Al laminated composite was fabricated by the accumulative roll bonding (ARB) using the pure magnesium and Al5052 alloy at 400 °C. Tensile properties along rolling direction and the transverse direction and the microhardness were evaluated at the ambient temperature. The tensile strength of the laminated Mg/Al composite along both directions increased gradually till two ARB cycles, but then decreased after the third ARB cycles. Optical microscopy and scanning electron microscopy (SEM) were utilized to reveal the microstructure evolution and the failure mechanism. Grain refinement of Mg layers was not obvious during the ARB process due to the high temperature and interval reheating. The obvious crack at the coarse intermetallic compounds and rupture of the Al layer after the third cycle led to the premature failure of the sample along the rolling direction during the tensile test.

Textural evolution of nano-grained 70/30 brass produced by accumulative roll-bonding

The accumulative roll-bonding (ARB) process was carried out on the 70/30 brass alloy sheet up to six cycles to obtain nano-grains. Texture evolution during ARB of 70/30 brass was investigated using X-ray diffraction (XRD). The results indicate that characteristic features of the rolling texture in the 70/30 brass become discernible in the first cycle with the appearance of the twinning component {2 5 5}〈5 1 1〉 (TC), Y {1 1 2}〈1 1 1〉, Goss {1 1 0}〈0 0 1〉, and Brass (0 1 1)〈2 1 1〉 components. During the first cycle, deformation twinning plays a major role in texture evolution, whereas after two cycles, twinning activity diminishes and shear bands dominantly lead to the formation of Goss and Brass, which remain as the major components in higher cycles. With increasing number of cycles, the overall texture intensity does not increase monotonously. After the second cycle, a drop occurs in texture intensity related to the shear strain incurred in the sheets while, after the third cycle, the overall intensity reaches its maximum value. After six cycles, texture intensity reduces slightly, which can be explained by nano-grain formation.

Microstructure, Properties and Annealing Behavior of an ARB-Processed Al20%Sn Alloy

Severe plastic deformation processes are used to refine grain structure by means of very high deformations. Equivalent Von-Mises strains in the range of 5.06 to 11.57 were obtained using the accumulative roll-bonding (ARB) process. The effect of the initial microstructure is analyzed. Microstructure, microhardness and tensile strength of the alloy, both starting with previously cold-rolled material and after a 30 minute, 300 °C heat treatment, are compared. The effect of a heat treatment after 5 steps of ARB ( = 8.11) is also presented. Results show that even though both the microhardness and tensile strength go up with increasing deformation, they are not related to each other by a factor of 3. The highest values of these parameters depend more on the initial microstructure than on the total deformation. A better distribution of the second phase and an increase in solid solubility are also observed after ARB.

Fabrication of nanostructure Al/SiCP composite by accumulative roll-bonding (ARB) process

Abstract In the present study, a new manufacturing process for Al–SiC P composites was developed by using bulk aluminum sheets and micron sized SiC particles as starting materials. Nanostructured Al–SiC P composites with average grain size of 180 nm were successfully produced in the form of sheets, through accumulative roll bonding (ARB), at room temperature. To evaluate microstructure of the produced composites, scanning electron microscope (SEM) and transmission electron microscope (TEM) were applied. The microstructure of the fabricated composites revealed properly distributed SiC particles in the aluminum matrix. Mechanical properties of the Al–SiC P composites were investigated by the tensile test. The results proved that by increasing ARB cycles the tensile strength of the produced composites increases, but their ductility at first decreases and then increases.

Ultrafine equiaxed-grain Ti/Al composite produced by accumulative roll bonding

Ti/Al multilayered composite, mainly composed of ultrafine equiaxed grains with a mean size of 200–300 nm, has been successfully synthesized by accumulative roll bonding (ARB). The microstructure evolution and mechanical properties of the multilayered Ti/Al composite are reported. It was found that large applied shear strain, high strain rate, strain path and the low thermal conductivity of titanium are critical factors for the formation of ultrafine equiaxed grains in Ti/Al multilayered composite during the ARB process.

The Effect of Severe Plastic Deformation on the Brittle-Ductile Transition in Low Carbon Steel

Brittle-ductile transition (BDT) behaviour was investigated in low carbon steel deformed by an accumulative roll-bonding (ARB) process. The temperature dependence of its fracture toughness was measured by conducting four-point bending tests at various temperatures and strain rates. The fracture toughness increased while the BDT temperature decreased in the specimens deformed by the ARB process. Arrhenius plots between the BDT temperatures and the strain rates indicated that the activation energy for the controlling process of the BDT was not changed by the deformation with the ARB process. It was deduced that the decrease in the BDT temperature by grain refining was not due to the increase in the dislocation mobility controlled by short-range barriers. Quasi-three-dimensional simulations of dislocation dynamics, taking into account of crack tip shielding due to dislocations, were performed to investigate the effect of a dislocation source spacing along a crack front on the BDT. The simulation indicated that the BDT temperature is decreased with decreasing in the dislocation source spacing. Molecular dynamics simulations revealed that moving dislocations were impinged against grain boundaries and were reemitted from there with increasing strain. It indicates that grain boundaries can be new sources in ultra-fine grained materials, which increases toughness at low temperatures.

Aluminum tailored heat treated blanks

Tailored Heat Treated Blanks (THTB) are blanks, which exhibit locally different material properties optimized for the succeeding sheet metal forming process. The distribution of the material properties is obtained by a local, short-term heat treatment. As a result of the optimized property gradients in the sheet metal’s plain, THTB allow enhancing the forming limits significantly. The research work covered in this paper focuses on THTB made out of aluminum alloys. The article presents the microstructural mechanisms due to a short-term heat treatment as well as design principles for the heat treatment layout for THTB made out of AlMgSi alloys and ultra-fine grained (UFG) aluminum alloys produced by the Accumulative Roll Bonding process.

Nano-grained 70/30 brass strip produced by accumulative roll-bonding (ARB) process

Accumulative roll-bonding process is the only severe plastic deformation (SPD) process using rolling deformation itself, and has been used for 70/30 brass up to 6 cycles at ambient temperature under unlubricated conditions. Microstructural characterizations were done by transmission electron microscopy (TEM). After 6 cycles it was found that continuous recrystallization occurred and the microstructure covered with small recrystallized grains with an average diameter below 100 nm. The tensile tests and Vickers macro- and microhardness were conducted on the ARBed 70/30 brass. A scanning electron microscopy (SEM) study was performed in order to observe the shear bands and also to clarify the failure mechanism. The tensile strength and hardness became two and three times greater than the initial value respectively. However, the elongation dropped abruptly at the first cycle, then increased slightly. Strengthening in ARBed 70/30 brass explained by strain hardening in the first step and grain refinement at high strains. Observations revealed that the failure mode in ARBed 70/30 brass was a shearing ductile rupture with elongated shallow shear dimples.

Evaluation of mechanical properties and structure of multilayered Al/Ni composites produced by accumulative roll bonding (ARB) process

Multilayered Al/Ni composites were produced by accumulative roll bonding (ARB) process using Al 1060 and commercial Ni foils. In this process it was observed that nickel layers necked and fractured as accumulative roll bonding passes increased. After six ARB passes, a multilayered Al/Ni composite with homogeneously distributed fragmented nickel layers in aluminum matrix was produced. Structure and mechanical properties of these multilayer composites were evaluated at different passes of ARB process. During ARB, it was observed that as the strain increased with the number of passes, the strength, microhardness and elongation of produced composites increased as well. In addition, enhancement of the strength was shown to be higher than the tensile strength of Al/Al and Al/Cu multilayered composites produced by ARB process in the previous works by the same authors.

Formation of Ultrafine Grains in Cu-Fe-P Alloy by Accumulative Roll-Bonding Process

Formation of Ultrafine Grains in Cu-Fe-P Alloy by Accumulative Roll-Bonding Process

Evaluation of Texture and Grain Size of Nanograined Copper Produced by the Accumulative Roll Bonding Process

Pure copper was intensely deformed by accumulative roll bonding (ARB) for up to eight cycles at ambient temperature. X-ray diffraction (XRD) was used to evaluate the grain size and texture during the ARB process. The Williamson–Hall method was used to calculate the grain size from the XRD patterns, which was about 30 nm after eight cycles of the ARB process. Texture analysis revealed cube texture in the initial copper. The intensity of cube texture decreased after one cycle of the ARB process. The texture of two-cycle ARB-processed sample was a transition texture, from cube to shear texture (rotated cube) that appeared after two cycles of ARB process in the subsurface regions. This shear texture developed due to shear deformation induced by the high level of friction between the rolls and the sheet. Moreover, shear texture was replaced by recrystallization texture (cube component) by annealing the ARB-processed samples. This result was caused by preferential growth of cube grains.