Increasing Accumulative Roll Bonding Cycles Research Articles

On the microstructure and texture of intermetallics in Al/Mg/Al multi-layer composite fabricated by Accumulative Roll Bonding

The microstructure and texture of the intermetallics in Al/Mg/Al multi-layer composite fabricated by Accumulative Roll Bonding (ARB) at 400 °C up to 6 cycles were investigated using Electron BackScatter Diffraction (EBSD) and Synchrotron X-ray Diffraction (SXRD). EBSD and SXRD analysis have shown that ARB processing leads to the formation of Al3Mg2 and Mg17Al12 intermetallics soon after the second ARB cycle with a global thickness of 12 (N = 2) to 22 µm (N = 6). The polycrystalline intermetallics plates growth was columnar and normal to the bonding interface. A constitutional liquefaction region was depicted ahead of the plates with an unusual rugged migration front. The Al3Mg2 and Mg17Al12 intermetallic compounds which formed after 2 ARB cycles have approximately the same average grain size (1.0 µm) at this cycle. After 4 ARB cycles, the grain refinement of Al3Mg2 is more than 4 times higher than in Mg17Al12. The average grain size of Al3Mg2 and Mg17Al12 reach 0.2 and 0.9 µm, respectively. After 6 cycles of ARB, the average grain size of both Al3Mg2 and Mg17Al12 increased to 1.5 µm and 2.8 µm, respectively. The dislocation density obeyed a ρAl3Mg2 > ρAZ31 > ρAl 1050 ∼ ρMg17Al12 hierarchy after N = 4 and 6 ARB cycles and the Al3Mg2 was shown to store more dislocations. Through the ARB processing, a usual strong basal (0002) texture was depicted in AZ31 layers and a weak rolling texture was shown in Al 1050 layers with a dominant Rotated Cube (001) 110 > component that vanished after upon increasing ARB cycles. The Al3Mg2 and Mg17Al12 intermetallics were characterized by a random texture.

Mechanical properties and fracture surface of Al-Al2O3 nano/micro-composites produced by accumulative roll bonding

ABSTRACT The accumulative roll bonding (ARB) process has been utilised to produce layered materials and composites with high strength without intermediate annealing steps. This study focused on the size of reinforced particles (Al2O3) with an average size of 3 µm (m) and 80 nm (n) in aluminum matrix composites. Three different samples of monolithic Al, Al-1 vol.% (m)Al2O3, and Al-1 vol.% (n)Al2O3 particulate composites were produced by ARB. The SEM results revealed that the distribution of alumina particles in the fabricated composites was improved with increasing ARB cycles, while the Al-1 vol.% (m)Al2O3 composite presented the proper distribution of particles at higher cycles in contrast with the Al-1 vol.% (n)Al2O3 composite. The tensile strength of the produced composites was enhanced, and their ductility decreased with the increase in ARB cycles, while Al-1 vol.% (m)Al2O3 with a tensile strength of 253 MPa showed higher strength than Al-1 vol.% (n)Al2O3 with 229 MPa at the sixth cycle. By adding Al2O3 microparticles, the yield strength and tensile strength of the microcomposite sheet were increased to about 5 and 2.1 times, respectively, compared to the Al sheet.

Effects of repeated accumulative roll bonding cycles on microstructural characteristics and tensile behaviors of Al2O3 particle reinforced aluminum-matrix composites

The effects of repeated accumulative roll bonding (ARB) cycles on reinforcement phase features, matrix microstructure and composite tensile behavior evolution were investigated by microscopy, machine learning, tensile testing, and fracture surface observation. The results showed that with increasing ARB cycles, the reinforcement particles decohered and their distribution uniformity improved. Meanwhile, the matrix microstructure evolved and consequently, the mechanical properties of the composite were improved. However, all parameters saturated at higher ARB cycles suggesting the limitation of further cycles in strengthening composites. These findings are significant for enhancing the knowledge about the microstructure and mechanical properties of particle reinforced composite and optimizing the fabrication of composites by ARB.

Structural and corrosion behavior investigation of novel nano-quasicrystalline Al-Cr-Fe reinforced Al-matrix composites produced by ARB process

In the present study, aluminum metal matrix composites (AMCs) reinforced with Al-Cr-Fe quasicrystal (AlQC) nanoparticles (3 and 5 wt%) and monolithic Al were produced by the accumulative roll bonding (ARB) process up to 8 cycles. X-ray diffraction (XRD) and scanning electron microscopy were employed for structural evaluation. XRD results confirmed the presence of AlQC nano-powders in the Al matrix and the decrease of the matrix crystallite size to a nanometric scale (105 nm) after eight cycles. Microstructural studies showed an improvement in the distribution of the AlQC nanoparticles in the matrix, as well as the connection improvement between Al layers by increasing ARB cycles. Density measurements also showed that theoretical density of the composite samples was greater than the measured density, which is attributed to the presence of voids and pores. Also, corrosion behavior investigations in 3.5 wt% NaCl solution showed that corrosion potential decreases and corrosion rate increases in the presence of AlQC nanoparticles as the reinforcement in comparison to monolithic Al. Finally, a decrease in the corrosion rate of the samples was realized by increasing ARB cycles to the 4 cycle and then an increase was detected by further increasing cycles up to 8 cycles.

Micromechanical behavior of multilayered Ti/Nb composites processed by accumulative roll bonding: An in-situ synchrotron X-ray diffraction investigation

Heterophase interfaces play a crucial role in deformation microstructures and thus govern mechanical properties of multilayered composites. Here, we fabricated Ti/Nb multilayers by accumulative roll bonding (ARB) where shear bands became predominant with increasing rolling cycles. To explore correlation between micromechanical behavior and mechanical properties of the composites with various lamellar morphologies, in-situ high-energy X-ray diffraction tensile tests were performed. The results quantitatively reveal that the rapid strengthening of the composites with increasing ARB cycles mainly originates from the Nb layers strengthened by dislocations, grain boundaries and heterophase interfaces, and the {211} grains mostly contribute to the global strain hardening. The softer Ti grains also extend global strain hardening to a wide range and postpone necking. Furthermore, complete stress state analysis show that in the presence of extensive shear bands, significant load partitioning between the neighboring metals leads to triaxial stresses in each constituent and dislocations tend to slip along the shear direction. This promotes dislocation multiplication and motion, which is conducive to overall strength enhancement while maintaining a satisfactory ductility. These findings elucidate the effect of strong constraints of the interfaces on mechanical properties, which provides a fundamental understanding of load partitioning and strengthening mechanisms of the multilayers processed by multiple ARB cycles.

Revealing hetero-deformation induced (HDI) stress strengthening effect in laminated Al-(TiB2+TiC)p/6063 composites prepared by accumulative roll bonding

Laminated metal composites as a type of heterostructured materials, consisting of two or more metals, have attracted extensive attention for their excellent mechanical properties, electrochemistry characteristics and corrosion resistance. In this study, an Al-(TiB2+TiC)p/6063 laminated composite was successfully prepared for the first time using accumulative roll bonding (ARB) process up to three cycles. The particle distribution in Al-(TiB2+TiC)p layer became more dispersive with the increasing ARB cycles and the matrix α-Al grains were also refined significantly. The interfaces of 6063 and Al-(TiB2+TiC)p layers were well bonded and kept straight without any necking or fracture during the plastic deformation. The tensile strength and ductility of the laminated composites were increased simultaneously with increasing ARB cycles. Ultimate tensile strength, yield stress and elongation to failure of the composites increase to 255.8 MPa, 247.4 MPa and 11.6% after three ARB cycles, increased by 21.9%, 22.4% and 17.2%, respectively. It is revealed that hetero-deformation induced (HDI) stress played a crucial role in significant enhancement of tensile strength and ductility for the laminated composites.

Effect of Microstructure Refinement on Hardness Homogeneity of Aluminum Alloy 1100 Processed by Accumulative Roll Bonding

This work examines the effect of grain refinement via accumulative roll bonding (ARB) on the homogeneity of microstructure and hardness through the thickness of commercially pure aluminum AA1100 sheets. The use of 7 cycles of ARB was shown to produce homogeneous ultrafine-grained microstructure, reducing the grain size to 0.46 and 1.03 µm in normal direction and rolling direction, respectively. Examination by electron backscattered diffraction indicates that continuous dynamic recrystallization was the main mechanism for the formation of submicron equiaxed grains bounded with high-angle grain boundaries (HAGBs). The fraction of HAGBs increased gradually reaching a maximum of 71.6% after 7 cycles. Through-thickness hardness measurements using Vickers and nanoindentation tests show an increase from 43.5 Hv (0.85 GPa) for as-received sample to 63 Hv (1.1 GPa) after 7 cycles. The heterogeneity in hardness through the thickness of the as-received material was shown to restrain the evolution of uniform hardness across the sheet thickness with increasing ARB cycles. Tensile tests showed that the tensile strength is increased to 250 MPa, which is about 2 times its initial value. Owing to the high stacking fault energy of AA1100, strong dynamic recovery occurred with increasing ARB strain which was balanced with the strain hardening property of the material. This resulted in plastic instability at small strains and thus early necking during the tensile test.

A crystal plasticity FEM study of through-thickness deformation and texture in a {112} aluminium single crystal during accumulative roll-bonding

In this study, a crystal plasticity finite element method (CPFEM) model was used to study the deformation behaviour in an aluminium single crystal (1 1 2)[1 1 -1] processed by accumulative roll-bonding (ARB) up to 9 cycles. The simulation followed the real ARB process based on the developed finite element model. The predicted through-thickness texture matches well with the experimental observations. The deformation behaviours, in terms of crystal rotation, shear strain and slip system activation, in the first and second cycles (conventional rolling) were unidirectional, but the deformation was altered after ARB was applied from the third cycle onwards. Such alteration was found to be caused by the thickness position change and deformation discontinuity at interfaces, which were investigated in detail. The role that interfaces play became dominant over thickness position change as increasing ARB cycles.

Microstructural and textural evolutions in multilayered Ti/Cu composites processed by accumulative roll bonding

Ti/Cu multilayered composites were fabricated via accumulative roll bonding (ARB). During co-deformation of the constituent metals, the hard Ti layers necked preferentially and then fragmented with the development of shear bands. Transmission electron microscopy showed that with increasing ARB cycles, grains in Ti were significantly refined even though dynamic recrystallization has occurred. For Cu the significant grain refinement was only found within the shear banded region when the composite was processed after five ARB cycles. Due to the diffusion of Cu atoms into Ti at the heterophase interfaces, amorphization with a width less than 10 nm was identified even in the composite processed by one cycle. At higher ARB cycles, the width of amorphous region increased and intermetallic compounds CuTi appeared from the region. The lattice defects introduced at the heterophase interfaces under roll bonding was responsible for the formation of the nano-scaled compounds. X-ray diffraction showed that an abnormal {112¯0} fiber texture was developed in Ti layers, while significant brass-type textures were developed in Cu layers. Some orientations along the {112¯0} fiber favored the prismatic < a> slip for Ti. Tensile tests revealed the elevated strength without a substantial sacrifice of ductility in the composites during ARB. The unique mechanical properties were attributed to the significantly refined grains in individual metals, the good bonding between the constituent metals, as well as the development of an abnormal {112¯0} fiber texture in Ti layers.

Effect of Processing Parameters on Microstructure and Mechanical Properties of Al6061/B4C Metal Matrix Composite Fabricated by Using Stir Casting, Post-Accumulative Roll Bonding and Aging Treatment

In the present research, Al6061-based composites reinforced with micron-sized B4C particles were fabricated by the combination of stir casting and post-processing via accumulative roll bonding (ARB) and aging treatment. Microstructural evolutions of processed samples were investigated using optical and scanning electron microscopy. Also, mechanical properties were studied by micro-hardness measurements and room temperature tensile testing. From obtained results, it was concluded that the as-cast composites had a lower tensile strength and elongation compared with accumulative roll-bonded counterparts. Post-processing by accumulated roll bonding decreased the deficiencies aroused during stir casting and improved particle distribution. It was observed that increasing ARB cycles decreased the particle-free zones and particle clusters.

Microstructure, texture and mechanical properties of AA 1060 aluminum alloy processed by cryogenic accumulative roll bonding

AA 1060 aluminum alloy sheet was processed to five accumulative roll bonding (ARB) cycles at cryogenic temperature. The microstructure, texture and mechanical properties of the ARB processed sheets were investigated. The results show that the surface layer of the ARB processed sheets exhibits a significant r-cube shear texture. Initial cube orientation at the surface layer was gradually rotated to the r-cube orientation during the ARB process, leading to the increase in the strength of the r-cube shear texture with ARB cycles. The texture evolution at the surface layer was quantified in terms of a simple relation between the texture volume fractions and accumulated true strain. The strength of the β fiber rolling texture and the distribution of orientation intensities along the β fiber at the center layer were strongly affected by the initial texture. As the ARB cycles increased, the initial texture was changed from the cube texture to the r-cube texture, leading to a continuous increase in the strength of the β fiber rolling texture dominated by the C orientation. The yield and ultimate tensile strength of the ARB processed sheets increased markedly after the first ARB cycle and then increased slowly with increasing ARB cycles, while the elongation decreased accordingly.

Development of Cu-matrix, Al/Mn-reinforced, multilayered composites by accumulative roll bonding (ARB)

In this work, nanostructured Cu/Al/Mn multilayered composites were successfully fabricated by the accumulative roll bonding (ARB) method. The microstructure of the produced composites was studied by X-ray diffraction and scanning electron microscopy. Also, the hardness, tensile and corrosion behaviors of the composites were studied as a function of ARB cycles. It was observed that by increasing the number of ARB cycles, the thickness of the Al layers is decreased from 0.3 mm to 0.25 μm, where a Cu-matrix, Al/Mn-reinforced, multilayered composite with homogeneously distributed Al layers and Mn particles was achieved after nine ARB cycles. Also, the results revealed the development of nanostructures with the mean crystallite size of about 50 nm in the produced composites. According to the tensile experiments, by increasing ARB cycles, the strength of the composites was increased and reached 420.8 MPa. The electrochemical corrosion behavior of the produced composites was also investigated in a 3.5 wt % NaCl solution by a potentiostat-galvanostat device. It was found that the corrosion rate of the composite is increased by increasing ARB cycles from 5 μA/cm2 to 12.2 μA/cm2 and then decreased to 9.5 μA/cm2.

Post-annealing, fractographic and corrosion failure analyses on tri-modal Mn-particulate Al/Cu multilayered composites

In this work, Mn-particulate Al/Cu multilayered (70Al/25Cu/5Mn) composites were fabricated by the accumulative roll bonding (ARB) process. Afterwards, the structure (after ARB and post-annealing) and failure (tensile fracture and corrosion in 3.5 wt% NaCl solution) studies were conducted on the specimens processed for different ARB cycles. Based on the results, no intermetallic compound was formed in the ARB-processed composites even to 9 cycles. Nonetheless, Al-Cu-(Mn) intermetallics were detected in the annealed samples, so that their amount was enhanced by increasing ARB cycle. Concerning the failure analyses, the resistance of the produced composites against corrosion and fracture, contrary to strength, was reduced by increasing ARB cycles.

High strength and damping capacity of LLZNO/Al composites fabricated by accumulative roll bonding

In order to fabricate high damping/strength metal matrix composites, hard ceramic particulates Li6.75La3Zr1.75Nb0.25O12 (LLZNO) reinforced Al composites were prepared by accumulative roll bonding (ARB) method with intermittent heat treatments. LLZNO particles did not react with Al and were uniformly dispersed in Al-matrix after 10 ARB cycles. With increasing ARB cycles, the ultimate tensile strength of the LLZNO/Al composites increased and reached 132MPa after 10 ARB cycles, which was 2.5 times that of the pure Al, while the total elongation of LLZNO/Al composites increased from 5% after 1 cycle to 10% after 10 cycles. The maximum damping capacity as high as 0.009 was achieved after 10 ARB cycles in the 10wt% LLZNO/Al composite at 320K and 1Hz, which was 4.5 times that of pure Al. The simultaneous enhancement on damping capacity, tensile strength and ductility of the LLZNO/Al composite around room temperature can be ascribed to the high damping capacity and the dispersion strengthening of the LLZNO phase, as well as the good bonding between the LLZNO particles and Al matrix resulted from the ARB technique.

Microstructure and Mechanical Properties of Multilayered Cu/Ti Composites Fabricated by Accumulative Roll Bonding

Multilayered composites composed of pure copper and titanium (Cu/Ti) have been fabricated by accumulative roll bonding (ARB). The macroscopic lamellar structures, mechanical properties and microstructures of the composites are investigated. The results show that the Cu and Ti layers are bonded well during the ARB processing. With the increasing number of ARB cycles, Ti layers start to neck, fracture and even segregate within the Cu matrix, which is attributed to the activation of shear bands that cut through the multiple metal layers. At larger ARB cycles, the distribution of small fragmentations of Ti inside the Cu matrix is more homogeneous, which is attributed to the fact that the outer surfaces of the previously processed composite are placed in the interior of the subsequent ARB stack. Tensile testing at room temperature shows that the yield strength and the ultimate strength of the composites increased mildly with the increasing ARB cycles, while the uniform elongation of the composites is retained. Microhardness tests reveal that the increase of strength in the composites during ARB mainly results from the reinforcement of the Ti layers. The mechanical behaviors of the composites can be attributed to the effect of the mixed microstructures in the both constituent metals.

Cu-(B4C)p metal matrix composites processed by accumulative roll-bonding

In this study, Cu/B4C metal matrix composites were prepared by accumulative roll-bonding (ARB). The microstructure of the processed samples was characterized by TEM, SEM and optical microscopy. The microhardness, uniaxial tensile and four-point probe tests were carried out to evaluate the mechanical properties and electrical resistivity of the ARBed monolithic and composite samples. The results showed that the reinforcement distribution was improved by increasing ARB cycles, which was quantitatively confirmed by some models. Based on TEM observations, the formation of an ultrafine grained structure in the composite matrix was also approved. It was shown that with increasing ARB cycles, the microhardness and tensile strength of the monolithic Cu samples were enhanced up to the 3rd cycle and then saturated, but the microhardness and tensile strength of the composites showed an increasing trend to the last cycle. Apart from a substantial improvement in the mechanical properties of the Cu/B4C composites, a minor decrement in electrical conductivity was detected after six ARB cycles.

Fabrication of Al/Mg/Al Composites via Accumulative Roll Bonding and Their Mechanical Properties.

Al(1060)/Mg(AZ31)/Al(1060) multilayered composite was successfully produced using an accumulative roll bonding (ARB) process for up to four cycles at an elevated temperature (400 °C). The microstructure evolution of the composites and the bonding characteristics at the interfaces between Al and Mg layers with increasing ARB cycles were characterized through optical microscopy, field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). It was found that the grains of Al and Mg layers were significantly refined and Al3Mg2 and Al12 Mg17 intermetallic compound layers formed at the Al/Mg bonding interfaces. The strength increased gradually and the ultimate tensile strength (UTS) reached a maximum value of about 240 MPa at the third pass. Furthermore, the strengthening mechanism of the composite was analyzed based on the fracture morphologies.

Microstructural evolution, mechanical properties, and strain hardening behavior of ultrafine grained commercial pure copper during the accumulative roll bonding process

In this study, the microstructural evolution, mechanical properties, and strain hardening behavior of commercial pure copper processed by the accumulative roll bonding (ARB) were investigated. Transmission electron microscopy (TEM) micrographs and atomic force microscopy (AFM) images indicated that with increasing the number of ARB cycles, the grain size of samples decreased. An Ultrafine grained (UFG) structure with an average grain size of about 200nm was achieved after four cycles of ARB. The yield and ultimate tensile strength of pure copper with the UFG microstructure was reached about 360MPa and 396MPa (about 400% and 100% higher than that of the annealed state), respectively. All ARB-processed copper samples showed lower strain hardening exponent in comparison with the annealed state. Moreover, the strain hardening rate increased with increasing ARB cycles up to 3 cycles and then decreased.

Microstructure evolution and mechanical properties of Al/Al–12%Si multilayer processed by accumulative roll bonding (ARB)

In this study, multi-layered Al/Al–12%Si composites were produced by the accumulative roll bonding (ARB) at ambient temperature using commercial pure Al 1050 and Al–12%Si alloy sheets. The microstructures of Al and Al–12%Si alloy layers were characterized by scanning electron microscopy (SEM). Vickers microhardness and tensile tests were conducted to investigate mechanical properties of the composites. It was observed that by increasing ARB cycles, thickness of individual Al and Al–12%Si alloy sheets decreased; finally, Al–12%Si layers were necked at the second cycle. After the second ARB cycle, a multi-layered Al/Al–12%Si composite with homogeneously distributed Al–12%Si layers in aluminum matrix was produced. Si phase was refined from 65.6 to 25.57µm in length and the Al grain size was reduced from 25 to 7.2μm. The formation of Al3.21Si0.47 intermetallic phase after the second cycles was confirmed by X-ray diffraction. The results showed that the tensile strength increased up to 270MPa after first cycle and dropped afterwards. Microhardness measurement indicated that hardness of individual layers increased continuously with increasing the ARB cycles.

Properties of high specific strength Al–4 wt.% Al2O3/B4C nano-composite produced by accumulative roll bonding process

The influence of nano-scale reinforcement on the mechanical and microstructural properties of ultrafine-grained composites was studied. Al matrix (pure aluminum) composites, with a grain size of 230nm and B4C and Al2O3 reinforcements with an average size of 50nm, were fabricated via the accumulative roll bonding (ARB) process. To evaluate structure and microstructure of the produced composites, X-ray diffraction analysis (XRD) and transmission electron microscopy (TEM) were applied. Mechanical properties of the specimens were investigated by tensile and hardness tests. The result revealed that in comparison with monolithic Al (ARBed Al without ceramic particles), the presence of nano-particles enhances specific strength of composites. Also, the results showed that with increasing ARB cycles, the microhardness of the composites increases. In addition, the specific strength and microhardness of the composite samples are higher than those of the monolithic Al. The density of the composite samples and monolithic Al was measured by the Archimedes method showing that the density decreases in presence of ceramic particles.