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In this study, novel composite strips based on 2017A-T4 aluminium alloy (Al-Cu-Mg) produced by accumulative roll bonding (ARB) were developed. The microstructure and mechanical properties of the ultrafine-grained sheets under quasistatic and dynamic loadings were investigated. The initial microstructure characterization with an Optical Microscope and a Scanning Electron Microscope indicated that the ARBed sheets formed a compact material with the homogeneous and identical thickness for the individual bonded layers. Besides, the presence of precipitates was identified in all the processed strips with diverse sizes, quantities and distribution. Moreover, from Electron Back Scatter Diffraction, the microstructure was noticeably refined with increasing theARBcycles to reach 1.7 mof the grain size at the fifth cycle. The microhardness measurement and the tensile test were carried out for both natural ageing and ARBed specimens. Accordingly, the tensile stress acts on the individual layers rather than the entire sample that conduct to a reduction in the overall properties for the ARBed strips. Furthermore, a stabilization in the mechanical properties for the three first ARB cycles was noted, whereas, the domination of the dynamic recrystallization was responsible for a significant drop after the fourth cycle which is considered as the transition state. The characteristics of the compression deformation were examined under dynamic and quasi-static loadings conditions by using the Split-Hopkinson Pressure Bar system and the universal testing machine, respectively. The strain hardening behaviour was investigated using the Hollomon analysis. It was found that the thermal softening played a crucial role when compared to the strain hardening for all the studied strips. Moreover, the strain rate under the dynamic loading has a minor effect on the stress flow of the ARBed sheets compared to the as-received material. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract In this paper, an accumulative roll bonding (ARB) process is exploited to produce high-strength, fine dispersed and uniform distribution of Al-5vol.%SiC nanocomposite. The microstructure illustrates and validates a good distribution of SiC reinforced in the Al 1050 matrix. It is observed that, an increasing of ARB passes tends to decrease and refine the size of SiC particle to nanoscale. It is concluded from tensile test that, as number of passes increases, strengths of Al ARBed and composite samples are improved. However, their ductility decreases at initial ARB pass and then increased. The Al-SiC tensile strength of nanocomposite sample is greater 5 times than the annealed Al 1050 used as the original raw material. The strengthening of composite sample occurs due to grain refinement, uniformity, reinforcing role of particles, strain work hardening, and bonding quality. From hardness test, after the initial pass, the hardness improved quickly, then dwindled and finally saturated by further rolling. Experimental data is exploited to derive governing equations describe the effect of the number of ARB passes on the tensile strength and elongation of manufactured nanocomposite samples. It is found that, the tensile strength and elongation can be described as an exponential function that depends on the number of passes. Numerical results from these equation are more consistent with experimental investigation. Highlights • ARB technique is used to produce highly uniform Al-SiC nanocomposites. • The tensile strength and elongation can be described by exponential functions, those depend on the number of ARB passes. • Tensile strength and microhardness became 4 and 3 times larger than Al. • Grain refinement, dislocation strengthening are the main strengthening mechanisms. [ABSTRACT FROM AUTHOR]

In this study, the effect of accumulative roll bonding (ARB) process on the microstructure, deformation texture and mechanical properties of AA2024 strip was investigated. Microstructural observations were done by electron backscattering diffraction (EBSD) technique and scanning electron microscopy (SEM). Also, mechanical properties were performed by uniaxial tensile and microhardness tests. It was observed that accumulative roll bonding is a promising process for production of nano/ultrafine grained (NG/UFG) 2024 aluminum alloy after seventh ARB cycles, reaching grain sizes of smaller than 120 nm. The fraction of high angle grain boundaries and mean misorientation were represented increased by increasing the strain during the ARB process and reached to a saturated value of 64% and 25.37°, respectively. Deformation texture evolution demonstrated that the formation of nano shear bands at the final ARB cycle was facilitated by the formation of Brass {011}〈211〉 and Goss {011}〈100〉 components. By increasing the number of ARB cycles, the yield strength, tensile strength and microhardness of the ARB processed sample improved and reached to 345 MPa, 450 MPa and 141 HV after 7 cycles, respectively, which were 2.65, 2.40 and 2.23 times higher than obtained values for initial materials, i.e. 130 MPa, 188 MPa and 63.5 HV. After the tensile test, debonding can be observed especially in the interface formed in the last cycle. Observations revealed that the failure mode in the accumulatively roll bonded AA2024 strip was a shear ductile rupture with elongated shallow shear dimples. [ABSTRACT FROM AUTHOR]

Commercial pure Al sheets were severe plastically deformed at room temperature by accumulative roll bonding (ARB) and cross accumulative roll bonding (CARB). Change in strain path was imposed during CARB by rotating the sheets with 90° around the normal direction axis between each cycle. Microstructural evolution of processed sheets was studied by electron back scattered diffraction (EBSD) analysis and revealed that nano/ultrafine grains (NG/UFG) with the average grain size of 380 nm and 155 nm were formed by both processing routes after eight cycles, respectively. The fraction of high angle grain boundaries and mean misorientation angle of the boundaries in the CARB were 49% and 40.20°, respectively, in comparison to that of ARB sample (41% and 37.37°). Deformation texture evolution demonstrated that the change in strain path leads to the formation of strong orientation along the β-fiber. The major texture components for ARB specimens were Brass {011}<211> and S {123}<634> while those for CARB were Brass {011}<211> and Goss {011}<100>. The CARB processed specimen exhibited the tensile strength, microhardness and elongation of about 230 MPa, 92 HV and 13% compared with ARB sample (180 MPa, 80 HV and 10.5%) after eight cycles. Scanning electron microscopy (SEM) observations of tensile fracture surface of specimens revealed ductile type fracture. [ABSTRACT FROM AUTHOR]

This investigation aims to understand the differences in the recrystallization and grain growth textures in aluminum layers along the thickness direction of two layered composite sheets. The sheets were processed by five cycle accumulative roll bonding of commercially pure aluminum and an aluminum alloy containing 0.3 wt.% Sc both in the supersaturated solid solution and artificially aged conditions. Electron back scattered diffraction and transmission electron microscopy were used to characterize the microstructure and crystallography of the rolled and annealed composites. During the early stages of annealing the β-fiber rolling textures remain unchanged and becomes sustained by the so-called continuous recrystallization process. Then, at the completion of primary recrystallization in the later stages of annealing, orientation selective recrystallization occurs and the Brass orientation becomes eliminated. A strong β-fiber primary recrystallization texture was found to be favorable for the secondary recrystallization growth of Cube orientations. Otherwise, conventional grain growth occurs when the primary recrystallization textures have distortions in the β-fiber. [ABSTRACT FROM AUTHOR]

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 25.57 µm in length and the Al grain size was reduced from 25 to 7.2 μm. The formation of Al 3.21 Si 0.47 intermetallic phase after the second cycles was confirmed by X-ray diffraction. The results showed that the tensile strength increased up to 270 MPa after first cycle and dropped afterwards. Microhardness measurement indicated that hardness of individual layers increased continuously with increasing the ARB cycles. [ABSTRACT FROM AUTHOR]

Accumulative roll bonding (ARB) has been used as a severe plastic deformation process for the industrial production of ultra-fine grained (UFG) and nano-crystalline sheets with excellent mechanical properties. In the present study, the effect of the ARB process on the corrosion behavior of UFG and nano-crystalline 1050 aluminum alloy in a buffer borate solution (pH 5.5) has been investigated. The result of microhardness tests revealed that microhardness values increase with an increasing number of ARB cycles. A sharp increase in microhardness is seen after three ARB cycles, whereas moderate additional increases are observed afterward for up to nine cycles. Also, the XRD results showed that the mean crystallite size decreased to about 91 nm after nine cycles. The potentiodynamic plots show that as a result of ARB, the corrosion behavior of the UFG and nano-crystalline specimens improves, compared to the annealed 1050 aluminum alloy. Moreover, electrochemical impedance spectroscopy measurements showed that the polarization resistance increases with an increasing number of ARB cycles. [ABSTRACT FROM AUTHOR]

For the dissimilar laminated metal composite sheets (LMCS) fabricated by roll bonding technology, the great differences of mechanical properties between the constituent metals lead to the non-uniform deformation and individual layer necking. The individual layer shape affects the mechanical properties and microstructure of dissimilar LMCS. The Al/Al alloy (1100/7075) LMCS with the same thickness and ratio of dissimilar metals, but different individual layer shapes, have been successfully fabricated by hot accumulative roll bonding in conjunction with cold rolling technology. Some effective methods (such as sheet crown, warp degree, and slant angle) were presented to quantitatively evaluate the individual layer shape and necking of constituent metals. The microstructure and mechanical properties of 1100/7075 LMCS with different individual layer shapes were investigated. The effects of bonding interface on the mechanical properties were obtained based on the assessment of individual layer shapes and necking. The strength and elongation of LMCS decrease with the increase of variation of individual layer shapes and necking when the number of layers keeps constant. The research results offer some theoretical guides and references for adjusting the control measures of compatibility deformation, optimizing the hot roll bonding technologies, and designing the novel high-performance dissimilar LMCS. [ABSTRACT FROM AUTHOR]

Abstract: Wear behavior of severely deformed aluminum sheets by accumulative roll bonding (ARB) process was characterized using a pin on disc wear machine at different conditions. The sheets were processed up to eight ARB cycles in order to induce a high strain (~6.4) to the samples. EBSD results showed that after eight cycles of ARB, sheets were found to contain ultrafine grains with high fraction of high angle grain boundaries. Wear experiments were conducted under different loading and operating conditions, including dry and immersion lubrication, and rotation speeds. Wear was continuously monitored by measuring the wear rates and morphologies of worn surfaces by scanning electron microscope (SEM). Contrary to expectation, the wear resistance of the ARBed Al sheets was less than the non-processed sheets. Wear rates of the ARBed Al sheets increased by increasing wear load and rotation speed, while, immersion lubrication decreased the wear rate significantly. Based on the observation and results, a model for the wear of the ARBed Al was proposed. [ABSTRACT FROM AUTHOR]

Abstract: The plastic anisotropy of ultrafine grained aluminium alloys AA1050 and AA6016 produced by accumulative roll bonding (ARB) has been investigated by tensile deformation via the Lankford parameter. The average normal and planar anisotropies slightly increase (from 0.6 to 0.9) and decrease (from 0.6 to −0.7) as a function of ARB cycles, respectively. The global textures measured by neutron diffraction are used to simulate the Lankford and anisotropy parameters of the plates after 0, 2, 4, 6 and 8 ARB cycles with the help of the viscoplastic polycrystal self-consistent model. Simulation results are compared with those from experiment and discussed with regard to texture, strain rate sensitivity, grain shape and slip system activity. [Copyright &y& Elsevier]

Positron annihilation spectroscopy was performed in order to study the influence of preparation route and processing on atomic free volumes in amorphous and nanocrystalline aluminium alloys. In melt-spun amorphous Al88Y7Fe5, structural free volumes smaller than a lattice vacancy are predominant, whereas in amorphous Al92Sm8 prepared by repeated cold rolling larger free volumes occur. In the early stages of nanocrystallization of Al88Y7Fe5, an indication of Y enrichment at interfacial free volumes in the growth front of the Al nanocrystallites is found. [Copyright &y& Elsevier]

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-(TiB 2 +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-(TiB 2 +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-(TiB 2 +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. Image 1 • An Al-(TiB 2 +TiC) p /6063 laminated composite was prepared using ARB process. • Tensile strength and ductility were increased simultaneously with increasing ARB cycles. • The higher strain hardening rate leads to the increased ductility of the composites. • Hetero-deformation induced (HDI) hardening contributes significantly to the enhanced strength. [ABSTRACT FROM AUTHOR]