Carbon Fiber Breakage Mechanism in Aluminum(Al)/Carbon Fibers(CFs) Composite Sheet during Accumulative Roll Bonding(ARB) Process

We put forward a method of fabricating Aluminum(Al)/carbon fibers(CFs) composite sheets by the accumulative roll bonding(ARB) method. The finished Al/CFs composite sheet has CFs and pure Al sheets as sandwich and surface layers. After cross-section observation of the Al/CFs composite sheet, we found that the CFs discretely distributed within the sandwich layer. Besides, the tensile test showed that the contribution of the sandwich CFs layer to tensile strength was less than 11% compared with annealed pure Al sheet. With ex-situ observation of the CFs breakage evolution with-16%,-32%, and-45% rolling reduction during the ARB process, the plastic instability of the Al layer was found to bring shear damages to the CFs. At last, the bridging strengthening mechanism introduced by CFs was sacrificed. We provide new insight into and instruction on Al/CFs composite sheet preparation method and processing parameters.

Enhanced mechanical properties of lamellar Cu/Al composites processed via high-temperature accumulative roll bonding

Cu/Al multilayers were produced by high-temperature accumulative roll bonding(ARB)methods up to three passes.To achieve a high bonding strength,prior to ARB processing,the Cu and Al sheets were heated to 350,400,450 and 500 ℃,respectively.The mechanical properties were evaluated by tensile tests.The microstructure was examined by optical microscopy and scanning electron microscopy equipped with energy dispersive spectrometry.The ultimate tensile stress,the grain size and the thickness of diffusion layer of lamellar composites increase with rolling temperature.When the rolling temperature is 400 ℃,the laminates show the highest ductility,but the yield stress is the lowest.As the rolling temperature further increases,both the yield stress and the ultimate tensile stress increase and the ductility decreases slightly.The mechanical properties of lamellar composites processed by low and high temperature ARB are determined by grain size and the thickness of diffusion layer,respectively.

Microstructure and mechanical properties of SiC-particle-strengthening tri-metal Al/Cu/Ni composite produced by accumulative roll bonding process

In this study, a multilayer Al/Ni/Cu composite reinforced with Si C particles was produced using an accumulative roll bonding(ARB) process with different cycles. The microstructure and mechanical properties of this composite were investigated using optical and scanning microscopy and hardness and tensile testing. The results show that by increasing the applied strain, the Al/Ni/Cu multilayer composite converted from layer features to near a particle-strengthening characteristic. After the fifth ARB cycle, a composite with a uniform distribution of reinforcements(Cu, Ni, and SiC) was fabricated. The tensile strength of the composite increased from the initial sandwich structure to the first ARB cycle and then decreased from the first to the third ARB cycle. Upon reaching five ARB cycles, the tensile strength of the composite increased again. The variation in the elongation of the composite exhibited a tendency similar to that of its tensile strength. It is observed that with increasing strain, the microhardness values of the Al, Cu, and Ni layers increased, and that the dominant fracture mechanisms of Al and Cu were dimple formation and ductile fracture. In contrast, brittle fracture in specific plains was the main characteristic of Ni fractures.

Fabrication of ultrafine-grained AA1060 sheets via accumulative roll bonding with subsequent cryorolling

Ultrafine-grained(UFG)AA1060 sheets were fabricated via five-cycle accumulative roll bonding(ARB)and subsequent three-pass cold rolling(298 K),or cryorolling(83 K and 173 K).Microstructures of the aluminum samples were examined via transmission electron microscopy,and their mechanical properties were measured via tensile and microhardness testing.Results indicate that ultrafine grains in ARB-processed sheets were further refined by subsequent rolling,and the grain size became finer with reducing rolling temperature.The mean grain size of 666 nm in the sheets subjected to ARB was refined to 346 or 266 nm,respectively,via subsequent cold rolling or cryorolling(83 K).Subsequent cryorolling resulted in ultrafine-grained sheets of higher strength and ductility than those of the sheets subjected to cold rolling.

Strength prediction of multi-layered copper-based composites fabricated by accumulative roll bonding

This work aims to evaluate the feasibility of the fabrication of nanostructured Cu/Al/Ag multi-layered composites by accumulative roll bonding(ARB),and to analyze the tensile properties and electrical conductivity of the produced composites.A theoretical model using strengthening mechanisms and some structural parameters extracted from X-ray diffraction is also developed to predict the tensile strength of the composites.It was found that by progression of ARB,the experimental and calculated tensile strengths are enhanced,reach a maximum of about 450 and 510 MPa at the fifth cycle of ARB,respectively and then are reduced.The electrical conductivity decreased slightly by increasing the number of ARB cycles at initial ARB cycles,but the decrease was intensified at the final ARB cycles.In conclusion,the merit of ARB to fabricate this type of multi-layered nanocomposites and the accuracy of the developed model to predict tensile strength were realized.

Texture evaluation in AZ31/AZ31 multilayer and AZ31/AA5068 laminar composite during accumulative roll bonding

This article presents the texture development of magnesium AZ31 alloy in the accumulative roll bonded(ARB) AZ31/AZ31 multilayer and AZ31/AA5086 laminate composite.The comparative study demonstrates that the texture evolution in AZ31 in a multilayer system is strongly influenced by the interfaces.A typical basal texture of AZ31 has been observed in AZ31/AZ31 multilayer with texture intensity increased with the rolling deformation.Presence of AZ31/AA5086 interface in the laminate composite leads to a tilted basal texture along the rolling direction(RD) in AZ31 alloy.The texture intensity of composite increased initially with rolling reduction and weakened at the higher rolling strain.Weakening of texture in AZ31 during the laminate processing at higher strain has been attributed to the development of wavy interfaces in AZ31/AA5086 laminate.

Improving mechanical properties of Mg-Al-Zn alloy sheets through accumulative roll-bonding

Experiments were conducted to evaluate the potential for improving the mechanical properties of Mg-Al-Zn alloy at room temperature by subjecting to accumulative roll-bonding(ARB).It is shown that ARB may be applied successfully to Mg-Al-Zn alloy at elevated temperatures and it leads to grain refinement and significant improvements in the ductility.The strength of the as-rolled Mg-Al-Zn alloy sheet after ARB processing is slightly decreased and basal texture is weakened by ARB processing.

Recrystallized microstructural evolution of UFG copper prepared by asymmetrical accumulative rolling-bonding process

Copper sheet with grain size of 30-60μm was processed by plastic deformation of asymmetrical accumulative rolling-bonding(AARB)with the strain of 3.2.The effects of annealing temperature and time on microstructural evolution were studied by means of electron backscattered diffraction(EBSD).EBSD grain mapping,recrystallization pole figure and grain boundary misorientation angle distribution graph were constructed,and the characteristics were assessed by microstructure,grain size,grain boundary misorientation and texture.The results show that ultra fine grains(UFG)are obtained after annealing at 250℃ for 30?40 min.When the annealing is controlled at 250℃for 40 min,the recrystallization is finished,a large number of small grains appear and most grain boundaries consist of low-angle boundaries.The character of texture is rolling texture after the recrystallization treatment,but the strength of the texture is faint.While second recrystallization happens,{110}<1ī2>+{112}<11ī> texture component disappears and turns into{122}<212>cube twin texture component.

Investigating of the Microstructure and Mechanical Properties of Al-Based Composite Reinforced with Nano-Trioxide Tungsten via Accumulative Roll Bonding Process

In the present investigation, an Al/WO3p metal matrix nanocomposite was fabricated by accumulative roll bonding (ARB) technique. Microstructural evaluation and mechanical properties of specimens were studied by Field Emission-Scanning Electron Microscopy, X-ray Diffraction, microhardness and tensile test. Several factors that affect uniform distribution of reinforcing particles were investigated. At the initial stages of ARB process particle free zones as well as particle clusters were observed in the microstructure of the composite. After 12 ARB cycles, a nanocomposite with a uniform distribution of nanoparticles was produced. It was shown that the tensile strength of the ARBed composite enhanced with the increasing number of ARB cycles. After the first cycle, a significant increase was observed in the tensile strength of nanocomposite in 2.0 percent volume of WO3p, from 89 MPa to 128 MPa (almost 1.4 times increase in strength). After the final cycle, the tensile strength value increased to 205 MPa (that is almost 2.3 times increase in strength) due to the strain hardening and grain refinement. The X-ray diffraction results showed that Al/WO3p nanocomposite with the average crystallite size of 41 nm was successfully attained after 12 cycles of the ARB process. Finally, observations revealed that the fracture mode in Al/WO3p nanocomposite was of type shearing ductile fracture with elongated shallow dimples.

Fabrication of AZ31/Mg3Y Composites with Excellent Strength and Plasticity via Accumulated Rolling Bonding and Diffusion Annealing

AZ31/Mg3Y composites with a layer thickness of 100-200μm were fabricated by accumulated rolling bonding(ARB),which was followed by diffusion annealing at 300℃ for 0-32 h.An interface layer,containing numerous Al-Y precipitates,is formed in the Mg3Y layer that is adjacent to the interface as a result of Al diffusing from the AZ31 layers into the Mg3Y layers.The thickness of the interface layer gets increased and more precipitates are formed in the interface layer with the extension of the annealing time.The microhardness of the AZ31 and Mg3Y layer decreases firstly and then reaches a stable value,while the microhardness of the interface layer increases gradually with the extension of the annealing time.The AZ31/Mg3Y composites exhibit equivalent strength but increased ductility after diffusion annealing,in comparison to the as-rolled AZ31/Mg3Y composite.In addition,the AZ31/Mg3Y composites after annealing always present higher strength and ductility than AZ31/AZ31 composite,which was fabricated by the same process as that for the AZ31/Mg3Y composites.Hetero-deformation induced strengthening also plays an important role in the excellent strength and ductility of the annealed AZ31/Mg3Y composite.This study can provide a direction for improving the plasticity and strength of magnesium alloys synergistically.

Preparation of Fe-Al Binary System Intermetallic Compounds by Multi-Layered Roll-Bonding

Iron aluminides exhibit good resistance to high-temperature sulfidizing and oxidizing environments and potential for structural applications at high temperatures under corrosive environments. In this study, Fe-Al intermetallic compound was prepared by multi-layered roll-bonding of elemental Fe and Al foils. The process consisted of the accumulative roll-bonding (ARE) for making a laminated Fe/Al sheet and the subsequent heat treatment promoting a solid phase reaction in the laminated Fe/Al sheet. The microstructures produced at each processing stage were characterized by optical microscopy and scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS). Vickers microhardness testing was used for hardness determination. A homogeneous intermetallic compound of Fe3Al or FeAl could be obtained after the subsequent heat treatment for 1.8 ks at 973 K and for 10.8 ks at 1123 or 1173 K.

Effect of annealing treatment on microstructure and mechanical properties of Al/Ni multilayer composites during accumulative roll bonding (ARB) process

Al/Ni multilayer composites are produced by accumulative roll bonding process and then annealed with different temperatures and time.Macroscopic images,microstructure and mechanical properties of Al/Ni multilayer composites are investigated.As for the macroscopic images,although there was an edge crack along the rolling direction at the third pass,the defect of composites was not serious and the forming quality of composites was relatively good.The yield strength and elongation of Al/Ni multilayer composites are improved after the annealing treatment;however,with the increase in annealing temperature and time,the yield strength and ciongation of Al/Ni multilayer composites are decreased.During the process of annealing treatment,aluminum atoms diffuse in the way of vacancy diffusion,which results in the formation of Al3Ni intermetallic phase at Al/Ni interface and Kirkendall void in the aluminum side.The content of Al3Ni intermetallic phase and Kirkenckill void would increase with the increase in annealing temperature and time.

Influence of the Accumulative Roll Bonding Process Severity on the Microstructure and Superplastic Behaviour of 7075 Al Alloy

The 7075 Al alloy was processed by accumulative roll bonding （ARB） at 350 ℃ using 2：1, 3：1 and 4：1 thickness reductions per pass （Rp） up to 8, 6 and 3 passes, respectively. Microstructural examinations of the processed samples revealed that ARB leads to a microstructure composed of equiaxed crystallites with a mean size generally lower than 500 nm. It was found that, due to both the stored energy through- out the processing and the particle pinning effect, the alloy is affected by discontinuous recrystallisation during the inter-pass heating stages, the precise microstructural evolution being dependent on Rp. Me- chanical testing of the ARBed samples revealed that the main active deformation mechanism in the ARBed samples in the temperature range from 250 to 350 ℃ at intermediate and high strain rates is grain bound- ary sliding, the superplastic properties being determined by both the microstructure after ARB and its thermal stability.

Microstructures and Mechanical Properties of Al/Mg Alloy Multilayered Composites Produced by Accumulative Roll Bonding

Al/Mg alloy multilayered composites were produced successfully at the lower temperature（280 C） by accumulative roll bonding（ARB） processing technique.The microstructures of Al and Mg alloy layers were characterized by scanning electron microscopy and transmission electron microscopy.Vickers hardness and three-point bending tests were conducted to investigate mechanical properties of the composites.It is found that Vickers hardness,bending strength and stiffness modulus of the Al/Mg alloy multilayered composite increase with increasing the ARB pass.Delamination and crack propagation along the interface are the two main failure modes of the multilayered composite subjected to bending load.Strengthening and fracture mechanisms of the composite are analyzed.

Enhanced Electromagnetic Interference Shielding in a Duplex-Phase Mg-9Li-3Al-1Zn Alloy Processed by Accumulative Roll Bonding

High electromagnetic shielding performance was achieved in the Mg-9Li-3Al-1Zn alloy processed by accumulative roll bonding(ARB).The microstructure,electromagnetic interference shielding effectiveness(SE) in the frequency of 30-1500 MHz and mechanical properties of the alloy were investigated.A model based on the shielding of the electromagnetic plane wave was used to theoretically discuss the EMI shielding mechanisms of ARB-processed alloy.Results indicate that the SE of the material increases gradually with the increase in the ARB pass.The enhanced SE can be attributed to the obvious microstructure orientation caused by ARB,and the alternative arrangement of alpha(Mg) phase and beta(Li)phase.In addition,with the increase in ARB pass,the number of interfaces between layers increases and the grain orientation of each layer tends to alignment along c-axis,which is beneficial to the reflection loss and multiple reflection loss of the incident electromagnetic wave.

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 codeformation 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 {1120} fiber texture was developed in Ti layers, while significant brass-type textures were developed in Cu layers. Some orientations along the {1120} 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 {1120} fiber texture in Ti layers.

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

Ultrafine-grain and high-strength Mg-SLi-1Al sheets were prepared by accumulative roll bonding （ARB） process. Evolution of microstructure and mechanical properties of ARB-processed Mg-5Li-1Al sheets was investigated. Results show that, during ARB process, the evolution of deformation mechanism oft Mg-5Li-1Al alloy is as follows： twinning deformation, shear deformation, forming macro shear zone, and finally dynamic recrystallization （DRX）. The grain refining mechanism changes from twin DRX to rotation DRX. With the increase in ARB cycles, strength of the Mg-5Li-1Al sheets is enhanced, whilst elongation varies slightly. With the increase in rolling cycles, anisotropy of mechanical properties decreases. It is conclusive that strain hardening and grain refinement dominate the strengthening mechanism of Mg-5Li-1Al alloy.

Development of through-thickness texture gradient and persistence of shear-type textures during annealing of commercial purity aluminium sheet processed by accumulative roll-bonding

Ultrafine-grained commercial-purity aluminum（AA1070） sheets produced by four cycles of accumulative roll-bonding（ARB） without lubrication are subjected to annealing treatments in the temperature range from 250℃ to 400℃.Microstructures and microtextures in the surface and center regions of the ARBed and annealed sheets are measured by electron backscatter diffraction.The results show that annealing treatments at 325℃ or above lead to a reduction in the microstructure gradient but a significant through-thickness texture gradient different from that in the as-deformed state.The center region is featured by the development of a strong cube texture at the expense of rolling components.In the surface region,shear-type components are either enhanced or largely retained,showing a high persistency upon annealing.While the grain structures are restored predominantly by continuous recrystallization in the surface region,a mixture of continuous and discontinuous recrystallization is envisaged for the center region.

Maintaining nano-lamellar microstructure in friction stir welding (FSW) of accumulative roll bonded (ARB) Cu-Nb nano-lamellar composites (NLC)

Accumulative roll bonded （ARB） Copper Niobium （Cu-Nb） nano-lamellar composite （NLC） panels were friction stir welded （FSWed） to evaluate the ability to join panels while retaining the nano-lamellar structure. During a single pass of the friction stir welding （FSW） process, the nano-lamellar structure of the parent material （PM） was retained but was observed to fragment into equiaxed grains during the second pass. FSW has been modeled as a severe deformation process in which the material is subjected to an instantaneous high shear strain rate followed by extreme shear strains. The loss of the nano-lamellar layers was attributed to the increased strain and longer time at temperature resulting from the second pass of the FSW process. Kinematic modeling was used to predict the global average shear strain and shear strain rates experienced by the ARB material during the FSW process. The results of this study indicate that through careful selection of FSW parameters, the nano-lamellar structure and its associated higher strength can be maintained using FSW to join ARB NLC panels.

Processing of AZ31 magnesium alloy by accumulative roll-bonding at gradient temperature

In the present investigation a wrought magnesium alloy AZ31 was successfully processed by the accumulative roll-bonding （ARB） at gradient temperature up to six cycles with the lowest temperature of 250 °C. This is performed through different thermomechanical processing routes （different ARB cycles at different temperatures of 350-200 °C）. The microstructures and mechanical properties were investigated. The results indicate that significant grain refinement is observed after the first two cycles at the highest ARB temperature as a result of dynamic recrystallization, which is necessary for the subsequently ARB cycles at relatively lower temperature with the aim to restrict grain growth. No significant finer grain size was observed through the fifth and sixth cycles while the microstructure homogeneity is further improved. The grain structure can be effectively refined at lower ARB processing temperature and higher cycles. The resulting material exhibited high strength and relatively high ductility at ambient temperature when ARB deformed above 250 °C. The mechanical properties of the ARB deformed materials are strongly dependent on several main factors： the amount and the homogeneity of strain achieved, grain size and microstructure homogeneity, textures developed during ARB and interface bonding quality.