Accumulative Roll Bonding Cycles Research Articles

Revealing the evolution mechanisms of microstructure, texture and mechanical behavior in Zr702 alloy plates fabricated by accumulative roll bonding

In the present work, the influence of number of cycles on microstructure, texture and mechanical behavior of Zr702 plates has been systematically studied using the accumulative roll bonding (ARB) method. Electron back-scatter diffraction and transmission electron microscopy have been used to study the development of microstructure and texture. Results show that the {0001} bimodal texture is obvious in all the samples. At the same time, the <112‾0> fiber is weakened and the <101‾0> fiber is strengthened gradually with the increase of ARB cycle number from 1 to 3. In addition, some unbroken coarse grains with c-axis close to normal direction can be observed in ARB samples. The reason for this phenomenon is that the prismatic <a> slips are not easily activated due to unfavorable orientation. The tensile test results along the rolling direction show that the strength increases and the elongation decreases with the increase of ARB cycle number. Compared with the as-received plate sample, the yield strength of ARB sample subjected to 3 cycles is increased by about 99%, while still maintain 7.4% of the elongation to fracture. In order to clarify the mechanical mechanisms during deformation, the back stress hardening caused by the heterostructure mixed with coarse and fine grains and substructure have been discussed in detail. In addition, the calculation results of Schmid factor (SF) show that prismatic <a> slip is the dominant slip mechanism in the deformation process of all samples. However, the average SF value of the basal <a> slip systems decreases with the increasing number of ARB cycles, which maybe another significant factor leading to the change of yield strength.

The Effect of Preheating Temperature on the Forming Limit Diagram of AA1050/AA7050 Al Multilayered Sheets Produced by Accumulative Roll Bonding (ARB)

Multilayered sheets of AA1050 and AA7050 Al alloys produced by hot accumulative roll bonding (ARB) are tested to estimate their forming limit diagrams (FLDs). Sheets processed with preheating at 450 and 500 °C for up to six ARB cycles are submitted to Nakazima tests with an in situ digital image correlation system and tensile tests to analyze the mechanical behavior. X‐ray measurements and electron backscatter diffraction are performed to obtain the crystallographic texture and the mesotexture, respectively, and thus characterize the heterogeneous microstructure. A bimodal grain size distribution is observed in these sheets since AA7050 layers present elongated and fine grain size with nanometric precipitates and AA1050 layers present coarser and equiaxed grains. In addition, texture analysis indicates both rolling and shear components in the sheets. The FLDs show that the forming properties did not follow the expected rule of mixtures when compared with monolithic alloy sheets. Overall, the multilayered AA1050/AA7050 processed by means of ARB at 500 °C presents better formability than that at 450 °C, due to the combination of lower anisotropy measured by the Lankford coefficients values close to 1 and low normal anisotropy Δr values.

Feasibility study of producing Al–5Zn–1 Mg alloy by accumulative roll bonding process and subsequent heat treatment

In this research work, Al/5Zn/1Mg (wt.%) composite sheets were produced by the accumulative roll bonding (ARB) process and then converted into Al-5Zn-1 Mg (wt.%) alloy sheets by a suitable heat treatment process. Scanning electron microscopy (SEM) combined with energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) were used for structural investigations. Mechanical properties of the specimens were also examined by using tensile and microhardness measurements. SEM microstructural analyses revealed the uniform distribution of Zn layers and Mg powder particles in the Al matrix by increasing the number of ARB cycles, as well as the formation of the α phase after the seventh ARB cycle and subsequent heat treatment at 390 °C in the alloy samples. XRD results confirmed the microstructural evolution and showed only peaks related to Al for the alloy samples after the seventh cycle. Tensile results showed that by increasing the number of ARB cycles from first to seventh, tensile strength and elongation increased from 117 MPa to 370 MPa and 8 to 13 %, respectively. Microhardness measurements also depicted the progressive increase in hardness by increasing the ARB cycles up to the seventh cycle. The results confirmed that the ARB process with subsequent heat treatment is a suitable method for Al-based alloy sheets fabrication with high mechanical properties responses.

Tensile properties optimization of Al/electroplating-Cu composites fabricated by accumulative roll bonding (ARB)

A novel method combing electroplating and ARB was used to manufacture multilayer composites in this research. Pure Cu was electroplated on the Al-1060 and stacked with the Al-1060 sheets alternately; as a result, the multilayer metals were made into composites by ARB. It is indicated that both grains and AlCu intermetallic compounds significantly refined, together with well-bonded interfaces after ARB. Note that the tensile properties improved significantly. By applying 6 cycles of ARB, both the yield stress (YS) and ultimate tensile stress (UTS) were increased by more than 100 MPa and a negligible adverse influence on the elongation was caused. Therefore, it is very promising to apply this strategy of combining electroplating and ARB to produce composites with superior properties.

Effect of Accumulative Roll Bonding (ARB) strain path on microstructural evolution and crystallographic texture development in aluminium

In the present study nine successive ARB cycles were applied on double-layer 1 mm aluminum sheets following three different routes; normal, reverse and cross. Severely deformed sheets were studied by XRD and EBSD to show the evolution of crystallographic textures, while mechanical properties are characterized by micro-tensile and micro-hardness tests. Results indicate that changing the route significantly affects the formation of crystallographic texture components in the structure, leading to different macro mechanical properties. As the asymmetry increases in the strain route, the intensity of the texture components reduces by 57% from as-received structure to the most asymmetric ARBed sample, i.e., cross route. The difference is attributed to different activated slip system in each route. The higher the asymmetry of the route, the lesser the necessity for the cross-slip, and the more the dynamic recrystallization in the structure. Hence, the finest grains happen to form in Normal ARBed sample. The same mechanism is responsible for higher strength (36%) and hardness (32%) observed in Normal ARBed sample. However, the change of route also lowers the bond strength in Cross and Reverse ARBed samples, weakening them by almost 12% regarding the as-received sheet.

Solid-state alloying of Al-Mg alloys by accumulative roll-bonding: Microstructure and properties

In this study, a novel solid-state alloying approach was adopted to fabricate Al-Mg alloys with high Mg contents (CMg) by accumulative roll-bonding (ARB) of Al and Mg elemental materials to ultrahigh cycles. Experimental results showed that the degree of alloying increased with the increase of ARB cycles and a supersaturated α-Al solid solution accompanied with nanoprecipitates was formed in the Al-Mg alloys by ARB to 70 cycles. The as-prepared Al-Mg alloys exhibited enhanced mechanical properties, with a maximum tensile strength of ∼ 615 MPa and a tensile elongation of ∼ 10% at CMg = 13 wt.%. The high strength can be attributed to different mechanisms, namely solid solution strengthening, grain boundary strengthening, dislocation strengthening, and precipitation strengthening. The Al-Mg alloys showed increased work hardening with increasing CMg, due to the enhanced formation of nanoprecipitates. Meanwhile, no obvious drop in the intergranular corrosion (IGC) resistance was found in the Al-Mg alloys with CMg up to 13 wt.%. Moreover, sensitization treatment was found to induce little decrease in the IGC resistance of the Al-Mg alloys with CMg ≤13 wt.%. We found that the excellent IGC resistance was due to the suppression of grain boundary precipitation by the preferred formation of precipitates within the grains that were induced by ARB. Our study indicated the novelty of the present solid-state alloying approach to achieving a superior combination of high mechanical properties and IGC resistance in Al-Mg alloys.

Microstructure and enhanced cryogenic tensile property of a heterostructured Al–AlN/Al–Mg composite fabricated by accumulative roll bonding (ARB)

Recently, heterogeneous structured materials have attracted considerable attention due to their excellent mechanical properties. In this work, a heterostructured Al–AlN/Al–Mg laminated composite was successfully prepared by accumulative roll-bonding (ARB), and the microstructural evolution and tensile properties both at room temperature and under liquid nitrogen temperature were investigated systematically. It is found that the distribution of AlN particles in Al–AlN layer has been optimized to be more uniform to avoid sever stress concentration; both the Al matrix grains in the Al–AlN and Al–Mg layers were refined significantly with the increase of ARB cycles. In addition, the interfaces of Al–AlN and Al–Mg layers were well bonded and kept straight without any necking or fracture after ARB process. Compared with the room temperature tensile properties, the cryogenic tensile strength, yield strength and ductility of the Al–AlN/Al–Mg composite under liquid nitrogen temperature were enhanced simultaneously, which reached to 473.7 MPa, 363.1 MPa and 9.88%, increased by 51.8%, 39.0% and 83.3%, respectively. It is found that the strain hardening rate under liquid nitrogen temperature was also enhanced significantly. It is proposed that the hetero-deformation induced (HDI) stress played a crucial role in the significant enhancement of tensile strength and ductility for the laminated composites.

Wear behavior of laminated nanostructured CP-Ti sheets fabricated by severe plastic deformation

In this investigation, nanostructured titanium sheets were produced by accumulative roll bonding (ARB). A reciprocating tribometer in a pin-on-flat contact configuration was used to evaluate the wear behavior of ARB-processed sheets. The microstructure of materials was characterized using an optical microscope and transmission electron microscope (TEM). The worn surface was studied by a scanning electron microscope (SEM). A peeling test was used to investigate the bonding strength of clad metal sheets. The results showed that the mean grain size of the material reached 110 nm after 8 ARB cycles. For a sliding distance of 1000 m, the wear weight loss decreased by ∼10% up to the fourth ARB cycle and then increased by ∼80% up to the eighth cycle compared to the raw material. Almost identical changes in the wear resistance were observed under different normal loads. The variation in wear resistance was attributed to the work hardening, grain size, and the layered structure of the material.

Microstructure and mechanical properties of Al2O3-particle-reinforced Al-matrix composite sheets produced by accumulative roll bonding (ARB)

Accumulative roll bonding (ARB) was used to fabricate aluminum matrix composites (AMCs) with 2 vol% Al2O3 particles. Monolithic sheets without Al2O3 particles under the same conditions were also fabricated for comparison. For all produced sheets, different variables, such as average grain size, fraction of high angle grain boundaries and local number of 2-dimension at random points (LN2DR), were measured to better understand the evolution of matrix microstructure and particle spatial distribution. The role of Al2O3 particles on strengthening in AMCs processed by ARB was finally revealed. It was found that during ARB, monolithic sheets exhibited deformed-micrometer grains. In comparison, composites also started with deformed-micrometer grains, however, evolved over ARB cycles to have significantly refined grains. Machine learning results showed that particle spatial uniformity improved with the increasing number of ARB cycles. After the 11 cycles of ARB, final composites were more strengthened (1.15 times higher Vickers hardness, 1.19 times higher tensile strength), however, had less elongation than the monolithic sheets. Therefore, comparing to monolithic sheets, the composites are more strengthened not only due to the matrix strain hardening and grain refinement caused by ARB, but also the presence of Al2O3 particles with improved spatial uniformity.

Forming limit diagrams and mechanical properties of AA1050/Ti CP2 multilayered composite produced by the accumulative roll bonding technique

In this study, the AA1050/Ti CP2 metallic multilayered composite was produced by accumulative roll bonding (ARB) using AA 1050 and commercially pure titanium Ti (CP-Ti ASTM grade 2) for three cycles at ambient temperature. The microstructure evolution was investigated by scanning electron microscopy (SEM) equipped with an energy dispersive spectrometer (EDS) and X-ray diffraction (XRD). Also, the tensile test and Vickers microhardness measurement were conducted to evaluate mechanical properties. The forming limit diagrams (FLD) were obtained for a metallic multilayered composite for the first time by the Nakazima test. It was observed that a continuous and well-bonded composite was fabricated after the first cycle. For the subsequent two cycles, necking and fracture of Ti reinforcement occurred in the Al matrix. The maximum tensile strength was reached after two cycles with almost a 98% increase compared to the annealed aluminum sample. However, the tensile strength was reduced after the third cycle. The uniform elongation considerably decreased after the first cycle and was maintained for the subsequent two cycles. The microhardness improved by 124% and 47% for Al and Ti, respectively, in the whole process of ARB in comparison with annealed Al and Ti. As a formability criterion, the level of forming limit curve (FLC) was reduced sharply after the first ARB cycle. For subsequent cycles, this reduction was neglectable. The Al/Ti composite fracture surfaces were a combination of shear ductile and brittle after the third pass.

Effect of Heterogeneous Ti Layers on Mechanical Properties of Cu/Ti Laminated Sheets Prepared by Accumulative Roll Bonding

Cu/Ti laminated sheets with heterogeneous Ti layers are successfully fabricated by accumulative roll bonding (ARB). The microstructure during processing is characterized by scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD). During the deformation of the constituent metals, the hard Ti layers neck preferentially but with a continuous layered structure. Upon four ARB cycles, there are five Ti layers with different microstructure states and grain sizes (from 1.3 to 0.5 μm) in the ARB4 sample. Tensile test of ARB4 sample indicates excellent comprehensive mechanical properties, compared with pure Cu and pure Ti, it has higher ultimate tensile strength (508 MPa), and the elongation (9.2%). In the result of loading–unloading–reloading test, there is a strain gradient during the tensile process due to heterogeneous existence of Ti layers, which produces a multilevel hetero‐deformation‐induced (HDI) stress strengthening and improves the coordinated deformation ability of the sample. Second, layered structure and interface with alternate strong and weak bonding can effectively hinder the propagation of cracks to outline higher strength with improved ductility. This structural design helps to prepare laminated materials sheet with excellent comprehensive mechanical properties through the ARB process.

Surface morphology and Rietveld refinement characterisation of aluminium/titania nanocomposite produced by atmospheric plasma spraying and accumulative roll bonding

ABSTRACT In this study, the nano-sized Titania (TiO2) particles were coated on an aluminum (Al) matrix using the atmosphere spraying method, and then the Al-TiO2 nanocomposite was fabricated by the accumulative roll bonding (ARB) process. The surface morphology evaluation by the field emission scanning electron microscopy (FESEM) revealed that TiO2 nanoparticles are uniformly spread and the amount of TiO2 nanoparticles decreased on the surface during the ARB process energy dispersive spectroscopy (EDS) mapping and X-ray diffraction (XRD) analysis demonstrated a decrease in the TiO2 phase while an increase in the Al phase in further cycles of the ARB process. Based on the atomic force microscopy (AFM) micrograph, the thicknesses of TiO2 particle clusters decreased from 1.26 μm to 238 nm by increasing the number of ARB cycles. The surface roughness values measured by the profilometer showed that the pressure of rolling has been an effect on reducing roughness to 96 micrometers, up to seven cycles of the ARB process. to calculate the Al crystallite size, TiO2 nanoparticles size, micro-strains and dislocation densities, the Rietveld refinement indicated that the increasing micro-strains and dislocation densities have led to reducing the Al crystallites and TiO2 particle clusters size to 234 and 40 nm, respectively.

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.

Shear banding-induced 〈c+a〉 slip enables unprecedented strength-ductility combination of laminated metallic composites

Shear bands in metallic materials have been reported to be catastrophic because they normally lead to non-uniform plastic deformation. Ductility of laminated metallic composites deteriorates with increasing processing strain, particularly for those having hexagonal-close-packed (hcp) constituents due to inadequate slip systems and consequently prominent shear banding. Here, we propose a design strategy that counterintuitively tolerates the bands with localized strains, i.e. the shear banded laminar (SBL) structure, which promotes 〈c+a〉 dislocation activation in hcp metals and renders unprecedented strength-ductility combination in hcp-metal-based composites fabricated by accumulative roll bonding (ARB). The SBL structure is characterized with one soft hcp metal constrained by adjacent hard metal in which dislocations have been accumulated near the bimetal interfaces. High-energy X-ray diffraction astonishingly reveals that more than 90% of dislocations are non-basal in Ti layers of the SBL Ti/Nb composite processed by eight ARB cycles. Moreover, 〈c+a〉 dislocations occupy a high fraction of ∼30%, promoting further 〈c+a〉 cross slip. The unique stress field tailored by both shear banding and heterophase interface-mediated deformation accommodation triggers important 〈c+a〉 slip. This SBL design is of significance for developing hcp-based laminates and other heterostructured materials with high performances.

Investigation of the joinability of single- and multi-layered AA6014 sheets produced by accumulative roll bonding in the shear-clinching process

Accumulative roll bonding belongs to the severe plastic deformation processes and is suitable for producing multi-layered as well as high-strength sheets through repeated rolling. After four accumulative roll bonding-cycles, the strength of the investigated AA6014-T4 alloy is elevated due to strain and fine grain hardening by 170% in yield strength and by 37% in ultimate tensile strength. This is accompanied by a significant decrease in material ductility which is disadvantageous for joining processes based on forming operations. Shear-clinching, however, can be used to join high-strength and low-ductile materials on the die side. Thus, it is a promising method for the mechanical joining of accumulative roll bonding components. The multi-layered and more brittle material is located on the die side whereas the single-layered base material with higher ductility is positioned on the punch side. At present, there is no scientific knowledge how the multi-layered material behaves in the shear-clinching process. Since the material is cut in the process, delamination effects could occur at the interfaces produced via accumulative roll bonding. Additionally, the investigation aims at the influence of the accumulative roll bonding process on the properties of the joints. They are expected to depend on the number of process cycles and thus on the change of mechanical properties of the multi-layered material. The bond strength of the shear-clinched joints is determined by shear and tensile tests. The areas of material failure are analysed via metallographic methods. From the failure behaviour and load-bearing capacity it is determined which number of accumulative roll bonding cycles is ideal for joining multi-layered sheets via shear-clinching.

Abnormal texture evolution of accumulative roll bonded Al–Cu by adding alumina particles

Evolution of the texture of an Al–Cu composite after addition of alumina particles was investigated in details using X-Ray Diffraction (XRD) method. Composite samples were produced by the Accumulative Roll Bonding (ARB) and alumina particles were uniformly added to the composite using anodizing technique. The process was accompanied by cutting, stacking and rolling the lamellar materials up to seven times. In early stage of ARB, a shear texture close to the Rotated Cube formed for the Al side. This texture development was also confirmed by microstructural investigation on shear bands during deformation employing optical and scanning electron microscopy. In the last two cycles, a nearly random orientation of grains was developed. For the Cu side, however, the recrystallized Cube texture component was prominent for early ARB cycles due to the recrystallization phenomenon. Moreover, a mixture of rolling and recrystallized texture was detected for the Cu side at higher ARB cycles. Furthermore, evaluation of the grain boundaries showed an increase in the number of high angle grain boundaries for the final ARB cycles in both Al and Cu sides, confirming the occurrence of grain refinement during ARB. Localized particle deformation zone (PDZ) around alumina particles was also proposed to have a contribution to textural evolution of the composite.

Microstructure and tensile behavior of high-chromium cast iron/low-carbon steel composite fabricated by accumulative roll-bonding

In the present study, a composite material of high chromium cast iron (HCCI) dispersed in low carbon steel (LCS) matrix was fabricated by the technology of accumulative roll-bonding (ARB). The microstructure characteristics were investigated using scanning electron microscopy (SEM) and electron back-scattered diffraction (EBSD). The tensile behavior and fracture characteristics of the composite were analyzed. The obtained microstructures illustrated that the HCCI was dispersed in the LCS after 3rd ARB cycle, forming a kind of composite material somewhat similar in its structure to a concrete. The coarse Cr-carbides of HCCI were broken and refined obviously through the hot-rolling deformation. However, some microcracks were formed on the fractured Cr-carbides of HCCI. The two materials were bonded by mechanical and metallurgical bonding, and a diffusion band with a thickness of ∼10 µm was formed on the interface. Compared with the as-cast HCCI plate, the composite material after 3rd ARB cycle possessed good comprehensive tensile properties. The fracture characteristics of the composite material included the multiple tunnel fracture of HCCI and the shear fracture of LCS.

Microstructure and properties analysis of accumulative-roll-bonding-processed Mg–Li/Ta composites for shielding of high-energy electron

The rational combinations of low/high-density metallic materials have been proved to be effective in shielding high-energy electron radiation, however, little has been studied and reported about their synthesis, microstructure, properties and stability against irradiation. In present work, Mg–Li alloy and pure Ta sheets were used to prepare such a novel low/high-density shielding composite by accumulative roll bonding (ARB). Results showed that a uniformed microstructure of composite could be produced after four ARB cycles. Both ARB process and irradiation caused no obvious change in phase compositions of raw materials. In larger areal mass 8.2–12.3 g/cm2, the Mg–Li/Ta composite is a more efficient shield than pure Mg–Li and Ta. Treated by irradiation, a notable number of cavities accompanied by dislocations were formed as main defects in α-Mg phase. The induced dislocations facilitated the nucleation and growth of {1 0–1 2} twins, which in turn acted as sinks of defects. By contrast, Ta phase exhibited good radiation stability as no signs of visible cavities. During ARB process and irradiation, the textures of α-Mg and Ta in composite all varied distinctly. The average micro-hardness of Mg–Li and Ta phase increased with ARB cycles. Treated by irradiation, Mg–Li matrix was sharply hardened while hardness of Ta was slightly decreased. The tensile strength of Mg–Li/Ta composite increased in ARB process and reached the maximum after four cycles. After irradiation, composite exhibited same strength but severe loss of ductility.

Microstructure and mechanical behaviors of Al/Cu laminated composites fabricated by accumulative roll bonding and intermediate annealing

Strength and toughness of laminated composites with alternatively stacked “brick-and-mortar” structure can be synchronously improved along the direction parallel to the layer interface. However, it is still a challenge to prepare high-performance laminated composites in large quantities to meet industrial needs. In this work, we employ accumulative roll bonding (ARB) and/or intermediate annealing to prepare Al/Cu laminated composites as cheaper substitutes for Cu alloys due to lightweight and considered electrical conductivity. Our results show that the ARB process decreases the layer thicknesses and grain sizes, and improves the Vickers micro-hardness of Al/Cu laminated composites. As the ARB cycle increases from 1 to 8, the tensile strength firstly increases from 279.20 MPa to 358.71 MPa, and then decreases to 317.88 MPa. Meanwhile, the uniform elongation firstly increases from 1.25% to 1.71%, and then decreases to 0.58%. These variations of tensile properties are tightly linked to the layer-integrity and microstructures of Al and Cu layers. Moreover, the intermediate annealing (350 °C for 30 min) applied after every 2 ARB cycles can significantly increase the tensile strength, uniform elongation and elongation to failure, especially for Al/Cu laminated composites with high ARB cycles, because intermediate annealing remarkably improves the interfacial metallurgical bonding and continuity/integrity of Al and Cu layers. However, the final annealing for long time would introduce brittle intermetallics (like AlCu and Al2Cu), and therefore deteriorate the tensile ductility. This work provides a new treatment process for fabricating Al/Cu laminated composites with synchronously increasing strength and ductility.

Microstructure and mechanical properties of Mg-14Li-1Al/MWCNTs composites prepared by electrophoretic deposition and accumulative roll bonding

Mg-14Li-1Al/MWCNTs composites were prepared by electrophoretic deposition and accumulative roll bonding (ARB). The mechanical properties and microstructure was characterized by tensile test, microhardness, optical microscope and transmission electron microscope. After 6 cycles of ARB, the yield strength, ultimate tensile strength and elongation of the composite are 213 MPa, 266 MPa and 21.6%, respectively. Compared with the as-cast alloy and as-rolled alloy, the yield strength and ultimate tensile strength of the composite were increased by 142.04% and 82.05%, 79.72% and 60.24%, respectively. A highest specific strength of 189 kNm/kg was obtained. The highest microhardness value of the composite is 84.6 HV, which is 66.86% and 49.73% higher than that of the as-cast (50.7 HV) and as-rolled (56.5 HV) alloys. High density dislocations, ultrafine grains, and carbon nanotubes with uniform dispersion were observed in the Mg-14Li-1Al/MWCNTs composites. The strengthening of the composites is mainly contributed to fine grain strengthening and dislocation strengthening.