Accumulative Roll Bonding Process Research Articles

Ultrafine grained copper alloy sheets having both high strength and high electric conductivity

The ultrafine grained (UFG) microstructure, mechanical properties and electric conductivity of the Cu alloys severely deformed by accumulative roll bonding (ARB) process were systematically investigated. High density of grain boundaries introduced by the ARB process has significant effect on strengthening but little effect on the electric conductivity. The UFG Cu alloys with submicometer grain sizes can achieve both superior mechanical properties and high electric conductivity.

Role of second phase particles on microstructure and texture evolution of ARB processed aluminium sheets

The accumulative roll bonding (ARB) process was carried out on a high purity alloy (AA1100) and a particle containing aluminium alloy (AA3003) for up to eight cycles. The electron backscattered diffraction (EBSD) method was utilised to investigate the microstructural and microtextural evolution in ARB processed sheets. The results indicate that the lack of second phase particles in pure aluminium hinders grain refinement and leads to the formation of unrefined bands, which results in the increase of the overall texture intensity and the development of a strong texture. A submicrometre grain structure in this alloy develops at the final stages of the process. It was also found that the presence of second phase particles in AA3003 alloy prevents the development of such unrefined bands and improves grain refinement during the ARB process, which results in a more homogenous microstructure of ultrafine grains.

Quantification of strain in accumulative roll-bonding under unlubricated condition by finite element analysis

The each strain component and equivalent strain in rolled materials were quantified using finite element analysis (FEA) that takes the deformation history into account. FE simulations were carried out considering stress–strain relations that depend on strain rate and friction between rolls and sheet. Rolling condition of accumulative roll-bonding (ARB) where introduction of a very large shear strain in the surface layer of rolled sheet had been verified through the embedded-pin method was employed in FEA. The histories of total shear strain, total strain in rolling direction, and equivalent strain during rolling were studied, and the magnitude and distribution of each of them through sheet thickness after rolling were shown. The problems associated with the experimental determination from an embedded-pin method were clarified through the present analysis. The equivalent strain at the surface in the 1100 Al processed by one ARB cycle without lubricant corresponded to the equivalent strain in the material processed by five ARB cycles with lubricant. These quantitative strain analyses would be useful for analyzing the evolution of microstructures in the ARB process as well as the conventional rolling deformation under high friction conditions.

Metallurgical aspects on the formation of self-organized anodic oxide nanotube layers

The present work reports how metallurgical factors such as grain size and chemical composition of substrate affect the current behavior during anodization and the morphology of resulting formed oxide layers. The grain size of pure Ti sheet is controlled by the accumulative roll-bonding (ARB) process. Tubular oxide layers are formed on the ARB-processed Ti sheets with different grain sizes, but grain size does not affect the length, diameter of tubes and the degree of tube arrangement. The effect of chemical composition is examined using Ti–Zr alloys (Ti–20Zr, Ti–50Zr, Ti–80Zr) that can consist of a single phase, meaning that homogeneous tube formation can be achieved. With increasing Zr content in the alloys, tube diameter decreases while tube length increases. For the Ti–50Zr and Ti–80Zr, self-organization is achieved on two size scales, that is, nanotube arrays with two distinct diameters are observed. TEM observation revealed that anodic oxide layers are in crystalline state only in the case of pure Zr.

High-strength, high-conductivity ultra-fine grains commercial pure copper produced by ARB process

Accumulative roll-bonding process is a severe plastic deformation process capable of developing grains below 1 μm in diameter. In this study, microstructure, mechanical properties and electrical conductivity of commercial pure copper strips processed by accumulative roll-bonding were investigated. Transmission electron microscopic micrographs of the strips produced by eight cycles of accumulative roll-bonding process showed ultra-fine grains ∼180 nm in size with high angle grain boundaries. Also tensile strength and microhardness of the accumulative roll-bonding processed samples increased with increasing the number of accumulative roll-bonding cycles. Whereas, the elongation dropped abruptly at the first cycles, above which it increased slightly. The electrical conductivity decreased with increasing accumulative roll-bonding cycles up to 6 cycles and then increased up to 8 cycles of accumulative roll-bonding process.

Significant enhancement of bond strength in the accumulative roll bonding process using nano-sized SiO 2 particles

Accumulative roll bonding (ARB) is one of the most promising methods for the industrial production of ultrafine grained (UFG) sheet materials. The poor bond strength is one of the major drawbacks in the ARB process. Degreasing and wire-brushing have been widely adopted in ARB to improve bonding. In this paper, the nano-sized SiO 2 particles has been used to enhance the bond strength. The bond strength in our samples exceeds 2.5 times the values achieved by degreasing and wire-brushing methods. In addition, the mechanical properties and microstructures of the ARB-processed samples have also been investigated.

Brittle-Ductile Transition in Low Carbon Steel Deformed by the Accumulative Roll Bonding Process

Brittle-ductile transition (BDT) behaviour was investigated in low carbon steel deformed by an accumulative roll-bonding (ARB) process. The temperature dependence of its fracture toughness was measured by conducting four-point bending tests at various temperatures and strain rates. The fracture toughness increased while the BDT temperature decreased in the specimens deformed by the ARB process. Arrhenius plots between the BDT temperatures and the strain rates indicated that the activation energy for the BDT did not change due to the deformation with the ARB process. It was deduced that the decrease in the BDT temperature by grain refining was not due to the increase in the dislocation mobility controlled by short-range obstacles. Molecular dynamics simulations revealed that moving dislocations were impinged against grain boundaries, creating a shielding field, and were reemitted from there with increasing strain. Grain refining led to an increase in the fracture toughness at low temperatures and a decrease in the BDT temperature. In the present paper, the roles of grain boundaries have been discussed in order to explain the enhancement in the fracture toughness of fine-grained materials at low temperatures, and the decrease in the BDT temperature.

Increasing the ductility of ultrafine-grained copper alloy by introducing fine precipitates

We fabricated ultrafine-grained (UFG) Cu–Cr–Zr alloy including fine second-phase particles via an accumulative roll-bonding process and subsequent aging treatment. The nanosized precipitates dispersed within the UFG matrix significantly enhanced strain hardening, resulting in the simultaneous improvement of uniform elongation and tensile strength.

Effect of strain on “hardening by annealing and softening by deformation” phenomena in ultra-fine grained aluminum

Ultra-fine grained (UFG) metals fabricated by severe plastic deformation (SPD) sometimes exhibit peculiar mechanical properties. For example, the “hardening by annealing and softening by deformation” was reported in UFG aluminum, which was totally opposite to the behaviors of conventionally coarse-grained materials. In this study, the effect of SPD strain on the peculiar phenomena was investigated. The UFG aluminum was fabricated by various cycles of the accumulative roll-bonding (ARB) process with lubrication at ambient temperature. The specimen ARB-processed by ten cycles certainly showed the peculiar phenomena. On the other hand, the 6-cycle specimen did not show the phenomena but was softened by annealing and hardened by deformation normally. From the results of microstructural characterization, it was suggested that the difference in the change of the mechanical property during annealing and deformation between 6-cycle and 10-cycle specimens was caused by the difference in the grain size and/or the texture components, which depended on the SPD strain.

Microstructural evolution and mechanical properties of accumulative roll bonded interstitial free steel

Severe deformation processing is an emerging technique, for the production of submicron grain structures in metallic material, which involves plastic deformation to ultra-high strains. An ultra-fine grained (UFG) material was prepared from an IF steel sheet using Accumulative Roll Bonding (ARB) process. After initial preparing to achieve good sheet bonding, ten cycles of ARB at 500 °C were successfully performed. Atomic Force Microscopy (AFM) and Transmission Electron Microscopy (TEM) were used for the characterization of subgrain and grain structures of ARB processed samples. The mechanical attributes after rolling and cooling were examined. Also, the fracture surfaces were studied by Scanning Electron Microscopy (SEM). It was concluded that metal’s tensile strengths increased by 334% while the ductility dropped from a pre-rolled value of 50.5% to 2.6%. The rolling process was stopped in cycle 10, when cracking of the edges became pronounced.

Microstructure and mechanical properties of ultra-fine grains (UFGs) aluminum strips produced by ARB process

Accumulative roll-bonding (ARB) process is a severe plastic deformation process capable of developing grains below 1 μm in diameter and to improve mechanical properties. In this study, strips of a commercial pure aluminum were ARB-processed to eight cycles, and their microstructures and mechanical properties were investigated. XRD and TEM studies of the strips showed grain refinement, and the TEM micrograph of the alloy ARBed for eight cycles showed ultra-fine grains (UFGs) of high-angle grain boundaries ∼360 nm in size. The ambient tensile strength and microhardness of the ARB-processed samples increased with the number of ARB cycles. Whereas, the elongation dropped abruptly at the first cycles, above which it remained nearly constant. With increasing ARB process, the bending strength increased and sliding wear resistance decreased. SEM fractography of fractured surfaces after tensile tests revealed that failure mode in ARB-processed aluminum was shear ductile rupture with elongated small dimples.

Microstructure evolution upon annealing of accumulative roll bonding (ARB) 1100 Al sheet materials: evolution of interface microstructures

The microstructure evolution upon annealing of 1100 aluminum samples that were accumulative roll bonding (ARB) processed were studied with the use of transmission electron microscopy. It was found that the ultra-fine microstructure resulted from the ARB process was not stable. Specifically, a two-stage grain growth behavior was observed, in which a relatively slower rate of grain growth was followed by a more rapid grain growth rate at higher annealing temperature. The bonding interfaces that were unique to the roll bonding process were found to have a significant influence on the grain growth behavior when the grain size of the material was of similar dimension as the bonding interface separation. Discontinuous pockets consisting of smaller grains were found to have formed upon annealing. These pockets represented the remnants of the heavily deformed layer from wire brushing.

WEAR PROPERTIES OF 1100 AL ALLOY PRODUCED BY ACCUMULATIVE ROLL BONDING

Ultra-fine grained 1100 Al alloy was successfully produced by accumulative roll bonding (ARB) process. TEM investigation and SAD patterns showed that, after eight cycles of ARB, sheets were found to contain ultra-fine grains with high angle grain boundaries. The mechanical properties of the ARB processed (ARBed) 1100 aluminum alloy increased with increasing the number of ARB cycles. The elongation dropped abruptly at the first cycles. Wear properties were investigated using a pin on disk wear machine at ambient environment. Contrary to an expectation, the wear resistance of the ARBed Al alloy was less than the non-processed Al alloy. Morphologies of worn surfaces were studied by scanning electron microscope (SEM).

THE EFFECTS OF ACCUMULATIVE ROLL BONDING PROCESS ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF IF STEEL

This work aims to investigate whether accumulative roll bonding (ARB) is an effective grain refinement technique for ultra-low-carbon steel strips containing 0.004% C. For this purpose, a number of ARB processes were performed at 500 °C, with 50% reduction in area of each rolling pass. It was found that both the ultimate grain size achieved, as well as the degree of bonding, depend on number of rolling pass and reduction of area as a whole. The mean grain size was obtained using AFM was about 130nm. The mechanical properties after rolling and cooling were obtained. Also, the fracture surfaces were studied by Scanning Electron Microscopy (SEM). It was concluded that metal's tensile strengths increased by 334% while the ductility dropped from a prerolled value of 50.5% to 2.6%. Effect of wire brushing on samples observed too. It increased on the wire brushed sheet for 7 HV. The rolling process was stopped when cracking of the edges became pronounced.

Microstructure evolution and mechanical properties of AA1100 aluminum sheet processed by accumulative roll bonding

In this study, accumulative roll bonding (ARB) process was carried out on an AA1100 aluminum sheet up to 10 cycles. Electron backscattering diffraction (EBSD) method was utilized to investigate the microstructural evolution during the ARB process. It was observed that the ARB is a promising process for fabricating ultra-fine grained structures in aluminum sheets. The results indicate that several mechanisms are responsible for the microstructural changes at different levels of strain during this process. Grain subdivision as well as the development of sub-grains are the major mechanisms at the early stages of ARB. Strain induced transition of low angle to high angle grain boundaries and the formation of thin lamellar structure occurs at the medium levels of strain. Finally, the progressive break up of this thin lamellar structure into more equiaxed grains is the dominant mechanism at relatively high strains. By reducing the grain size, the yield stress and the tensile strength of the ARBed sheets increased significantly and reached the maximum values of 282 and 333 MPa after the tenth cycle. The strength held Hall–Petch relationship and was in a good conformity with the microstructural changes.

Microstructure and Aging Behavior of Al-0.2wt%Zr Alloy Heavily Deformed by ARB Process

An Al-0.2wt%Zr alloy was severely deformed up to a strain of 8.0 by accumulative roll bonding (ARB) process, started from the solution-treated state. The microstructural evolution during ARB and its aging behavior were investigated. With increasing the number of ARB cycles, Vickers hardness of the specimens increased and reached to a constant value. The microstructural evolution during the ARB could be understood in terms of grain subdivision. The ultrafine grained (UFG) materials whose mean grain size was 0.4 -m were obtained by 10-cycle ARB process. In aging of the ARB processed specimens at high temperatures above 673K, the UFG microstructures quickly coarsened. On the other hand, it was suggested that the precipitation behaviors of the ARB specimen at 623K were quite unique and completely different from those of the conventionally solution-treated material with coarse grain size.

Fracture Toughness Enhanced by Severe Plastic Deformation in Low Carbon Steel

The enhancement of toughness at low temperatures in fine-grained low carbon steel was studied, basing on the theory of crack-tip shielding due to dislocations. Low carbon steel was subjected to an accumulative roll bonding (ARB) process for grain refining. The grain size perpendicular to the normal direction was decreased to approximately 200nm after the ARB process. The fracture toughness of low carbon steel with the ARB process was measured at 77K by four-point bending, comparing with the fracture toughness of those without the ARB. It was found that the value of fracture toughness at 77K was increased by grain refining due to the ARB process, indicating that the ARB process enhances toughness at low temperatures and that the brittle-to-ductile transition (BDT) temperature shifted to a lower temperature. Quasi-two-dimensional simulations of dislocation dynamics, taking into account crack tip shielding due to dislocations, were performed to investigate the effect of a dislocation source spacing along a crack front on the BDT. The simulation indicates that the BDT temperature is decreased by decreasing the dislocation source spacing.

Microstructure and Mechanical Properties of Al-0.5 at.% X (=Si, Ag, Mg) Alloys Highly Deformed by ARB Process

Effect of solid solution elements on microstructure evolution and mechanical properties was investigated using a high purity Al (purity 99.99%) and Al-0.5 at.% X ( X = Si, Ag, Mg ) alloys deformed by accumulative roll bonding (ARB) process up to 7 cycles (equivalent strain of 5.6) at ambient temperature. The ARB-processed high purity Al showed the equiaxed microstructure having mean grain size of 750 nm. On the other hand, the microstructure of the ARB-processed Al-0.5at.%X alloys showed lamellar boundary structures elongated along RD. The mean lamellar boundary spacing significantly differed depending on the alloying elements, which suggested that solute atoms had a significant effect on microstructure evolution. The difference in the grain size was regarded to be caused by the difference in recovery processes in the alloys. The tensile strength of the alloys increased with increasing the number of ARB cycles. In the Al-Si and Al-Ag alloys, the post-uniform elongation increased with increasing the number of the ARB cycles. On the other hand, the elongation of the Al-Mg hardly changed during the ARB process.

Structure and Mechanical Properties of Severely Deformed Cu-Cr-Zr Alloys Produced by Accumulative Roll-Bonding Process

Aging behavior and mechanical properties of ultra fine grained Cu-Cr-Zr alloy sheet produced by accumulative roll bonding (ARB) process were investigated. A Cu-0.85Cr-0.07Zr (in mass%) alloy was solution treated and then cold-rolled at ambient temperature in the sheet of 1 mm thick. The sheets were heavily deformed by ARB process at ambient temperature up to 5 cycles. The grain size was reduced down to 210 nm and the fraction of high angle grain boundaries (HAGB’s) in the specimen after ARB process was 63%. The proof stress ( σ 0.2) and elongation were 540 MPa and 10%, respectively. Due to the aging treatment, a little grain growth took place (240 nm) and the fraction of HAGB’s was increased to 67%. The proof stress and elongation of the aged one increased to 605 MPa and 15%, respectively. It was noteworthy that the electrical conductivity remarkably increased from 35% to 79%IACS by the aging treatment. It was concluded that the aging treatment after ARB process enhanced not only the mechanical properties but also the electrical conductivity in the Cu-Cr-Zr alloys.

Effect of Strain Rate on Microstructural Evolution of Nano-Grained Copper in Accumulative Roll-Bonding Process

The effects of strain rate in rolling on microstructures and mechanical properties of a nano-grained high purity copper processed by accumulative roll bonding (ARB) were studied. The rolling during ARB was conducted with two kinds of strain rates (2.6sec-1 and 37sec-1). The microstructural evolution of the copper with ARB proceeding was somewhat different in both methods. However, the variation of mechanical properties with ARB was very similar to each other.