Papers by Keyword: Accumulative Roll Bonding (ARB)

Abstract: An interstitial-free steel was severely plastically deformed in an accumulative roll bonding (ARB) experiment with 10 consecutive passes applied at 480°C. Nominal reductions of 50% per pass and an intermediate annealing treatment of 5 min. at 520°C were employed. A total true strain of evM = 8.00 was applied, which corresponds to an accumulated reduction of 99.9%. The evolution of texture and microstructure was monitored by means of orientation imaging microscopy. A lamellar microstructure, characteristic of severely rolled sheet materials, was observed even after the highest strains. The average lamellar width was determined as a function of rolling strain. Under the experimental limitations in terms of spatial resolution, no significant difference was observed between the average lamellar width in the mid-section and near the surface of the sheet. Texture analysis revealed a conventional cross-sectional gradient with plane strain rolling components in the mid-layers and shear components in the subsurface regions. Although these different strain modes did not affect the microstructure in terms of the average lamellar spacing, an effect was observed on the average aspect ratio of the grains. This was much higher in the sheared (surface) layers than in the plane strain compressed (centre) areas. The surface structure did not have an effect, though, on the bulk microstructural evolution in spite of the specific nature of the ARB process during which the surface layer of one pass reappears in the mid-section of the next pass.

Abstract: The mechanical behavior of nano grain-sized pure copper produced by various SPD (severe plastic deformation) processes such as ECAP (equal channel angular pressing) and ARB (accumulated roll bonding) was investigated in relation to the microstructural evolution. These processes promoted the formation of equiaxed nanoscale grains in pure copper. The present observation suggested that the tensile behavior of the specimens prepared by the current SPD processes was influenced by several mechanisms involving strain hardening and dynamic recovery. The heat flow was measured by using a DSC (differential scanning calorimeter) to elucidate the relationship between the dislocation density and the tensile behavior in the specimens.

Abstract: A new application of superplasticity was proposed in the manufacturing process of metal foams. Preform sheets were manufactured using superplastic 5083 aluminum alloy sheets through accumulative roll-bonding (ARB) process. Microcellular aluminum foam plates with 50% porosity were produced through solid-state foaming under the superplastic condition. The cell shape was oblate spheroid, which is effective to reduce the thermal conductivity. The present aluminum foam plates have a potential as an excellent heat insulator.

Abstract: Coarse grains of commercial 5052 Al and 5083 Al alloys were refined by the accumulative roll bonding (ARB) process. Average grain size of the refined microstructure was 200 nm. The 5083 Al alloy that has higher Mg content required more deformation for the refinement. Dry sliding wear behavior of the ultra-fine grained (UFG) Al alloys was investigated using a pin-on-disk wear tester at room temperature. The UFG microstructure of the processed alloys hardly increased the wear resistance of the Al alloys in spite of the increased strength and hardness. Wear rate of the UFG Al alloys was higher than that of the non processed coarse-grained starting alloys. The SEM observation of worn surfaces revealed that surface deformation controlled the wear. The low wear resistance of the UFG Al alloys was attributed to non-equilibrium and unstable grain boundaries and low strain hardening capability of the alloys.

Abstract: Dry-sliding-wear behavior of ultra-fine grained 6061 Al alloy and AZ61 Mg alloy was investigated. The accumulative roll bonding (ARB) and the equal channel angular pressing (ECAP) processes were employed to obtain refined microstructures in the Al and Mg alloys, respectively. Pin-on-disk wear tests of the processed alloys were carried out with various applied load against a 304 stainless steel counterpart. In spite of the increased hardness and strength, wear resistance of the ultra-fine grained 6061 Al alloy was lower than that of the coarse-grained starting alloy. The strength and wear resistance of the ECAP processed AZ61 Mg alloy did not change appreciably despite the refined microstructure. Recrystallization was found to occur during the ECAP process of the Mg alloy. Worn surfaces and cross-sections of the wear-tested specimens were examined to investigate the wear mechanism of the ultra-fine grained Al and Mg alloys.

Abstract: The ARB process has been carried out up to seven cycles on a commercial purity 1100 aluminum alloy to obtain ultra-fine grains with the average grain size of 500 nm. Microstructural evolution of the ARB processed aluminum alloy was examined by a transmission electron microscopy as a function of accumulated total strain. Mechanical properties including hardness, tensile property, and sliding wear characteristics of the severely deformed Al alloy were also investigated. Grain boundaries of the ARB processed alloy were diffusive and poorly defined after the initial ARB cycles, however they changed to well-defined high angle boundaries with the increase of the accumulated strain. Though hardness and strength of the ARB processed alloy were enhanced significantly, wear resistance of the processed alloy hardly increased. The mechanical properties were discussed in connection with the microstructure.

Abstract: Two and six-layer stack accumulative roll bonding (ARB) processes were applied to commercial purity aluminum in order to investigate the effect of the stacking layer number on the mechanical properties. The initial thickness of the aluminum sheets for two and six-layer stack ARB was 1mm and 0.5mm, respectively. Two-layer stack ARB was performed by 50% reduction per cycle. For six-layer stack ARB, the six aluminum sheets were first stacked together and cold-roll-bonded by 50% reduction rolling, and then followed by four-pass rolling so that the final thickness was 0.5mm. The sheet was then cut to the six pieces of same length and the same procedure was repeated to the sheets. The tensile strength of the ARB processed specimens increases with the number of ARB cycles in both two and six layer stack ARB. The tensile strength is lower by the six-layer stack ARB than that by the two-layer stack ARB. The elongation slightly decreases with the number of the ARB cycles, regardless of the stacking layer number. TEM observation reveals that the grain size of the six-layer stack ARB is larger than that of the two-layer stack ARB. The effects of the number of the layers in stacking are explained by the redundant shear deformation.