Investigation of ultrafine grained AA1050 fabricated by accumulative roll bonding

Abstract

Accumulative roll bonding (ARB) is an effective method to produce ultrafine-grained (UFG) sheet materials with high strength. In this work, fully annealed AA1050 sheet with an initial thickness of 1.5. mm was processed by ARB up to five cycles. The microstructure was examined by optical microscopy (OM) and transmission electron microscopy (TEM). The results revealed that ARB is a promising process for fabricating ultrafine grained structures in aluminium sheets and the average grain size after 5-cycle ARB reached approximately 300. nm. Meanwhile, a remarkable enhancement in the strength was achieved and the value was about three times the strength of starting material. The microstructure at the bond interface introduced during ARB was investigated and its influence was discussed in detail. In addition, the microstructure and mechanical properties after ARB were compared with that after deformation by equal channel angular pressing (ECAP) up to the same strain. It has been found that ARB is more efficient in grain refinement and strengthening, which can be attributed to the different deformation modes of the two techniques. Accumulative roll bonding (ARB) is an effective method to produce ultrafine-grained (UFG) sheet materials with high strength. In this work, fully annealed AA1050 sheet with an initial thickness of 1.5 mm was processed by ARB up to five cycles. The microstructure was examined by optical microscopy (OM) and transmission electron microscopy (TEM). The results revealed that ARB is a promising process for fabricating ultrafine grained structures in aluminium sheets and the average grain size after 5-cycle ARB reached approximately 300 nm. Meanwhile, a remarkable enhancement in the strength was achieved and the value was about three times the strength of starting material. The microstructure at the bond interface introduced during ARB was investigated and its influence was discussed in detail. In addition, the microstructure and mechanical properties after ARB were compared with that after deformation by equal channel angular pressing (ECAP) up to the same strain. It has been found that ARB is more efficient in grain refinement and strengthening, which can be attributed to the different deformation modes of the two techniques.

The influence of multiscale heterogeneity on recrystallization in nickel processed by accumulative roll bonding

“…the difference between the core and interface regions) are associated with the entire ARB process, where roll-bonding in each new cycle creates a new center layer with a new interface along two former surfaces. These interfaces contain coarse particles, which are morphologically similar in several ARBprocessed materials [14][15][16][17]. In contrast to previous publications [14][15][16][17], where such coarse particles were either disregarded or described as oxide particles, the EDS analysis conducted in the present work provides clear evidence that these are steel particles.…”

“…The origin of various heterogeneities of deformation texture and deformed microstructure in ARBprocessed materials has been discussed in a number of previous publications [4][5][6][7][8][9][10][11][12][13][14]. Based on these publications, it can be summarized that sample-scale heterogeneities generally reflect the heterogeneous distribution of strain for the last few ARB cycles, whereas microscopic heterogeneities (i.e.…”

“…For example, the average boundary spacing measured along the normal direction (ND) in ARB-processed nickel after a von Mises strain ε vM of 6.4 is ~0.1 µm and the fraction of HABs is ~60 % [3]. There are, however, significant through-thickness heterogeneities both in texture [4][5][6][7][8][9][10] and in the deformed microstructure [9][10][11][12][13][14] after ARB. The latter has been observed both at the microscopic scale and at the sample scale.…”

“…At the microscopic scale, microstructural heterogeneities are present within each individual bonding layer in the form of atypically fine subgrains found in the near-interface regions [10][11][12][13][14] and coarse particles present only along the bonding interface [14][15][16][17]. At the sample scale, microstructural heterogeneities have been described in terms of high misorientation regions (HMRs) and low misorientation regions (LMRs) found in different proportions in subsurface, intermediate and center layers of the ARB stack [9].…”

AccumEx - A New SPD Technique for Fabricating Lamellar Materials

“…However, the elongation after 1 and 2 passes has been observed to be exceptionally good compared to the ARB processed materials [12]. The reducing elongation can be attributed to the saturated strain hardening.…”