Accumulative roll-bonding: first experience with a twin-roll cast AA8006 alloy

doi:10.1016/j.jallcom.2003.10.082

Journal of Alloys and Compounds

Volume 378, Issues 1–2, 22 September 2004, Pages 322-325

https://doi.org/10.1016/j.jallcom.2003.10.082 Get rights and content

Abstract

An ultra-fine grained (UFG) material was prepared from a twin-roll cast (TRC) Al–Fe–Mn–Si (AA8006) sheet using accumulative roll-bonding (ARB) process. After initial failures to achieve good sheet bonding, five cycles of ARB at 200 °C were successfully performed. Scanning electron microscopy (Electron Backscatter Diffraction) and transmission electron microscopy (TEM) were used for the characterization of subgrain and grain structures of ARB processed samples. The strength of ARB sheets was evaluated by microhardness measurements. Very fine grain structure (0.4–0.8 μm) with large disorientation was observed after two cycles of ARB. In two samples, areas with extremely fine grains 0.1–0.3 μm in diameter were found. The hardness of the alloy increased from 28 to 60 HV1 after the first two cycles, but during subsequent ARB processing it rose only very slightly.

Introduction

The accumulative roll-bonding (ARB) is a relatively new method of severe plastic deformation proposed by Saito et al. [1]. The basic goal of ARB is to impose an extremely high plastic strain on the material, which results in structural refinement and strength increase without changing specimen dimensions. As can be seen from Fig. 1, the ARB process consists in repeating of cutting, stacking, and rolling of sheets.

It is known that ARB processing leads to the formation of a lamellar structure at high strains [2], and that the conversion of low-angle to high-angle boundaries dominates over grain refinement [3]. The ARB was successfully performed on commercial purity aluminum, some aluminum alloys and interstitial free (IF) steel [1], [2], [3]. Twin-roll cast (TRC) alloys, having a fine grain structure, have not yet been used for ARB.

The paper reports first experience with the application of ARB procedure in the preparation of ultra-fine grained (UFG) materials from a TRC Al–Fe–Mn–Si alloy (AA8006). The development of UFG microstructure during ARB processing was observed using scanning electron microscopy (electron backscatter diffraction—EBSD) and transmission electron microscopy (TEM). The strength of ARB sheets was evaluated by microhardness measurements.

Section snippets

Experimental details

The experimental material, a twin-roll cast strip of AA8006 alloy, was supplied by AL INVEST Břidličná, a.s., Czech Republic. Its chemical composition is in Table 1. In order to obtain an O-temper material, the strip was annealed for 0.5 h at 400 °C. Two pieces of the strip with dimensions of $250 mm ×50 mm ×2.5$ mm were stacked to form a 5 mm thick specimen. Before stacking, the surfaces of the strips were degreased (in tetrachlorethylene) and wire-brushed (stainless steel brush with wire of 0.3 mm in

EBSD

Fig. 2, Fig. 3 show EBSD orientation maps recorded on the longitudinal cross-sections of the sheets. In the initial material, a relatively large area of $500 μm ×500$ μm was scanned with a coarse step of 3 μm. Equiaxed grains with mean size of 16 μm were observed (Fig. 2). In order to detect the grain refinement resulting from ARB processing, a much finer step (0.2 μm) was used for the analysis of the processed samples.

In consequence, much smaller areas ( $80 μm ×80$ μm) were scanned to achieve a reasonable

Summary

First experience with ARB processing of TRC AA8006 alloy was acquired. After initial failures to achieve good sheet bonding, five cycles of ARB at 200 °C were successfully performed. The hardness of the alloy considerably increased after the first two cycles, but during subsequent ARB processing it rose only slightly. EBSD analysis showed important grain refinement even after two cycles of ARB. TEM observations confirmed that low-angle subgrain boundaries converted of to high-angle grain

Acknowledgements

This research was supported by the Grant Agency of the Czech Republic (project No. 106/03/0790), and in part by the EUREKA program (Project EU 2530 CONTCASTCALTRANS). The experimental material was kindly supplied by AL INVEST Břidličná, Czech Republic. Professor Claude Prioul, École Centrale Paris, kindly enabled the use of the EBSD facilities.

References (6)

Y. Saito et al.
Acta Mater.
(1999)
X. Huang et al.
Mater. Sci. Eng.
(2003)
K.-T. Park et al.
Mater. Sci. Eng. A
(2001)

There are more references available in the full text version of this article.

Cited by (32)

Effect of isothermal multidirectional compression on microstructure and mechanical properties of Al–Zn–Mg–Cu–Zr alloy with minor Sc addition
2024, Materials Chemistry and Physics
Sc microalloying and isothermal multidirectional compression (IMC) are important methods to refine grains and improve the mechanical properties of Al–Zn–Mg–Cu–Zr alloys. Herein, EBSD, SAXS and TEM have been carried out to investigate the effect of IMC and minor Sc on the microstructure, especially for grain boundary wetting, and mechanical properties of aged Al–Zn–Mg–Cu–Zr alloys by melting and hot compression process parameter optimization. The results show that the strength and plasticity can be obviously improved simultaneously by minor Sc addition and IMC. Especially, stripy GBs (one kind of typical GB complexion) have been widely observed for alloy samples after microalloying Sc and IMC, which indicates the occurrence of GB wetting for Al–Zn–Mg–Cu–Zr alloy. And the GB wetting degree gradually increases for alloys with only microalloying Sc, only IMC and (microalloying Sc + IMC). Combined with GB wetting, the formation of Al₃(Sc, Zr) due to Sc addition could inhibit the motion of dislocation and grain boundary, which promotes formation and inhibit growth of recrystallized grains, leading to further grain refinement. Besides, GB wetting degree would affect the precipitate distribution, especially for grain boundary precipitates. Also, GB wetting probably promote grain bridging, which is beneficial to improve the yield strength and ductility of Al–Zn–Mg–Cu–Zr alloys. The concurrent effect of grain refinement, the precipitate including finer Al₃(Sc, Zr) particles, dislocation strengthening and grain bridging contribute to the simultaneous improvement of the strength and ductility of Al–Zn–Mg–Cu–Zr alloys under IMC and Sc. This study provides a new understanding on microalloying Sc combined with IMC on the microstructure and properties of Al–Zn–Mg–Cu–Zr alloys.
Effect introduced high density of precipitates on the microstructural evolutions during multi-direction forging of Al–Zn–Mg–Cu alloy
2020, Materials Science and Engineering: A
Citation Excerpt :
The most commonly accepted mechanism for SPD grain refinement is based on the dislocation cell structure, which are formed at early stages of deformation and gradually transformed to the final fine grain structure. Equal channel angular (ECAP) [4–9], accumulative roll bonding (ARB) [10–15] and multi-directional forging (MDF) [16–22], are the most highly developed SPD processing technologies. Other processing technologies were also employed to refining grains, such as dual-straining by constrained groove pressing [23] and constrained groove pressing [24,25].
Large number density of coarse precipitates were introduced into the Al–Zn–Mg–Cu alloy by interrupted aging and then over-aging at 300 °C. Both the overaged and homogenized samples were isothermal MDFed at 5 × 10⁻³ s⁻¹ with temperatures ranging from 300 °C to 450 °C to investigate the effect of high number density of precipitates on the microstructural evolutions. The results showed that the precipitates decreased gradually during MDF of overaged samples at 300 °C and 350 °C while they were almost dissolved at 400 °C and 450 °C. And as the result of that the precipitates could pin dislocations during deformation, and much greater grain refinement was achieved during MDF of overaged samples at 300 °C and 350 °C.
Evolution of microstructure and mechanical properties in 2014 and 6063 similar and dissimilar aluminium alloy laminates produced by accumulative roll bonding
2019, Journal of Alloys and Compounds
Citation Excerpt :
ARB is one of the few SPD techniques that can be used to produce sheets of laminated monomaterials (further referred to as similar laminates) and laminated composites (further referred to as dissimilar laminates). Since its development [3], ARB was used to process a variety of metal sheets [4–6]. In order to optimize the material properties further, ARB lately is widely used to produce dissimilar laminates [7].
Aluminium laminates of AA6063, AA2014 monomaterials and AA6063/AA2014 composites were produced by accumulative roll bonding processed up to 6 cycles. The microstructure was studied using electron backscatter diffraction and transmission electron microscopy. It is shown that 6 cycles lead to an ultrafine grained microstructure. The mechanical properties were studied by tensile testing and microhardness measurements. In AA6063 laminates, the strength goes over a maximum at 2 cycles, while in AA2014 it increases up to cycle 2 and then remains almost constant. The laminated composite reaches its highest strength after 1 cycle and then slightly decreases. Microhardness measurements were done to compare the deformation in the layers of the laminated monomaterials with those of the laminated composites. Differential scanning calorimetry was used to study the precipitate evolution and its effect on the mechanical properties during accumulative roll bonding. The strength results are discussed with regard to solid solution, precipitation, dislocation and grain size hardening.
Effect of temperature and strain rate on the grain structure during the multi-directional forging of the Al[sbnd]Zn[sbnd]Mg[sbnd]Cu alloy
2019, Materials Science and Engineering: A
Multi-direction forging (MDF) at strain rates of 10⁻³ s⁻¹, 5 × 10⁻⁴ s⁻¹ and at temperatures ranging from 300 °C to 400 °C were performed in the AlZnMgCu alloy. The grain refinement effect was controlled by dynamic recrystallization mechanism. The continuous dynamic recrystallization (CDRX) mechanism dominated to form fine recrystallized grains in the grain interiors at 10⁻³ s⁻¹ and at temperatures ranging from 300 °C to 360 °C or at strain rate 5 × 10⁻⁴s⁻¹ and at temperatures ranging from 300 °C to 320 °C, respectively. With increasing the total strain, the initial coarse grains were gradually replaced by the fine recrystallized grains. Based on the CDRX mechanism, it can be stated that an increase in the MDF temperature or a decrease in the strain rate resulted in accelerating the occurrence of the grain refinement effect. Further, the discontinuous dynamic recrystallization (DDRX) mechanism was considered to be the main recrystallization mechanism when MDF was performed at high temperatures or while using low strain rates, resulting in the formation of recrystallized grains at the grain boundaries. Several coarse grains were remained even after the total strain was increased to 7. Further, grain refinement was not enhanced when the total strain was increased because of the formation of new recrystallized grains, and the growth of the pre-existed recrystallized grains occurred at the same time based on the DDRX mechanism.
Precipitation behavior of bulk nanocrystalline GW103K alloy induced by surface mechanical attrition treatment
2017, Journal of Alloys and Compounds
Citation Excerpt :
Thus, there forms depth-dependent microstructure in the material after SMAT. The nanocrystalline grains achieved by SMAT involve numerous dislocation and sub grain boundaries on the surface, which are far higher than that obtained by Severe Plastic Deformation (SPD) method [16], including equal channel angular pressing (ECAP) [17], high-pressure torsion (HPT) [18], accumulative roll bonding (ARB) [19]. As compared with SPD ways, SMAT was proved to be an effective way to induce sufficient dislocation without strong texture in magnesium alloy.
Precipitation hardening plays a significant role in improving the strength of Mg-RE (RE = rare earth) alloy due to the formation of precipitates. It is vital to control the precipitation behavior in order to optimize the mechanical properties of Mg-RE alloy. The present study explored one new way to promote the precipitation behavior of GW103K alloy by surface mechanical attrition treatment (SMAT). As compared with the conventional heat treatment, more precipitates could be formed under a shorter aging duration after SMAT, which results in finer grain size and higher micro hardness than the as-extruded one. The promotion of precipitation behavior is attributed to the high dislocation density induced by SMAT, which leads to a low nucleation energy and a high nucleation rate for the formation of precipitate.
Mechanical properties of an AM20 magnesium alloy processed by accumulative roll-bonding
2015, Materials Characterization
This work investigates the influence of up to three cycles of accumulative roll-bonding (ARB) on the microstructure and the mechanical behavior of the magnesium alloy AM20. Two initial material states are studied: an initial twin-roll cast (TRC) state and an initial TRC and subsequently heat-treated (HT) state (400 °C/24 h). The ARB process leads to a reduction of grain size in both material states. Both the TRC and the TRC + HT materials exhibit a stabilized basal texture after ARB, which causes the formation of $\{10 \bar{1} 2\} 〈\bar{1} 011〉$ extension twins under compressive loading in the direction of rolling at quasi-static and dynamic strain rates at room temperature. An increase of 0.2% yield strength and compression strength is the result of texture evolution and microstructure refinement through the ARB process. Strain at failure remains constant in the TRC material states and decreases in the TRC + HT states after roll-bonding. Yield strength and strain at failure exhibit marginal dependencies on the strain rate, whereas the compression strength exhibits a greater dependency on the strain rate.

View all citing articles on Scopus

View full text