High-Speed Rolling of AZ31 Magnesium Alloy Having Different Initial Textures Yusuke Onuki, Kenichiro Hara, Hiroshi Utsunomiya, and Jerzy A. Szpunar (Submitted August 8, 2014; in revised form November 3, 2014) It is known that magnesium alloys can be rolled up to a large thickness reduction and develop a unique texture when the rolling speed is high (>1000 m/min). In order to understand the texture formation mechanism during high-strain-rate deformation, high-speed rolling of AZ31 magnesium alloy samples having different initial textures was conducted. The main components of the textures after the rolling were the RD-split basal, which consisted of 10°-20° inclining basal poles from the normal direction toward the rolling direction of the sheet, regardless of the different initial textures. With preheating at 473 K, all the samples were rolled without cracking while all were cracked when preheating was not applied. The optical micrographs and EBSD measurements showed a significant amount of twins and the cracks that developed along the shear bands consisted with laminated twins. Based on the texture simulation using the visco- plastic self-consistent model, it is concluded that the rapid development of the RD-split basal component from the initial basal alignment along the transverse direction was attributable to the tension twinning, f10  12gh  1011i: The effect of the initial texture on the crack formation can be explained by the activation of the twinning system. Keywords dynamic plastic deformation, high-speed rolling, magnesium alloy, shear band, texture evolution, twinning 1. Introduction Magnesium and its alloys are known as the lightest structural materials, which are expected to be used widely in the automotive and aerospace industries. While the develop- ment of die-casting techniques has enabled the application of some relatively small parts, the application of magnesium alloys for large parts like exterior panels is expected to be developed (Ref 1). For this purpose, fabrication of the thin sheets is necessary and they should have satisfactory workability. However, magnesium and its alloys have poor ductility at ambient temperatures. Hence, magnesium has to be hot rolled, and in this process, it is difficult to precisely control the thickness and to avoid the surface oxidization. In addition, the sheet produced by the conventional rolling process has so called basal texture, where the basal plane (0001) is aligned parallel to the sheet plane (Ref 2). This texture prohibits the activation of the easiest slip system, (0001) h11  20i; when the deformation either parallel or perpendicular to the sheet plane is induced. The above problems can be solved by applying the high- speed rolling process (Ref 3, 4). The high-strain-rate deformation produces heat due to the internal friction as well as the friction between the material and the rolls, which increases the temperature of the rolled material. It is reported that the AZ31 magnesium alloy can be rolled up to a thickness reduction of 60% without preheating (Ref 3). Furthermore, the texture formed by this process is the RD- split basal texture with the split angle of 10°-30°, depending on the preheating temperature. Textures with large split angle realize better bending workability for various bending geometries (Ref 4). However, the mechanisms of microstruc- ture and texture formations during the high-speed rolling have not been fully understood. It is known that the plastic deformation mechanism of magnesium alloys is very complex. This is due to high critical resolved shear stresses for prismatic and pyramidal slip systems as well as the important contribution of twinning deformation (Ref 5- 7). The activation of different slip systems (basal, prismatic, and pyramidal) and twinning systems is affected by the initial texture of the material, temperature, and strain rate (Ref 8-11). As a result, the workability and the formation of the texture and microstructure are strongly affected by the deformation conditions. There are a large number of studies about the workability and texture formation of magnesium alloys during quasi-static deformation (Ref 5-11). However, very few studies of high- strain-rate deformation above 10 2 s 1 currently exist. In this study, high-speed rolling of samples having different initial textures is performed in order to understand the workability and texture formation during the high-strain-rate deformation. Yusuke Onuki, Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 1-1 Katahira, 2-chome, Aoba-ku, Sendai 980-8577, Japan; Kenichiro Hara, Materials Research Laboratory, Technical Development Group, Kobe Steel, Ltd., 1-5-5 Takatsukadai, Nishi-ku, Kobe 651-2271, Japan; Hiroshi Utsunomiya, Division of Materials and Manufacturing Science, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan; and Jerzy A. Szpunar, Department of Mechanical Engineering, Uni- versity of Saskatchewan, 57 Campus Drive, Saskatoon, SK S7N 5A9, Canada. Contact e-mail: onuki@tagen.tohoku.ac.jp. JMEPEG ÓASM International DOI: 10.1007/s11665-014-1318-8 1059-9495/$19.00 Journal of Materials Engineering and Performance