Effects of texture on anisotropy of mechanical properties in annealed Mg–0.6%Zr–1.0%Cd sheets by unidirectional and cross rolling

doi:10.1016/j.msea.2014.07.089

Materials Science and Engineering: A

Volume 615, 6 October 2014, Pages 324-330

https://doi.org/10.1016/j.msea.2014.07.089 Get rights and content

Abstract

Effects of texture on anisotropy of mechanical properties in annealed Mg–0.6%Zr–1.0%Cd sheets by unidirectional and cross rolling were investigated. The results show that both sheets exhibit typical basal texture and obvious anisotropy. Compared with the unidirectional rolling sheet, a weaker basal texture and more scattering rotated grains are obtained by cross rolling within the sheet plane. Meanwhile, the crossing rolling sheet exhibits lower mechanical properties anisotropy than the unidirectionally rolled one. Taking into account of prismatic 〈a〉 slip and basal 〈a〉 slip as the dominant deformation mechanism for the unidirectional and cross rolling sheets respectively, the effects of texture on anisotropic behavior of both sheets could be explained by the microscopic crystal plasticity theory. Furthermore, the decreased anisotropy in annealed sheet by cross rolling is likely attributed to the weakened basal texture which originated from the specific geometry of cross rolling.

Introduction

As the lightest metallic structural material, magnesium (Mg) and its alloys, which are characterized with high strength, specific stiffness and outstanding damping capacity, have attracted increasing interests in many areas [1]. However, due to the limited slip systems of hexagonal close packed (hcp) structure [2], traditional unidirectional rolling (UR) Mg alloy sheets usually exhibit strong basal texture, which will result in intensive mechanical properties anisotropy [3], [4]. Generally, the anisotropy is highly unfavorable for some subsequent processes such as deep drawing [5]. In order to broaden the application of high-performance Mg alloys sheets, rolling technologies for obtaining Mg alloys with low anisotropy should be developed.

To date, some studies have shown that basal texture of Mg alloys can be suppressed by cross rolling (CR) [6], [7]. Meanwhile, decreasing of anisotropy in cross rolling sheet were also reported in a number of studies [8], [9]. But few of them established an explicit relationship for the weakened basal texture and the decreased anisotropy. A recent study [10] revealed that a rolled Mg–0.6%Zr (weight percent used throughout the text) alloy sheet by cross rolling exhibited lower anisotropy compared with the unidirectional rolling one. Texture of the cross rolling specimen was characterized by weak orientation of basal planes. Taking into account of basal 〈a〉 slip as the dominant deformation mechanism during tensile tests, the study gave a qualitative explanation of mechanical anisotropy for both rolling sheets. However, since basal 〈a〉 slip can provide only two independent slip systems [11], which would fail to satisfy the Taylor criterion [12] requiring five independent easy slip systems for homogeneous, generalized ductility of a polycrystalline aggregate. Therefore, it is insufficient to explain the tensile behavior if only basal 〈a〉 slip is considered.

In this study, the investigated as-annealed Mg–0.6%Zr–1.0%Cd alloy sheets were processed by unidirectional and cross rolling. Within the sheet plane of the rolling sheets, texture characteristics were determined by electron back scattered diffraction (EBSD) and mechanical properties were evaluated by tensile tests at ambient temperature. Taking into account of basal 〈a〉 slip and prismatic 〈a〉 slip as the possible deformation mechanisms, effects of texture on mechanical anisotropy are studied based on the microscopic crystal plasticity theory. Especially, an explicit relationship between the weakened basal texture and decreased planar anisotropy by cross rolling is emphatically discussed.

Section snippets

Experimental procedures

The material of as-cast Mg–0.6%Zr–1.0%Cd alloy was prepared in a resistance furnace by melting pure Mg (99.96%), Mg–25%Zr master alloy and pure Cadmium (Cd) powder under the protective 99% CO₂/1% SF₆ (vol%) mixed gas at 1053 K. The melt was poured into a preheated steel mold at 983 K and then cooled in air.

Rolling experiments were carried out at 693 K on a reversible double-roll mill after the ingots were homogenized at 623 K for 24 h. Schematic diagrams of the investigated rolling modes are

Microstructures and texture characteristics

Microstructures of the annealed Mg–0.6%Zr–1.0%Cd sheets obtained by EBSD are shown in Fig. 2, where (a) unidirectional rolling (UR) sheet; (b) cross rolling (CR) sheet. It can be seen that both sheets are mainly consisted of equiaxed grains and show a uniform microstructure. Average grain size of UR and CR specimens are 23.4 μm and 23.1 μm, respectively. Obviously, there is no appreciable distinction between the grain size of UR and CR sheet. It is worth to notice that the difference in grain

Discussion

Generally, anisotropic behavior of a practical polycrystalline material is affected by the dual influence of single crystal anisotropy and polycrystalline orientation distribution [15]. Before we investigate the effects of texture on mechanical property anisotropy, it is necessary to start with the deformation behavior of a single crystal.

Since mechanical properties for the investigated sheets are evaluated by tensile tests, the corresponding Schmid law applied on a single crystal under

Conclusions

In the present study, unidirectional and cross rolling experiments were conducted to examine the influence of texture on anisotropy of mechanical properties. Main conclusions can be drawn as follows:

(1)
Both sheets exhibited typical {0001} basal textures. Compared with unidirectional rolling, cross rolling apparently weakened the basal texture since the sheet by cross rolling exhibited lower basal texture intensity and the grains were more scattering rotated in sheet plane.
(2)
Both sheets exhibited

Acknowledgment

The authors would like to thank Key Project of Chinese National Programs for Fundamental Research and Development (973 program) and National Natural Science Foundation of China (NSFC) through Projects nos. 2013CB632202 and 51074186, respectively.

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Effects of texture on anisotropy of mechanical properties in annealed Mg–0.6%Zr–1.0%Cd sheets by unidirectional and cross rolling

Abstract

Introduction

Section snippets

Experimental procedures

Microstructures and texture characteristics

Discussion

Conclusions

Acknowledgment

Int. J. Plast.

Acta Mater.

Mater. Sci. Eng. A

Acta Mater.

Acta Mater.

Mater. Sci. Eng. A

Mater. Sci. Eng. A

Mater. Des.

Mater. Sci. Eng. A

Mater. Sci. Eng. A

Mater. Sci. Eng. A

Acta Metall.

Scr. Mater.

Acta Mater.