Deformation behavior and texture evolution in an extruded Mg–1Gd alloy during uniaxial compression

Abstract

This paper reports the deformation behavior and texture evolution during uniaxial compression in an extruded Mg–1Gd alloy with a typical 〈2−1−11〉 fiber texture using the electron backscattering diffraction (EBSD) technique. Extension twinning and basal slip are the dominant deformation modes in the early stage of compressive deformation, which are responsible for the remarkable change of texture components. With increasing strain, the texture is changed from the 〈2−1−11〉 into the 〈0001〉 fiber texture component mainly due to the gradual rotation of c-axes towards the compressive direction caused by basal slip.

Introduction

Conventional wrought magnesium alloys exhibit poor room-temperature formability and ductility, which restricts their wide application. Improving the formability of Mg alloys requires a better understanding of the deformation behaviors and their effect on the texture evolution and mechanical behavior of these alloys. Extensive experimental and simulation studies have been conducted on the deformation behavior of AZ31 magnesium alloy. It was reported that the deformation mechanism of AZ31 alloy was related to the initial texture, grain size, strain path and deformation temperature [1], [2], [3], [4], [5], [6], [7], [8], [9]. For example, in a strongly textured AZ31 alloy with the majority of the basal planes parallel to the compressive direction (CD), {10−12} extension twinning is easily activated due to the low critical resolved shear stresses (CRSS) and high Schmid factor and plays a dominant role in the early stage of compressive deformation [1], [10]. The formation of extension twins leads to the re-orientation of basal planes by ~86°, and contributes to texture evolution [10], [11]. More recently, similar observations have been made by Sarker et al. [12] on the extruded AM30 alloy. In their study, it was found that the compressive deformation along the extrusion direction (ED) resulted in a remarkable change in texture components, indicating that the c-axes always rotated towards the CD due to extension twinning.

Different deformation mechanisms usually lead to different characteristics of flow curves. During an extension twinning-dominated deformation, the flow curve is characterized by a low yield stress and the strain hardening rate curve exhibits three distinct stages [10], [13], [14]. The strain hardening rate decreases rapidly in the first stage, and then increases gradually in the second stage, followed by a gradual decrease in the third stage. In contrast, during a slip-dominated deformation, the flow curve shows a relative high yield stress and a gradual decrease of strain hardening rate [1].

It has recently been reported that magnesium alloy containing rare earth (RE) elements exhibit excellent room temperature formability and ductility, which can be ascribed to the weakening or modification of texture due to RE additions [15], [16], [17], [18], [19], [20], [21], [22]. However, the detailed deformation behavior of these alloys is not well understood. Considering the characteristic texture, the deformation behavior of Mg–RE alloys would be expected to be different from that of AZ31 alloy. For example, Mg–8%Gd–3%Y (GW83) alloy was reported to show a gradual decrease of strain hardening rate during compression, which can be attributed to the less fraction of extension twinning and multiply dislocation activities in compression [13]. Yan et al. [23] proposed that both {10−12} extension twinning and basal slip were the dominant deformation modes during the early stage of tensile deformation at room temperature in a rolled Mg–2.0Zn–0.8Gd sheet with non-basal texture, whereas non-basal slip was also activated during late deformation. In an extruded Mg–RE alloy, a typical 〈2−1−11〉 RE texture with the 〈2−1−11〉 orientation parallel to the ED generally develops, which results in a significant improvement in ductility [15]. More recently, it was suggested that the 〈2−1−11〉 RE texture in Mg–Gd alloy is ascribed to the preferred grain growth in our previous study [24]. However, the deformation behavior of the extruded Mg–RE alloy with a typical RE texture during uniaxial loading has never been reported. The aim of this study is, therefore, to examine the deformation behavior and texture evolution in an extruded Mg–1Gd (wt%) alloy with a typical 〈2−1−11〉 RE fiber texture during uniaxial compression. Another goal of this study is to provide useful information for the simulation study on the deformation behavior of Mg–RE alloy, which would allow us to better understand the deformation behaviors of these alloys.