Effect of Cyclic Expansion-Extrusion Process on Microstructure, Deformation and Dynamic Recrystallization Mechanisms, and Texture Evolution of AZ80 Magnesium Alloy

Yong Xue,Haijun Liu,Luying Ren,Shuaishuai Chen,Bing Bai,Zhimin Zhang

doi:10.1155/2019/3268276

Yong Xue, Haijun Liu + Show 4 more

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https://doi.org/10.1155/2019/3268276

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Abstract

The microstructure, deformation mechanisms, dynamic recrystallization (DRX) behavior, and texture evolution of AZ80 magnesium alloy were investigated by three-pass cyclic expansion-extrusion (CEE) tests. Optical microscopy (OM), electron back-scattered diffraction (EBSD), and X-ray diffraction (XRD) were employed to study microstructure, grain orientation, DRX mechanism, and texture evolution. The results show that the grain sizes decrease continuously with the increase of CEE pass. The grain refinement effect of the first pass is the most remarkable, and there appear a large number of twins. After three-pass CEE, a well-distributed structure with fine equiaxed grains is obtained. With the increase of CEE pass, the deformation mechanism changes from twinning to slipping and the DRX mechanism changes mainly from twinning-induced dynamic recrystallization (TDRX) to rotation dynamic recrystallization (RDRX) and then to continuous dynamic recrystallization (CDRX). The grain misorientation between the new grains and matrix grains deceases gradually, and a relatively small angle misorientation is obtained after three-pass CEE. Grain misorientations of the first two passes are attributed to TDRX and RDRX behaviors, respectively. The grain refinement changes the deformation and DRX mechanisms of CEE process, which leads the (0002) basal texture intensity first decrease and then increase suddenly. Eventually, the extremely strong basal texture is formed after three-pass CEE.

Highlights

Due to their low weight, high specific strength, and fatigue strength, magnesium alloys have attracted significant interests in a variety of technology-related applications, especially in automotive and aerospace products [1, 2]
E samples used for the microstructural observation were taken from the longitudinal section of the cyclic expansion-extrusion (CEE) deformed sample, as shown in Figure 3. e optical microstructure of the samples was analyzed by using the ZEISS image metallographic microscope. e electron back-scattered diffraction (EBSD) study was conducted on SU5000 scanning electron microscopy (SEM) equipped with an EBSD testing system. e (0002) and (1010) texture was measured by using the D-5000 X-ray test system, and Matlab 2014 software was used to analyze the test data
After two-pass CEE, the grains are further refined, as shown in Figure 4(c), the coarse grain size is less than 10 μm, and the fine grains are especially tiny. e coarse grains are surrounded by massive fine grains, and there appears local severe deformation zone with fine grains. e previous twins almost completely disappear. e above microscopic morphology is highly consistent with the microstructure characteristic of the RDRX mechanism proposed by Ion et al [26]. e RDRX mechanism holds that the new fine grains along or around the boundaries of initial coarse grains are first formed from the rotation of the initial subgrains. e orientation of new grains is greatly different from that of initial grains, forming a large deformation belt or ductile shear zone

Summary

Introduction

Due to their low weight, high specific strength, and fatigue strength, magnesium alloys have attracted significant interests in a variety of technology-related applications, especially in automotive and aerospace products [1, 2]. E severe plastic deformation at high temperature can refine the grains size, which will improve the deformation ability at room temperature of the alloy. During CEE, severe plastic deformation is applied to the material, and significant grain refinement was achieved [11], which will enhance the mechanical performance of the studied alloy. Slipping and twinning are two major deformation mechanisms of Mg alloy [12] and can significantly affect the texture evolution [13]. Deep studies about twinning, grain orientation, and DRX mechanism contribute to the understanding of the microstructural and texture evolution of Mg alloy during CEE. With the help of OM, EBSD, and XRD technologies, microstructure observations were carried out to analyze the twinning, crystallographic orientation, and DRX behavior during CEE process and the relationship between CEE and texture evolution is investigated. Upper plate Lower female die Figure 1: Drawing of the CEE die

Materials and Experiments

Results and Discussion

Conflicts of Interest