Microstructure and texture characteristics of ZK60 Mg alloy processed by cyclic extrusion and compression LIN Jin-bao(林金保) 1, 2 , WANG Qu-dong(王渠东) 1 , CHEN Yong-jun(陈勇军) 3 , LIU Man-ping(刘满平) 1 , H. J. ROVEN 3 1. National Engineering Research Center for Light Alloy Net Forming and State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University, Shanghai 200240, China; 2. School of Applied Science, Taiyuan University of Science and Technology, Taiyuan 030024, China; 3. Department of Materials Science and Engineering, Norwegian University of Science and Technology, Trondheim 7491, Norway Received 23 October 2009; accepted 9 August 2010 Abstract: The microstructure and crystallographic texture characteristics of an extruded ZK60 Mg alloy subjected to cyclic extrusion and compression (CEC) up to 8 passes at 503 K were investigated. The local crystallographic texture, grain size and distribution, and grain boundary character distributions were analyzed using high-resolution electron backscatter diffraction (EBSD). The results indicate that the microstructure is refined significantly by the CEC processing and the distributions of grain size tend to be more uniform with increasing CEC pass number. The fraction of low angle grain boundaries (LAGBs) decreases after CEC deformation, and a high fraction of high angle grain boundaries (HAGBs) is revealed after 8 passes of CEC. Moreover, the initial fiber texture becomes random during CEC processing and develops a new texture. Key words: ZK60 Mg alloy; cyclic extrusion and compression; electron back scatter diffraction (EBSD); microstructure; texture 1 Introduction Magnesium alloys have attracted considerable interest from the automobile industry because of their low density and high specific strength. Nevertheless, as structural components in automobiles, the material should exhibit both sufficient ductility and attractive specific strength since components may fail by fracture due to shear or tensile forces[1−5]. Thus, the relatively low strength and ductility of Mg alloys due to the hexagonal close packed (HCP) structure with limited slip systems is a major difficulty that hinders their widespread application[1]. Recently, it has been demonstrated that the plastic deformation of Mg alloys is strongly influenced by their texture as well as their grain size. The ductility of Mg alloys may be significantly enhanced by texture control and grain refinement through severe plastic deformation (SPD) such as equal channel angular pressing (ECAP)[2, 6], cyclic extrusion and compression (CEC)[1, 7−10] and accumulative roll bonding (ARB). As a continuous SPD processing, CEC seems more adaptable for industrial applications. Moreover, it is very suitable to refine grains of hard-to-deform metals such as Mg alloys since it imposes three-dimensional compression stresses during processing[3, 11−13]. Our previous results demonstrated that the tensile ductility of ZK60 alloy increased with the increase of CEC accumulated strain. However, the strength shows an opposite trend though the grain size is reduced[1, 3], i.e. exhibiting a reverse or inverse Hall-Petch relation. Similar results in CEC AZ31 alloy[12] and ECAP AZ31 alloy[2] were also reported. Its underlying mechanism is complicated and maybe relevant to grain boundary sliding, texture evolution, grain refinement, twinning, dislocation density and so on. Much more research is needed to investigate the microstructure characteristics of SPD processed metal materials to reveal the relationship between microstructure and mechanical properties. Therefore, the aim of the present study is to investigate the microstructure and crystallographic Foundation item: Projects(50674067, 51074106) supported by the National Natural Science Foundation of China; Project(09JC1408200) supported by the Science and Technology Commission of Shanghai Municipality, China Corresponding author: WANG Qu-dong; Tel: +86-21-54742715; E-mail: wangqudong@sjtu.edu.cn DOI: 10.1016/S1003-6326(09)60421-0