Microstructure, Tensile Properties and Work Hardening Behavior of an Extruded Mg-Zn-Ca-Mn Magnesium Alloy

A new Mg-2.2 wt% Zn alloy containing 1.8 wt% Ca and 0.5 wt% Mn has been developed and subjected to extrusion under different extrusion parameters. The finest ( 0.48 mu m) recrystallized grain structures, containing both nano-sized MgZn2 precipitates and alpha-Mn nanoparticles, were obtained in the alloy extruded at 270 degrees C/0.01 mm s(-1). In this alloy, the deformed coarse-grain region possessed a much stronger texture intensity ( 32.49 mud) relative to the recrystallized fine-grain region ( 13.99 mud). A positive work hardening rate in the third stage of work hardening curve was also evident in the alloy extruded at 270 degrees C, which was related to the sharp basal texture and which provided insufficient active slip systems. The high work hardening rate in the fourth stage contributed to the high ductility extruded at 270 degrees C/1 mm s(-1). This alloy exhibited a weak texture, and the examination of fracture surface revealed highly dimpled surfaces. The optimum tensile strength was achieved in the alloy extruded at 270 degrees C/0.01 mm s(-1), and the yield strength, ultimate tensile strength and elongation to failure were 364.1 MPa, 394.5 MPa and 7.2%, respectively. Fine grain strengthening from the recrystallized fine-grain region played the greatest role in the strength increment of this alloy compared with Orowan strengthening and dislocation strengthening in the deformed coarse-grain regions.