Microstructure and hot deformation behavior of twin roll cast ZAX210 magnesium wire

The hot deformation behavior of a Mg-2Zn-1Al-0.3Ca (ZAX210) wire, manufactured by twin roll casting was investigated by hot compression tests conducted at different temperatures (250 – 400°C) and strain rates (0.01 - 10 s-1). The analyses of the microstructure and the texture are determined by an optical microscope and scanning electron microscope. A processing map is developed to identify optimal process parameters. The twin roll cast state shows the presence of {101 ̅2} extension twins, {101 ̅1} compression twins, double twins, and a weak prismatic texture. Furthermore, regions with small recrystallized grains as well as a small segregation line extend across the center of the wire. The heat treatment at 420°C for 2 h results in a grain structure, consisting of equiaxed grains with an average grain size of approximately 32 µm in the center and 17 µm at the edges of the wire. The heat treatment further reduces the segregation and weakens the texture by spreading the basal plane along the transverse direction. In contrast to the initial state, only {101 ̅2} extension twins can be observed. The experimental results of the compression tests show that the flow stress increases with higher strain rates and decreasing temperatures. The course of the flow curves indicate that dynamic recrystallization occurs during hot deformation. The activation energy for plastic deformation of the twin roll cast and heat-treated wire is calculated to 150 kJ/mol. The process map identifies optimal process parameters, while deviations from these parameters result in crack formation, primarily at grain boundaries.