Development of a Mg-6.8Y-2.5Zn-0.4Zr alloy (WZ73) under varying twin roll casting conditions

Abstract. Twin roll casting (TRC) has a big potential to produce thin strip material from magnesium alloys and enables the production in an economic manner. However, the final properties of TRC strips, such as microstructure and texture, are influenced by the twin roll casting conditions. In this work the development of a Mg-6.8Y-2.5Zn-0.4Zr alloy (WZ73) during different twin roll casting conditions, varying the twin roll casting speed, were studied. As a reference the strain and strain rate were determined. After twin roll casting the microstructure is inhomogeneous over the strip thickness and consists of a network-like structure of the LPSO phases and the α-Mg matrix. The α-Mg matrix is made up of dobulites (flake-like structures), which is already known for this alloy. [1,2] Typical defects of the twin roll cast strips were observed as well. It was also revealed that the twin roll casting conditions have a big influence on the precipitation, morphology, and phase fraction of the LPSO phases. For example, the phase fraction increases with the strain decreasing whilst the thickness of the precipitated phases increases with an increased strain. In all samples kink bands and yttrium enriched precipitations within the network like structures were detected. No dynamic recrystallization nor grain boundaries were detected. The resulting textures revealed the activation of basal slip and non-basal slip, but the intensities are small, regardless of the twin roll casting conditions.