Fig. 1 a Device, b result of thermal analysis for determining the dendrite coherency temperature (TDCP) (Tc and Te refer to the temperatures in the center and near the edge of ingots, respectively)

Fig. 2 Optical microstructures of a K1, b ZK11, c ZK31, d ZK41, e ZK51 alloys

Fig. 3 EBSD observations of a K1, b ZK11, c ZK31, d ZK41 e ZK51 alloys, f the detailed grain sizes variation

Fig. 4 BSE observations of a K1, b ZK11, c, d ZK31, e, f ZK41 g, h ZK51 alloys (the black and white arrows in the enlarged views indicate the Zr-rich areas and Zr particles, respectively)

Fig. 5 Thermodynamic calculated phase diagram of Mg-xZn-0.5Zr alloys

Fig. 6 Phase fraction evolution of ZK31 alloy during solidification with Scheil simulation

Fig. 7 a Zn content, b Zr content in the remaining liquid phase during Scheil simulation

Fig. 8 a Plots of the constitutional undercooling against solid-phase fraction of Mg-xZn-0.5Zr (x = 0, 1, 3, 4, 5 wt%) alloys at the initial stage of solidification ,b the calculated Q values variation against Zn content

Fig. 9 Plot of the measured grain size against 1/Q of Mg-xZn-0.5Zr (x = 0, 1, 3, 4, 5 wt%) alloys

Fig. 10 a Plots of temperature against solid fraction of Mg-xZn-0.5Zr (x = 0, 1, 3, 4, 5 wt%) alloys calculated by the Scheil simulation, b dendrite coherency solid fractions (fDCPs ) of the alloys obtained from (a)

Fig. 11 a Stress-strain curves, b detailed properties of as-cast Mg-xZn-0.5Zr (x = 0, 1, 3, 4, 5) alloys

Fig. 12 Tensile yield strength experimentally measured and the yield strength contributed by grain size based on the Hall-Petch equation