Fig. 1 The Bridgman-type directional solidification furnace: a schematic structure of the furnace, b the structure of the crucible

Fig. 2 Specimen for tensile tests used in this study (unit in mm)

Fig. 3 Measurements of λ 1 and λ 2 on the longitudinal section

Fig. 4 OM microstructures of the directionally solidified Mg-2.49Nd-1.82Gd alloy under the temperature gradient of 40 K/mm at the growth rates of 10 μm/s a, b, 40 μm/s c, d, and 100 μm/s e, f, respectively (a, c, e longitudinal sections; b, d, f transverse sections)

Fig. 5 Variation of the primary dendrite arm spacing λ 1 a and the secondary dendrite arm spacing λ 2 b with the cooling rate R for Mg-2.49Nd-1.82Gd alloy under G = 40 K/mm

Fig. 6 XRD analysis results of Mg-2.49Nd-1.82Gd alloys

Fig. 7 SEM microstructures of transversal section and phase identification results of directional solidified Mg-2.49Nd-1.82Gd alloys under constant temperature gradient 40 K/mm at different growth rates: a, b 10 μm/s; c, d 40 μm/s; e, f 100 μm/s

Fig. 8 Transversal section TEM microstructures and SAED patterns of directional solidified Mg-2.49Nd-1.82Gd alloys under constant temperature gradient 40 K/mm at the growth rate 40 μm/s: a TEM-BF image, b SAED of the phase A, c TEM-BF image, d SAED of the phase B, e local enlarger of SAED boxed by dash line in d

Fig. 9 EPMA backscatter images and Mg, Nd, and Gd element distribution maps of Mg-2.49Nd-1.82Gd alloy after directional solidification under the growth rate of 10 and 100 μm/s at G = 40 K/mm

Fig. 10 Microsegregation of alloying elements in Mg-2.49Nd-1.82Gd alloy: a element Nd, b element Gd

Fig. 11 The nominal stress-nominal strain curves for the directionally solidified and non-directionally solidified experimental alloy under the same cooling rate of 1.6 K/s

Fig. 12 Mechanical properties of the as-cast experimental alloy under the temperature gradient of 40 K/mm at the growth rate of 10, 40, and 100 μm/s, respectively