Fig.1 Creep curves for the WE43(T6) alloy under various stresses at: (a, b) 523 K and (c, d) 573 K. It presents the total strain against time in (a, c) and creep rate against time in (b, d). The cross symbols at the end of the curves indicate that the specimen was crept to rupture

Fig.2 Creep curves for the WE43(T6) alloy at constant stress of 60 MPa under temperature range of 523-573 K: (a) total strain against time and (b) creep rate against time. The cross symbols at the end of the curves indicate that the specimen was crept to rupture

Fig.3 The log-log plot of the stress dependence of minimum creep rate at T = 523-573 K. Note that the previously reported data of WE43(T6) [15,17] and WE54(T6) alloys[17] are also presented for comparison

Fig.4 Arrhenius plot of the logarithm of minimum creep rate against the reciprocal of temperature for applied stress of 60 MPa is shown. Note that the previously reported data of WE43(T6) and WE54(T6) alloys[17] are also presented for comparison

Fig.5 Typical microstructure of the WE43(T6) alloy: (a) optical micrograph and (b, c) TEM bright-field images (the inset in Fig. 5(c) is a corresponding high-magnification image showing the precipitates, and the white and black arrows indicate the β′ and β1 phases, respectively); (d) the corresponding SAED pattern of Fig. 5(c) and the beam direction are approximately along the [0001]Mg axis zone, in which the white circles indicate the locations of diffraction spots from the precipitates

Fig.6 Microstructures of the creep specimen ruptured at condition of 573 K and 35 MPa: (a, b) optical micrographs of longitudinal and shank sections showing the development of PFZs along grain boundaries approximately normal to the stress direction, respectively; (c, d) TEM bright-field image taken from the longitudinal section and the corresponding SAED pattern, respectively. The beam direction is approximately along the [0001]Mg axis zone

Fig.7 TEM bright-field images of solution treated WE43 alloy aged at 573 K for 2 h: (a) and (b) along [0001]Mg and [112ˉ0]Mg axis zones, respectively

Fig.8 SEM images obtained from the longitudinal section of ruptured creep specimens showing the development of directional PFZs along grain boundaries at different creep conditions: (a) 523 K/100 MPa; (b) 548 K/60 MPa; (c) 573 K/60 MPa; (d) 573 K /35 MPa. The average width of directional PFZs is measured as illustrated in the figure

Fig.9 Elements mapping of the grain boundary precipitates and PFZs in the ruptured creep specimen at condition of 573 K and 35 MPa: (a) SEM image; (b-e) the corresponding elements mapping of Mg, Y, Nd and Gd, respectively; (f) concentration of elements along the dot line (point h to point i) in (a)

Fig.10 TEM bright-field images showing the dislocation substructures in the ruptured creep specimen at condition of 573 K and 35 MPa. The incident beam is near [12ˉ13ˉ]Mg in (a), near [21ˉ1ˉ0]Mg in (b) and near [011ˉ0]Mg in (c)

Fig.11 Optical and SEM micrographs obtained from the longitudinal section of ruptured creep specimens showing the fracture mechanism at different creep conditions: (a-c) 523 K/100 MPa; (d, e) 548 K/60 MPa; (f, g) 573 K/35 MPa

Fig.12 Optical and SEM images obtained from the ruptured creep specimens showing the microstructures of the longitudinal section of fractures and fracture surfaces at different creep conditions: (a, b) 523 K/100 MPa; (c-f) 548 K/60 MPa; (g, h) 573 K /35 MPa