Achieving high-strain-rate and low-temperature superplasticity in an ECAP-processed Mg-Y-Er-Zn alloy via Ag addition

The effect of adding a small amount of Ag on the microstructure evolution and superplastic properties of Mg-Y-Er-Zn (WEZ612) alloys was systematically studied. The basal texture of the refined WEZ612 alloy produced by equal channel angular pressing was altered to a non-basal structure upon the addition of Ag. Ag addition also refined the grain size and promoted the formation of a large number of nano-14H-long period stacking ordered phases. Using high-resolution transmission electron microscopy, many nano-precipitated phases were detected on the basal plane of the Mg-Y-Er-Zn-1Ag (WEZ612–1Ag) alloy, The nano-precipitated phases on the basal plane improved the thermal stability of the alloy, lowered the deformation activation energy (Q), and improved the stress sensitivity index (m). At 523 K with a strain rate of 10−2 s−1, the Q value of WEZ612 was higher than that of WEZ612–1Ag (299.14 and 128.5 kJ mol−1, respectively). In contrast, the m value of the WEZ612 alloy (0.16) was lower than that of the WEZ612–1Ag alloy (0.46). At 623 K with a tensile rate of 10−2 s−1, the WEZ612 and WEZ612–1Ag alloys were elongated by 182% and 495%, respectively, with the latter exhibiting high-strain-rate and low-temperature superplasticity. The improved superplasticity of the WEZ612-1Ag alloy is attributed to the nano-precipitated phases, which effectively limit the cavity extension during superplastic deformation.