Effect of Extrusion Temperature on the Microsturcture in a Bismuth Modified Magnesium Alloy

Dilute Mg–Bi alloy is a recently developed alloy system with good extrudability and ductility. However, there is a limited understanding of the influence of extrusion temperature on its microstructure when extruded at lower temperatures (≤ 300 °C), which restricts the further enhancement of its mechanical properties. In this work, we investigated the microstructure evolution at multiscale levels (micro-scale, nanoscale, and atomic scale) affected by different extrusion temperatures. The results show that particle-stimulated nucleation by the pre-existed Mg 3 Bi 2 particle can significantly refine the grains (even down to a grain size of ~ 80 nm), and it is a dominant dynamic recrystallized mechanism, especially at 100 °C and 200 °C, though, with negligible influence on the final texture. In addition, dynamic precipitation with nano-sized precipitates (tens of nanometers) occurs in these temperatures, and they can provide the Zenner pinning effect to hinder grain growth. Most significantly, deformation-induced bismuth clusters (which can potentially be tailored to provide significant strengthening without deteriorating the ductility) were observed both in the matrix and at grain boundaries in all the extrusion temperatures. As the temperature increases, the size and the density of these clusters increases. Finally, an attempt at quantification of the strengthening contributions from the grain size, nanoparticles, clusters, and solid solution is provided, indicating the significant effect of extrusion temperature on varying these contributions. Graphical Abstract