Hot compression deformation behavior and dynamic recrystallization of a precipitate-free Mg–Bi–Sn alloy

Abstract

The addition of Sn improves the properties of Mg–Bi-based alloys, and can potentially overcome the high-temperature limitations of magnesium (Mg) alloys. However, high-Sn alloying leads to stress concentration during hot extrusion. Hence, in this study, the dynamic recrystallization (DRX) mechanism and hot-deformation behavior of a novel precipitate-free Mg–0.25Bi–0.25Sn alloy during hot compression conducted at 250–400 °C with strain rate of 0.001–1 s−1 were examined in detail by constructing processing maps and deriving constitutive equation. The obtained correlation coefficient was 0.99113, indicating that the proposed method can adequately predict the hot deformation behavior of the studied alloy. The calculated average activation energy was 143.0336 kJ/mol. According to the processing maps, the ideal processing areas corresponded to the conditions of 300–400 °C/0.001 s−1/1 s−1 and 400 °C/0.1 s−1. In addition, a transformation of prismatic slip to pyramidal II slip was observed at 350 °C, and the continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) processes occurred during hot compression. The classification of the dominant DRX mechanisms was based on the Zener–Hollomon parameter (Z). Under high-Z deformation conditions, CDRX and DDRX occurred simultaneously; however, CDRX was the predominant process. Under medium-Z deformation conditions, DDRX was the only DRX process. Under low-Z deformation conditions, DDRX dominated over the DRX mechanism and was partially accompanied by CDRX.

Keywords

• Dilute Mg alloy
• Hot compression
• Processing map
• Constitutive equation
• Dynamic recrystallization