A Comparative Study on the Hot Deformation Behavior of As-Cast and Twin-Roll Cast Mg-6.8Y-2.5Zn-0.4Zr Alloy.

Kristina Kittner,Madlen Ullmann,Ulrich Prahl

doi:10.3390/ma14133628

Abstract

The Mg-6.8Y-2.5Zn-0.4Zr (WZ73) alloy exhibits different microstructure characteristic after conventional casting compared to the twin-roll cast (TRC) state. Twin-roll casting results in a finer microstructure, where the LPSO phases are more finely distributed and less strongly connected. A transfer of the hot deformation behavior from the as-cast condition to the TRC condition is only possible to a limited extent due to the microstructural differences. Both states show differences in the recrystallization behavior during hot deformation. In the conventional cast state, dynamic recrystallization (DRX) is assumed to be delayed by the occurrence of coarse blocky LPSO phases. Main DRX mechanisms are continuous dynamic recrystallization (CDRX), particle stimulated nucleation (PSN) and twin induced dynamic recrystallization (TDRX). The deformed TRC sample showed pronounced DRX at almost all deformation conditions. Besides the TDRX and the PSN mechanism, kink induced dynamic recrystallization (KDRX) can be observed. Optimum deformation conditions for both states are temperatures from 500 °C to 520 °C, and strain rates ranging from 0.01 s−1 to 0.1 s−1 for the as-cast material as well as a strain rate of 1 s−1 for the TRC material.

Highlights

Within the last few years, there has been increased research on magnesium alloys with LPSO phases
LPSO phases with an 18R or a 14H structure occur after conventional casting as well as after twin-roll casting (TRC) [1,2,3,4,5,6,7]
The microstructure of both conditions mainly consists of the α-magnesium matrix and network-like LPSO phases located along the grain boundaries

Summary

Introduction

Within the last few years, there has been increased research on magnesium alloys with LPSO (long period stacking ordered) phases. These are known to provide alloys with a good mechanical property profile. The high strength is mainly attributed to the formation of kink bands in the LPSO phase. Several studies have reported the formation of kink bands during plastic deformation for different initial states, such as as-cast or twin-roll cast. LPSO phases with an 18R or a 14H structure occur after conventional casting as well as after twin-roll casting (TRC) [1,2,3,4,5,6,7]

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