Hot Deformation and Dynamic Recrystallisation Behaviour of Twin-Roll Cast Mg-6.8Y-2.5Zn-0.4Zr Magnesium Alloy

Abstract

In this work, the deformation behaviour of a twin-roll cast (TRC) Mg-6.8Y-2.5Zn-0.4Zr alloy during plane strain compression was characterised by high-temperature testing. Based on the experimental data, the values of strain-rate sensitivity, the efficiency of power dissipation and the instability parameter were investigated under the conditions of various hot deformation parameters. In contrast to conventionally cast material, no lamellae of the LPSO (long period stacking ordered) phase were precipitated in the magnesium matrix after TRC. The precipitation of fine lamellar LPSO phases only occurred during cooling to forming temperature after the heat treatment. Dynamic recrystallization (DRX) hardly occurred during deformation at temperatures between 350 °C and 400 °C. This can be attributed to the precipitation of the lamellar LSPO phases, which contribute to retardation of the DRX process. At higher deformation temperatures and strain rates DRX is pronounced and the twin-induced (TRDX) as well as continuous dynamic recrystallization could be identified as the dominant softening mechanisms. The processing maps were established by superimposing the instability map over the power dissipation map, this being associated with microstructural evolution analysis in the hot deformation processes. Two instability zones could be recognised for the twin-roll cast and heat-treated Mg-6.8Y-2.5Zn-0.4Zr alloy: (1) 350 °C to 460 °C and 0.01 s−1 to 0.3 s−1 and (2) 485 °C to 525 °C and 2.5 s−1 to 10 s−1, where deformation is not favourable.

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

“…When deformation takes place at 350 • C, hardly any DRX occurs. However, it was also found in previous investigations [38] that twin and lamellar LPSO phases occur simultaneously. As the deformation temperature increases, the number of grains exhibiting lamellar LPSO phases decreases.…”

“…The instability of adiabatic shear bands or local plastic flow tends to occur rather than dynamic recrystallization. Consequently, these instabilities result in the formation of microcracks [1,38]. Optimum deformation conditions are temperatures from 500 • C to 520 • C at strain rates ranging from 0.01 s −1 to 0.1 s −1 for the as-cast material and a strain rate of 1 s −1 for the TRC material.…”

Hot Deformation Behavior and Constitutive Analysis of As-Extruded Mg–6Zn–5Ca–3Ce Alloy Fabricated by Rapid Solidification

“…It is clear that lower power dissipation efficiency lies in regions with lower temperature and higher strain rate, which exhibits the typically unstable flow. In the case of a relatively low temperature, DRX can hardly happen, and thus extensive dislocations are inevitably accumulated with increasing plastic deformation, causing severe working hardening [36]. Therefore, this condition trends to induce unstable flow of metallic materials.…”

The Parameters Identification of High-Temperature Constitutive Model Based on Inverse Optimization Method and 3D Processing Map of Cr8 Alloy Steel

“…From the hot forging of materials perspective, we built a 3D processing map including strain because strain can influence it greatly as shown in Shalbafi [ 16 ], who established a 2D processing diagram of Mg-10Li-1Zn alloy at a high temperature and different strains. Madlen Ullmann [ 17 ] established a 2D processing map of Mg-6.8Y-2.5Zn-0.4Zr Magnesium Alloy to identify the unstable areas in the material and found that the adiabatic shear band or the instability of plastic flow had a tendency to occur during deformation. Enxiang [ 18 ] established 2D processing maps of superaustenitic stainless steel S32654 at different temperatures and strains.…”