Strain-induced phase transformation of an Mn-Al alloy during hot compression

Abstract

The high-temperature deformation of an Mn-Al alloy with a chemical composition of Mn51Al47C2 was assessed using hot compression testing at the temperature range of 600–800 °C and the strain rates ranging 0.001 s−1 to 1 s−1. Optical microscopy (OM), scanning electron microscopy (SEM), electron backscattering diffraction (EBSD) and X-ray diffraction (XRD) analyses were implemented to characterize the samples. It was found that during deformation, the τ phase dynamically transformed into γ2+ β + ε phases and the transformation temperature reduced from the equilibrium value of about 790 °C down to < 750 °C. In such temperature range, considering the lower strength of the produced phases, the dynamic strain-induced phase transformations caused a flow softening in the stress-strain curves. However, deformation at temperatures lower than 700 °C, in the state of τ phase stability, led to dynamic recrystallization which was responsible for flow softening. The standard approach was applied to calculate the processing maps which represented an optimal working region in the temperature range of 650 °C up to 700 °C with the strain rates lower than 0.1 s−1 in order to avoid flow localization and dynamic phase transformations.