Revealing the grain size dependent hot workability and deformation mechanisms in a Mg-Zn-Y alloy

Abstract

Despite the industrial significance of grain size for enhancing mechanical properties and formability, the in-depth deformation mechanisms at elevated temperature are still unclear. To investigate the functions of grain size on hot workability and deformation mechanisms, three groups of Mg-1.2Zn-0.2Y alloy specimens with different grain sizes were hot compressed and then studied by combining constitutive model, processing map and microstructural observations. The results showed that the enhanced hot workability accompanying low deformation activation energy and small instability regime was obtained with refined grain size. During hot deformation, the decreased grain size in Mg-1.2Zn-0.2Y alloy mainly improved the plastic deformation homogeneity, especially for the weakened local straining around grain boundaries. As a result, the dynamic recrystallization nucleation and texture development at lower strain level were influenced by the initial grain size. At higher strain magnitude, the growth and coarsening of dynamic recrystallized grains would further release strain localization and improve hot workability, while the texture was less impacted. Further, unlike the primary basal slip and deformation twinning in the specimen with coarse grain at low temperature, non-basal slips of dislocations were initiated with less deformation twins in the specimens with refined grain size.