Influence of Yttrium Addition on Texture and Deformation Behavior in an Extruded ZM31 Alloy

Abstract

The current “storm” of lightweighting, a revolution in materials, processes, and business models, which is brewing on the horizon of the auto industry, inspires researchers and engineers to develop and apply new wrought magnesium alloys with improved properties. For wider applications in the automotive and aerospace industries, the enhancement of strength, thermal stability and formability of magnesium alloys is required. In recent years, Mg-Zn-Y series alloys have received a considerable attention from the research community due to their improved mechanical properties. The present study was aimed at evaluating the influence of Y addition to Mg-Zn-Mn system based on phase formation, mechanical response and texture development with special attention paid to recrystallization, hot characterization and relative activity. The dissertation evaluated the strain hardening and deformation behavior of as-extruded Mg-ZnMn (ZM31) magnesium alloy with varying Y contents via compression testing at room temperature, 200°C and 300°C. Alloy ZM31+0.3Y consisted I-phase (Mg3YZn6); alloy ZM31+3.2Y contained I-phase and W-phase (Mg3Y2Zn3); alloy ZM31+6Y had long-period stacking-ordered (LPSO) X-phase (Mg12YZn) and Mg24Y5 particles. With increasing Y content the basal texture became weakened significantly. While alloys ZM31+0.3Y and ZM31+3.2Y exhibited a skewed true stress-true stain curve with a three-stage strain hardening feature caused by the occurrence of {10 Ī 2} extension twinning, the true stress-true strain curve of alloy ZM31+6Y was normal due to the dislocation slip during compression. The evolution of flow stress, texture and microstructure during the compression tests has been studied under various conditions of temperature and strain rates. Optical metallography, EBSD techniques and X-ray diffraction were employed to study the microstructural development and texture evolution. The deformation activation energy was calculated and the processing maps were generated to determine the optimum hot working parameters. In addition, viscoplastic selfconsistent model was successfully used to predict the experimental textures. Lastly, the strengthening mechanisms in each Mg-Zn-Mn-Y material are established quantitatively for the first time to account for grain refinement, thermal mismatch, dislocation density, load bearing, and particle strengthening contributions. The present work laid the foundations for a better understanding the role of Y elements on deformation behavior in magnesium alloys.