Synergistic effects in magnesium-rare-earth-zinc alloys - a gateway to informed alloy design

In dilute magnesium (Mg) alloys, solute effects were proven crucial for microstructure and texture development rendering a deep understanding of solute-solute and solute-defect interactions indispensable for property predictions and alloy design. This dissertation aimed at clarifying the underlying factors contributing to the formation of texture components deviating from the common basal texture in ternary magnesium-rare earth (RE) -zinc (Zn) alloys. The main focus was on understanding the role of solute defect interactions and resulting synergistic solute effects. A multi-scale characterization involving classical electron backscatter diffraction (EBSD) analysis, mechanical testing, and atom probe tomography (APT) was adopted to establish microstructure correlations concerning atomic scale segregation phenomena, slip activation and arising material properties. Binary and ternary dilute Mg-Gd-(Zn), Mg-Er-(Zn) and Mg-Ca-(Zn) alloy sheets were investigated subsequent to rolling deformation and various heat treatments. The results confirmed the formation of a unique ±40° transverse direction (TD) recrystallization texture in ternary Mg-RE-Zn alloys. A texture transition from an RD to an TD dominated texture was found to take place during the early stages of recrystallization. To understand texture selection during recrystallization, further investigations on nucleation and early nucleus growth during static recrystallization were carried out. An as-cast Mg-Gd-Zn sample was subjected to uniaxial compression at 200°C up to 40% strain and subsequently cut into two mirroring sample halves of which one was annealed for 60 min. Classical and quasi-in-situ EBSD analysis proved the importance of specific nucleation sites, especially compression-tension double twins, to the final texture. Quasi-insitu EBSD investigations revealed selective growth of off-basal texture components, which would ultimately dominate the resulting recrystallization texture. Combined solute effects and their dependence on the solute ratio, were ...