Effects of Trace Zn on the Deformation Mechanisms of Mg–Gd–Y–Zr Alloy Investigated by In Situ Synchrotron Diffraction

Addition of trace Zn can impose notable effect on the deformation behavior of Mg–Gd–Y–Zr alloy, while the underlying mechanisms have not been revealed. In the present work, Mg–8.5Gd–2.5Y–0.3Zr (wt%) (0Zn) and Mg–8.5Gd–2.5Y–0.5Zn–0.3Zr (wt%) (0.5Zn) alloys are fabricated by casting and extrusion, to obtain a bimodal microstructure containing fine dynamic recrystallized (DRXed) grains and coarse unDRXed grains. The as‐extruded 0Zn and 0.5Zn alloys are studied by in situ synchrotron diffraction under uniaxial tension and compression to clarify the effect of trace Zn on the deformation mechanisms. It is found that both alloys exhibit stress softening in the basal slip‐favored grains under both tension and compression, and adding trace Zn highly enhances the stress softening. Furthermore, the addition of Zn stimulates the occurrence of discontinuous yielding which is in connection with the stress softening, resulting from the interaction between basal dislocations and solute atmospheres. The tension–compression‐yielding symmetry of the alloy is improved by adding Zn, which is mainly attributed to the suppression effect of γ′ phases and Gd/Y–Zn dimers on tensile twinning. Finally, the addition of Zn can promote the tensile and compressive strength, owing to the strength enhancement of the relevant deformation modes and the increase of the fraction of unDRXed regions.