In-situ rod-shaped nanoparticles in Mg-Zn magnesium alloy: Towards high strength and ductility

Zinc ingot was added to molten ZK60A magnesium alloy to improve tensile and compressive properties after hot extrusion. In tension, Zn addition increased strength (by up to +71%) and ductility (by +109%). The addition of Zn resulted in significant grain refinement by about 1 order of magnitude, and increased alignment of the basal plane along the extrusion direction (or force axis). More importantly, the addition of Zn enabled the significant formation of rod-shaped intermetallic nanoparticles (β nanorods) responsible for significant strengthening during tensile deformation. The β nanorods were preferentially formed from hetrogenous precipitation of dissolved Zn on finer α nanorods. The observation of non-basal slip in the high strain zone (HSZ) adjacent to the β nanorod (after room temperature tensile deformation) indicated the sufficiently robust nature of the interface between the β nanorod and the alloy matrix. In compression, Zn addition increased strength (by up to +74%) but at the expense of ductility (decreased by −34%). There was buckling and fracture of the β nanorod (loss of strength) during compression but this was offset by the significant grain refinement and increased alignment of the basal plane along the force axis (gain in strength). Also, there was HSZ formation from the tip of one β nanorod to another, but the strain hardening rate was overall higher due to Zn addition, resulting in ductility loss.