Strengthening Mechanisms in Mg₉₇Zn₁Y₂ Alloys

Abstract

We elucidate the strengthening mechanisms of Mg-Zn-Y alloys containing long-periodic stacking ordered (LPSO) structures, based on comprehensive electron microscopy investigations. Kinking of the LPSO structures is not only an important way to accommodate plastic deformation effectively, but also simultaneously strengthens the alloy as a result of microstructural refinement. In addition, kink boundaries in the LPSO structures can effectively restrict propagation of microcracks, benefiting both the alloy’s strength and ductility. Using atomic-resolution imaging, we found that the stacking-faults with Zn and Y segregation and the dynamic dislocation-solute interactions in Mg matrix also play important roles in strengthening the alloys, besides the LPSO structures. The stacking-faults can hinder the generation and propagation of $\{ 10\bar 12\}$ deformation twins, reducing the potential nucleation sites for microcracks. Interactions between solute atoms with dislocations promote the dissociation of both “a” and “a + c” dislocations, leading to nanometer-sized structures similar to GP zones that can act as obstacles for dislocation motion in Mg matrix. Both the wide stacking-faults with Zn and Y segregation formed during solidification, and nanometer-sized stacking-faults produced by dislocation dissociation have significant contributions to the mechanical properties at elevated temperatures.