Regulation on microstructure and mechanical properties of Mg–Y binary alloys by controlled diffusion solidification

Controlled diffusion solidification (CDS) is a new melt treatment process that creates another alloy by mixing two precursor alloys with different thermal masses. Research on its application to Mg alloys is scarce. Focusing on Mg–xY (x = 2,5,7,10, wt%) binary alloys, this study initially conducted thermodynamic calculations, revealing that all target alloys fulfill the thermodynamic prerequisites for CDS: $G_m^{\mathrm{Max}}\le G_m^{\mathrm{final},\mathrm{liquidus}}.$ Subsequently, the evolution of CDS on microstructure and mechanical properties was systematically studied. The results show that CDS significantly refines the grain size of Mg–Y alloys, with the refinement efficacy intensifying as the degree of superheat decreases. Notably, the Mg–2Y alloy exhibited the most pronounced refinement effect post-CDS treatment, achieving a grain refinement rate of ∼91 % at a superheat of 10 ℃. This remarkable grain refinement can be attributed to CDS’s unique two-stage nucleation mechanism. Furthermore, Mg–Y alloys subjected to CDS treatment exhibit both solid solution strengthening and dispersion strengthening effects simultaneously. Synergistically, the combined effects of fine–grain strengthening, dispersion strengthening, solid solution strengthening, and the back–stress strengthening imparted by the second–phase heterogeneous structure conspire to markedly enhance the mechanical properties of Mg–Y binary alloys subjected to CDS processing. The Mg–2Y alloy exhibited the most significant improvement in mechanical properties, with its yield strength being enhanced by ∼144 % after CDS treatment without losing plasticity.