The Zn/Ni ratio determines the properties of Mg-xZn-yNi alloys

To investigate the mechanism of Zn/Ni ratio affects material properties, Mg-xZn-yNi alloys (x=3.5, 6; y=0.5, 1, 2, 4) were prepared. The results indicate that when the Zn/Ni ratio is approximately 3:1, the high precipitation temperature of the NiZn3 phase and its preferential precipitation provide nucleation sites for other second phases, transforming the second-phase structure from a discrete to a continuous river-like pattern. Additionally, based on the Butler-Volmer equation, the Nernst equation, and Faraday's law, the phenomenon where the corrosion potential shifts the most positively but does not exhibit the strongest corrosion rate is analyzed. For other ratios, alloy performance is directly proportional to alloying level. Specifically, the Mg-xZn-yNi alloy at x=3.5 and y=4 exhibits a 75-fold increase in performance compared to y=0.5; the tensile strength of Mg-xZn-yNi at y=4 increases by 12% and 16% compared to y=0.5, respectively. First-principles calculations reveal that the potential difference between the cathodic phase containing Ni and Zn (work function ΦNi=3.57 eV, work function ΦZn=3.55 eV) and the Mg matrix (Φ=3.66 eV) drives microgalvanic corrosion, and high temperatures further promote the kinetics of the corrosion reaction. The mechanical properties are primarily attributed to Ni promoting the dispersion precipitation of second phases such as MgNi2 and NiZn3, effectively hindering dislocation movement, while the elongation change is not significant. This study provides a theoretical basis for designing high-strength Mg-xZn-yNi alloys with controllable degradation rates.