Strengthening mechanisms and their superposition law in an age-hardenable Mg-10 wt pct y alloy

Very weak grain size dependence of yield strength is observed in a peak-aged Mg-10 wt pct Y alloy, in which the Hall-Petch slope k is only 36 pct of that in pure Mg. Such a low grain refinement strengthening response is considered as a result of strong interaction between different strengthening components, and they do not follow a linear superposition law. To determine quantitatively the superposition exponent in the superposition law, the variation of yield strength with grain size in this alloy was examined as solution treated and as peak aged, respectively. The contributions of each major strengthening component, including solid solution, precipitation, and grain refinement strengthening, were evaluated independently based on the data from microstructural characterization. The calculated superposition exponent is scattered around 1.5 with weak dependence on grain size. Furthermore, the effect of solid-solution and precipitation strengthening on the Hall-Petch parameters was also formulated and discussed.