Abstract
Abstract The effect of Zn content on grain growth kinetics of the fine-grained extruded Mg–2Gd–xZn (x = 0, 1, 2, 3 wt%) alloys was investigated by annealing of the as-extruded sheets in the temperature range of 623–723 K for various time durations. Microstructural observations revealed that by adding 1 wt% Zn, the grain growth is significantly hindered, while increasing the Zn content beyond 1 wt% accelerates the grain growth. Evaluation of solute atom concentrations at grain boundaries demonstrated that the slower grain growth of the Mg–2Gd–1Zn alloy is due to the co-segregation of Zn and Gd solute atoms, resulting in a high drag pressure and low grain boundary mobility. For higher Zn contents, the α-Mg matrix is depleted of the Gd atoms due to the formation of the Mg3Gd2Zn3 phase, which had a less significant effect in hindering the grain growth compared to the solute drag effect. The grain growth exponents in the range of 3–5 and Q-values in the range of 63.2–109.6 kJ mol−1 suggested that grain growth is controlled by the grain boundary diffusion. The highest KV in the Hall–Patch relationship was observed for the Mg–2Gd–1Zn alloy, indicating higher resistance of the co-segregated grain boundaries against dislocation pile-ups and slip transfer.
Published Version
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