Conventional casting of 5N5 high-purity aluminum often results in coarse grains, microstructural inhomogeneity, and a low equiaxed grain area fraction. Vacuum casting in a graphite mold was integrated with multidirectional mechanical vibration to refine and homogenize the solidification microstructure. A three-factor, three-level Box–Behnken design combined with response surface methodology was employed to optimize pouring temperature (A), mold temperature (B), and vibration frequency (C), with the average grain size (Y1) minimized and the average shape factor (Y2) and equiaxed grain area fraction (Y3) maximized. Analysis of variance indicated statistically significant quadratic models with a non-significant lack of fit. The predicted optimum (A ≈ 714 °C, B ≈ 363 °C, C ≈ 37 Hz) was validated experimentally, producing a refined and highly equiaxed structure (Y1 ≈ 0.85 ± 0.02 mm, Y2 ≈ 0.84 ± 0.04, Y3 ≈ 88.6 ± 2.11%), consistent with model predictions. Multidirectional vibration strengthens melt convection and interfacial shear, which is considered to promote grain multiplication and increase the number of effective nuclei, thereby accelerating the columnar-to-equiaxed transition and improving microstructural uniformity.
Zhang et al. (Fri,) studied this question.
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