Application of the Eyring Equation in the Evaluation of Semi-Solid Forming-Induced Si Particle Refinement in the Hypereutectic Al-Si Alloys

On the basis of Eyring’s theory of absolute reaction rate, an approach to modeling Si particle refinement acceleration in the semi-solid forming of a hypereutectic Al-Si alloy has been developed. The acceleration variable data used in the present analysis were obtained from a semi-solid compression test using Al-25 mass pct Si alloy cylindrical specimens with a diameter of 15 mm and a height of 15 mm; the test conditions comprised a combination of compression displacements ∆h = 5, 10, and 12 mm; compression rates v = 5, 25, and 125 mm/min; and test temperatures T = 853 K and 863 K (580 °C and 590 °C). The coarse primary Si particle refinement depends on a complex interaction among variables, such as compression displacement, compression rate, and test temperature. The performance of Si particle refinement degraded under higher temperature, slower strain rates, and slower shear rates. The results of the Si particle size are suitably summarized by the Eyring equation as a function of the temperature and the shear rate. The baseline Si particle size and the baseline temperature of Si particle refinement, i.e., the reference temperature, were G _N = 0.27 mm and T _N = 866.4 K (593.4 °C), respectively. The calculated results using this equation correlated well with the observed results. An acceleration factor of Si particle refinement was successfully derived on the basis of this equation and indicated that operating at a higher shear rate and a temperature just above the melting point of eutectic Al-Si alloy are the optimum conditions for refining Si particles.