Effect of eutectic Si size on the flow behavior and hot processing map of near eutectic Al–Si alloys

Abstract

Flow behavior of three near eutectic Al–Si alloys with the same chemical composition but different average eutectic Si sizes (A1, 1.7 μm; A2, 4.4 μm; A3, 8.2 μm) was investigated by isothermal compression tests conducted on a Gleeble-3500 thermal simulator under four different temperatures (350 °C, 400 °C, 450 °C, and 500 °C) and four different strain rates (0.01 s−1, 0.1 s−1, 1 s−1, and 5 s−1), with a focus on the effect of eutectic Si size. Not only the flow behavior but also the processing map of near eutectic Al–Si alloys are affected by eutectic Si size. The overall trends of the flow stress–strain curves of the three alloys are similar, but their steady flow stresses σs are different: A1 alloy has the largest σs, followed by that of A3. Strain-compensated constitutive equations in the hyperbolic sine form were constructed to describe the flow stress behavior of the three alloys. Materials constants of the constitutive equations depend on eutectic Si size. The processing maps of the three alloys exhibit different characteristics. The instability domain of A2 alloy is restricted to strain rates larger than about 0.4 s−1, in contrast to the case of A1 and A3 alloys in which the instability domain occurs at both low and high strain rates. The results presented in this study indicate that eutectic Si size is an indispensable factor to be considered when dealing with the hot working of Al–Si alloys.