The atomic-structure changes in Al-16 pct Si alloy above the liquidus

The atomic-structure changes in an Al-16 pct Si alloy above the liquidus have been studied by a θ-θ high-temperature X-ray diffractometer, rapid solidification, a vertical centrifugal casting apparatus, and differential scanning calorimetry (DSC) measurements. It was found that the diffraction intensity and structure-factor (S(Q)) curves for an Al-16 pct Si alloy have small prepeaks at small Q values when the temperature is high enough. Rapid-solidification and centrifugal-casting experimental results show that the primary silicon phase can easily coarsen and segregate under additive force after an overheat at high temperatures. The DSC measurements show that the temperature and latent heat of primary solidification rise with the temperature of overheating. These experimental results suggest that a strong interaction occurs between Si-Si atoms in a liquid Al-16 pct Si alloy at high temperatures, resulting in the microsegregation of Si atoms in the melt.