Real time synchrotron X-ray observations of solidification in hypoeutectic Al-Si alloys

This paper demonstrates how recent advances in synchrotron technology have allowed for the real-time X-ray imaging of solidification in Al-Si alloys, despite the small difference in atomic number of these elements. The experiments performed at the SPring-8 synchrotron, involved imaging the solidification of Al-1wt.%Si and Al-4wt.%Si alloys under a low-temperature gradient and a cooling rate of around 0.3 C/s. The nucleation and growth of the primary aluminum grains as well as the onset of eutectic solidification were clearly observed. In the alloys containing Al-4wt.%Si, contrast was sufficient to characterize the nucleation rate and growth velocity of the aluminum grains. The importance of improving observation of solidification in the Al-Si system by increasing the time resolution during critical events is discussed.