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

• A synchrotron technique was used to observe solidification of Al-Si alloys.
• Nucleation, coarsening, and the onset of eutectic solidification were observed.
• Images captured are suitable for quantitative analysis.
• The resolution that was obtained should be possible for most aluminum 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.