In-situ observation of the nucleation kinetics and the mechanism of grain refinement in Al-Si alloys (Part I)

The nucleation behavior of primary aluminium phase in a hypoeutectic Al-Si foundry alloy is studied using the 3DXRD microscope during the liquid-solid phase transformation for continuous cooling. Grain nucleation and grain growth for few different casting conditions of a commercial aluminium alloy (A356: Al-7Si-0.4 Mg-0.1Fe-0.1Ti wt.%) were investigated using three dimensional X-ray diffraction microscope (3DXRD) located at ID11 at European Synchrotron Radiation Facility (www.ESRF.eu). To conduct the study a monochromatic hard X-ray beam (energy of 70 keV) with a beam size of 200×200 µm² was used and using a special furnace the microstructure evolution during solidification of a commercial Al-Si foundry alloy (A356) was monitored in-situ. Results gathered from solid fraction information showed adding 0.1 wt.% Ti (as Al-3Ti-B) changes the primary aluminium nucleation temperature and aluminium grain size. Furthermore, it showed that at slower cooling rate (0.04-0.1 K/s) grain refiner can alter the primary aluminium nucleation temperature by 20 °C, whereas at higher rates (2 K/s) this figure was reduced down to 5 °C.