EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

During metallurgical processes, gas bubbles can be observed to nucleate at different stages of the processing, and consequently interact with the microstructure. The present research on Al-Cu and Al-Ge alloys, showcases the interaction during solidification between these bubbles and the approaching solidification front through state of the art in situ X-radiography techniques and allows for new insights on the influence of bubbles on the solidifying microstructure. The observed effects comprise bulging of the deformation front towards the bubble, bending of dendrites in front of the bubble, coronal outgrowths surrounding the bubbles. Similarly, during melting, bubbles have been observed to nucleate and move in the gradient/concentration-field across the sample, burrowing their way through the mushy zone and towards the colder side of the material. This stands in contrast to the commonly observed bubble-movement towards the hot side of the material caused by Marangoni-flow fields surrounding the gas pockets. This observation is discussed in terms of surface tension variations with changing temperature and concentration.