Effect of ultrasonic melt treatment on microstructure of A356 aluminium cast alloys

A systematic study of the effect of ultrasonic treatment on the structure of the A356 Al-Si-Mg alloy was carried out. Ultrasonic vibrations were applied to the melt at several temperatures (628 to 608 degrees C) for different periods (0-180 s). The results showed that the ultrasonic treatment is effective in controlling the morphology and size of aluminium grains when applied between 619 to 626 degrees C, and is very effective at 622-625 degrees C, where fine non-dendritic grains are formed. Grain sizes smaller than 60 mu m and roundness values of 0.7 and higher were achieved by 15 s ultrasonic treatment at 623 and 620 degrees C. At higher temperatures, the microstructures are dominantly rosette like and dendritic. At lower temperatures (below 617 degrees C), the samples show inhomogeneous microstructures in terms of grain size and morphology. The current results are useful to set some process parameters for the ultrasonic treatment of liquid Al-Si-Mg foundry alloys prepared for semisolid processing.