Effect of ultrasonication on the microstructure and macrosegregation of a large 2219 aluminum ingot

By applying ultrasonication during direct chill casting, a 2219 ingot with a diameter of 1250 mm was successfully produced. To study ultrasonic inner mechanism of ingot, the microstructure and macrosegregation of ingots cast after ultrasonication were analyzed by optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and direct-reading spectrometry. The results show that the cavitation and acoustic streaming effects brought by ultrasonic vibration can obviously regulate the structure and refine the grain size of the resulting ingots. The central grain refinement rate observed is 39.6%. Ultrasonication promotes the formation of branched intergranular secondary phases with a discontinuous distribution, and transgranular precipitates present a dispersed distribution with dot. Ultrasonication also effectively decreases negative segregation near the surface of the ingots, reduces the difference solute concentration between their edge and center, and weakens fluctuations in concentration over the entire cross section of the samples, thereby improving the macrosegregation properties of the final products.