a b s t r a c tA flat plate sonotrode was used for ultrasonic melt processing (degassing) of aluminum melts. Calculations showed that this sonotrode should have several antinodes with maximum amplitude, spaced at 16.5 mm. The direct measurements of the amplitude in air and indirect measurements of foil cavitation erosion in water validated these calculations. Unique acoustic measurements of cavitation activity in water and a liquid aluminum alloy were performed using a cavitometer and confirmed that the cavitation conditions were met with this scheme. The melt degassing efficiency using the plate sonotrode was significantly higher (70-80%) than with a conventional cylindrical sonotrode (45-50%) in batch operation. The new scheme was also suitable for ultrasonic melt processing in the melt flow giving about 50% degassing efficiency, which opens the way to upscaling this technology to treat larger volumes of melt.

A continuous high-shear melt conditioning twin-roll casting process has been developed for production of recycled aluminum alloy strip with minimum casting defects. High-shear melt conditioning is applied to increase the impurities tolerance of recycled aluminum. The results of this study showed that solidification during twin-roll casting can be controlled by using intensive melt conditioning prior to casting, which can promote equiaxed growth with minimal defects and result in improved sheet quality. Melt-conditioned twinroll cast (MC-TRC) AA5754 alloy exhibited fine equiaxed grains and homogenized matrix structure while centerline segregation was eliminated. As-cast melt-conditioned twin-roll cast AA5754 strips showed clear grain recrystallization after thermomechanical treatment at 430°C for 30 min, representing an improvement over conventional twin-roll casting. The MC-TRC strip showed 57.2% higher elongation and 4.1% higher ultimate tensile strength compared with the TRC strip after applying melt conditioning with thermomechanical treatment.

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In this paper the effect of Ca on the formation of Si phases during solidification of commercial purity Al-15Si alloy was studied. The Ca impurity level of the commercial purity alloy was 200 ppm which was sufficient to lead to a modified Al-Si eutectic. After the addition of K2SiF6 flux the Ca impurity level was 20 ppm which was insufficient to modify the eutectic Si, but primary Si was refined from 48 µm to 20 µm. The refinement of primary Si in Al-15Si alloy fluxed with K2SiF6, suggests that when Ca level is reduced to less than 20 ppm the impurity level of P (≈20 ppm) in commercial purity hypereutectic Al-Si alloys is sufficient to refine the primary Si without any deliberate addition of P. In the case of adding 0.5 wt.% Ca to the Al-15Si alloy, the eutectic Si was highly modified and the primary Si was coarse and irregular in morphology (unrefined). The addition of such a high level of Ca led to enhanced quantities of entrained oxide inclusions/bifilms. The first phase to solidify was Al2CaSi­2 which nucleated on the oxide bifilms. Primary Si then formed by nucleation and growth on the Al2­CaSi2 particles.