Ultrasonic treatment for fragmentation at solidification of aluminum alloy

Dendrite that is formed during casting and has a large grain and many branches is harmful structure in metal. In order to suppress generating dendrite structure during casting, an active method was introduced by using high power ultrasound to break dendrite arms and to increase the number of nuclear seeds. AC4CH is one of aluminum alloy which is applied to the casting product like alloy wheel for cars. In this study, high power ultrasound was introduced into molten aluminum during solidification of aluminum dendrites. Then the grain size was analyzed after solidification with different power of the ultrasonic treatment. The grain sizes of the aluminum treated by the high power ultrasound were decreased and the shape became spherical. The sizes were same at the different power of ultrasound when the power approached threshold level. There was also harmful small cavities created when the power of ultrasound exceed required power range. This useless extra ultrasonic power generated vapors of molten aluminum and these vapor was fixed as small cavities in the solid aluminum after solidification.