Solidification of aluminum alloy A356 under ultrasonic vibration

Ultrasonic vibration has been shown to be an effective way of obtaining globular grains but its influence on the nucleation and growth of the grains is unclear. In the present study, thermodynamic simulations were carried out to determine the temperature versus solid fraction curve of aluminum alloy A356. The alloy was then treated at various solid fractions isothermally using ultrasonic vibrations. Initial results indicate that it is difficult to obtain globular grains if the specimens are treated at isothermal temperatures in the mushy zone. This means that dendrite fragmentation may play a less important role in producing globular grains. Applying ultrasonic vibrations to the alloy close to its liquidus temperatures resulted in fine globular grains, if the treated specimens were cooled quickly. The experimental results suggest that nucleation plays a key role in the formation of globular grains when the specimens are under ultrasonic vibrations.