Discussions on the Mechanism of Grain Refinement in Ultrasonic Treated Ti Containing Mg-Al Alloys

The present study investigates the role of titanium in grain refinement of Mg-3Al and Mg-9Al alloys. Minor amount of Ti addition (< 1 wt% of Al-Ti master alloy) brings about grain refinement in both Mg-3Al and Mg-9Al alloys. Ultrasonic treatment further improves the grain size reduction in Ti added Mg-Al alloys. The average grain size of Mg-Al alloys are reduced by 20-30 % from the non-refined alloy by the addition of 1 wt% of Al-Ti master alloy and ultrasonic treatment further enhances the grain refinement by 10-20 %. In addition, ultrasonic treatment transforms the network type beta-Mg17Al12 phase into fine discontinuous precipitates in Ti containing Mg-9Al alloys. The mechanism of grain refinement in ultrasonic treated Ti containing Mg-Al alloy is discussed in terms of solute and heterogeneous nucleation perspective.