Ultrasonic Treatment of a Solidifying Al-Cu Melt in the Presence of Micron-sized Hydrogen Bubbles

摘要

The possibility of dynamic grain refinement of aluminum alloys using high-powered ultrasonic waves in the presence of small hydrogen bubbles in the melt is explored. In this regard, a mathematical model is developed to simulate the dynamic behavior of a hydrogen bubble present in the mushy region of a solidifying aluminium-3.4 wt pct copper alloy melt under various applied ultrasonic pressure fields. Due to violent collapse of a small gas bubble, the melt pressure surrounding the bubble increases very rapidly. If the pressure in the vicinity of the dendrites exceeds a threshold value, dendrite fracturing can take place. Dendrite fragments then can act as nuclei during metal crystallization process. This can lead to refined crystalline structure of the metal. This study demonstrates that even far from the bubble's surface, the melt pressure can be sufficiently high to fracture the dendrite arms and produce nuclei for equiaxed crystal growth.