Unidirectional dendritic solidification under longitudinal resonant vibration

Abstract

Longitudinal steady-state sinusoidal vibration is introduced into the unidirectional dendritic solidification process of Al−3% Mg alloy. The first (470 Hz), second (1050 Hz), and third (1736 Hz) order resonant frequencies of solidification system is utilized to produce strong vibrational response out of less exciting energy. Solidification front temperature is raised by vibration under constant solidification conditions, whereas liquid temperature gradient ahead of solidification front and solidification rate are both reduced. Dendrite fragmentation is the most conspicuous variation of structural morphology, which is characterized by primary stalk disintegration and secondary arm detachment. The first order resonance results in a periodically fractured bamboo-like dendritic structure and most severe solute segregation. Contrary to its grain refinement effect, vibration expedites the coarsening of resultant structures. The alloy mechanical properties are markedly deteriorated under the first order resonance. But they are appreciably improved if the second and third order resonant vibrations are applied.