Microstructures of AZ61 Magnesium Alloy Solidified via Ultrasonic Vibration Treatment

Abstract

The effects of ultrasonic vibration (USV) on the solidified microstructure of AZ61 magnesium alloy were investigated. The experimental results show that the remarkable microstructural refinement is achieved when the USV was applied to the solidification of the AZ61 alloy. The average grain size is decreased from 263 μm without ultrasonic treatment to 98 μm with USV treatment. The microstructure evolution reveals that the primary α-Mg generates and grows in globular shape with USV, contrast with the dendritic shape without USV. The USV causes melt convection during solidification, which makes the temperature of the whole melt homogenized, and produces an undercooling zone in front of the liquid/solid interface, which makes the nucleation rate increased and big dendrites prohibited. In addition, the β-phase in the entire cross-section of the billet is significantly refined and also changed from continuous to discontinuous morphology. Spherical β-phase is formed during the solidification of billet treated with USV.