Variable-Frequency Ultrasonic Treatment on Microstructure and Mechanical Properties of ZK60 Alloy during Large Diameter Semi-Continuous Casting

Abstract

Traditional fixed-frequency ultrasonic technology and a variable-frequency ultrasonic technology were applied to refine the as-cast microstructure and improve the mechanical properties of a ZK60 (Mg-Zn-Zr) alloy during large diameter semi-continuous casting. The acoustic field propagation was obtained by numerical simulation. The microstructure of the as-cast samples was characterized by optical and scanning electron microscopy. The variable-frequency ultrasonic technology shows its outstanding ability in grain refinement compared with traditional fixed-ultrasonic technology. The variable-frequency acoustic field promoted the formation of small α-Mg globular grains and changed the distribution and morphology of β-phases throughout the castings. Ultimate tensile strength and elongation are increased to 280 MPa and 8.9%, respectively, which are 19.1% and 45.9% higher than the values obtained from billets without ultrasonic treatment and are 11.6% and 18.7% higher than fixed-frequency ultrasound treated billets. Different refinement efficiencies appear in different districts of billets attributed to the sound attenuation in melt. The variable-frequency acoustic field improves the refinement effect by enhancing cavitation-enhanced heterogeneous nucleation and dendrite fragmentation effects.

The Effect of Variable-Frequency Ultrasonic Melting Treatment Technology on Microstructure and Properties of AZ80 Magnesium Alloy

“…The grain refinement effect caused by ultrasonic vibration can be attributed to the cavitation-enhanced heterogeneous nucleation and dendrite fragmentation caused by cavitation effect [9]. According to our previous study, the VUT can both enhance the cavitation effect and acoustic streaming effect [10]. Thus, the VUT presents better grain refinement efficiency.…”

Application of Ultrasonics on Preparation of Magnesium Alloys

“…In this section, we will show you the comparison of traditional fixedfrequency field (SUF), variable-frequency ultrasonic field (VUF), and lowfrequency electromagnetic field (LEF) on DC casting of magnesium alloy. The interaction between LEF and VUF is also discussed [22][23][24]. Figure 16 demonstrates the experimental apparatus for ultrasonic DC casting.…”