Ultrasound induced fragmentation of primary Al3Zr crystals

Abhinav Priyadarshi,Dmitry Eskin,Marcello Conte,John Durodola,Paul Prentice,Tungky Subroto,Koulis Pericleous,Iakovos Tzanakis

doi:10.1051/matecconf/202032604002

Abstract

Ultrasonic cavitation melt treatment (UST) of aluminium alloys has received considerable attention in the metal industry due to its simple and effective processing response. The refined primary intermetallic phases formed in the treated alloys during controlled solidification, govern alloy structural and mechanical properties for applications in the automotive and aerospace industries. Since the UST is performed close to the liquidus temperatures of the alloys, understanding the refinement mechanism of the primary intermetallic phases has been beset by difficulties in imaging and handling of liquid metals. In this paper, the sonofragmentation behaviour of primary intermetallic Al3Zr crystals extracted from the matrix of an Al-3 wt% Zr alloy and fixed on a solid substrate was investigated. The intermetallics were exposed to cavitation action in deionized water at 24 kHz of ultrasound frequency. The fragmentation mechanism from the nearby collapsing cavitation bubbles was studied with in-situ high speed imaging. Results revealed that the main fragmentation mechanism is associated with the propagation of shock wave emissions from the collapsing bubble clouds in the vicinity of the crystal. The mechanical properties of the Al3Zr phase determined previously were used for the fracture analysis. It was found that an Al3Zr intermetallic undergoes low cycle fatigue fracture due to the continuous interaction with the shock wave pressure. The magnitude of the resulting shear stress that leads to intermetallic fragmentation was found to be in the range of 0.6 – 1 MPa.

Highlights

Ultrasound induced cavitation and its possible benefits in liquid metal processing has received considerable attention from both the academic and industrial communities since the 1950’s
From the sequence of images, it is evident that introduction of an ultrasonic wave in a liquid medium leads to the development of acoustic cavitation cloud and emission of periodic high energy shock waves reaching pressures of several GPa and shock velocities up to 4000 m/s [20,21]
It can be seen from the images that as the shock wave S1 propagates further away, another shock wave emerges from a thick cavitation cloud near the ultrasonic horn and the progression continues

Summary

Introduction

Ultrasound induced cavitation and its possible benefits in liquid metal processing has received considerable attention from both the academic and industrial communities since the 1950’s. The two most common in-situ experimental techniques for characterizing materials processed using UST are; (i) high-speed optical imaging of transparent organic liquids/melts, and (ii) X-ray synchrotron radiography of liquid metals. In addition to handling and processing difficulties in analysing real metallic melts through in-situ X-ray synchrotron technique, the radiography method offers a very limited field of view for capturing the dynamic effects of multi-phase interactions

Methods

Results

Conclusion