Possible Effects and Mechanisms of Ultrasonic Cavitation on Oxide Inclusions during Direct-Chill Casting of an Al Alloy

Abstract

Oxide films or inclusions can reduce the continuity and integrity of materials and they always lead to a significant reduction in the mechanical properties of an aluminum alloy. They can greatly reduce the plastic flow behavior of materials, thus affecting the subsequent processing performance. Therefore, an effective ultrasonic assisted preparation technology has been applied to industrial manufacturing of large-scale aluminum alloy ingots (with diameter: Φ = 1250 mm and height: h = 3750 mm). However, the mechanisms of ultrasonic purification on the large-scale ingots are not clear. Therefore, a number of aluminum alloy casting experiments were carried out to produce a conventional hot top semi-continuous ingot (CHTI) and an ultrasonic hot top semi-continuous ingot (UHTI) in this work. The microstructures of CHTI and UHTI were analyzed by optical microscopy (OM) and scanning electron microscopy (SEM). The results indicated that there were some oxide film defects in the CHTI but some finely dispersed inclusion particles were discovered in the UHTI. The X-ray diffraction (XRD) data showed that the component of inclusion was Al2O3. According to the different cavitation effects of the different areas of the molten aluminum, the process of ultrasonic purification was divided into three periods and the mechanisms in each period were separately studied.

Ultrasonic Vibration as a Primary Mixing Tool in Accelerating Aluminum–Copper Alloys Preparation from Their Pure Elements

“…Referring to the experiment in water in the current study ( Figure 5), a number of tiny particles floated to the surface of the water during USV. Based on that, after the fragmentation of inclusions, the tiniest of those particles probably moved along the cavitation bubbles and floated to the surface; this assumption is in consonance with the suggestions of Zhang et al [29]. In general, melt processing by USV promoted the quality of the alloys by noticeably reducing the content and sizes of defects, however, the direct contribution of grain refining should be considered as well in reducing the pores sizes [30].…”

On the Nature of Hydrodynamic Cavitation Process and Its Application for the Removal of Water Pollutants

“…6 The most accepted mechanism for cavitation-driven water disinfection and/or detox processes is high temperature and pressure (ie, 8.9 × 10 4 K and 1.3 GPa) that occur within the cavitation bubbles, which cleave the hydrogen-oxygen bond and cause generation of hydroxyl radicals. 7 However, high temperature and pressure can also generate the thermal decomposition of organic pollutants either inside or outside of the cavitation bubbles. 7 The HC process occurs in a few milliseconds and is capable of releasing a significant amount of energy.…”

“…7 However, high temperature and pressure can also generate the thermal decomposition of organic pollutants either inside or outside of the cavitation bubbles. 7 The HC process occurs in a few milliseconds and is capable of releasing a significant amount of energy. 3 It has been proposed that the production of cavities during HC is related to the pressure variation in the flowing liquid when variations in the flow area occur.…”

“…Hydroxyl radicals have been suggested being the main reactive oxygen species involved in oxidizing organic pollutants in water. 2,8,9 The proposed mechanism for organic pollutant degradation using HC is 7 H O H OH (3)…”

“…7 However, high temperature and pressure can also generate the thermal decomposition of organic pollutants either inside or outside of the cavitation bubbles. 7…”