Abstract
The aerospace and automotive industries are seeking advanced materials with low weight yet high strength and durability. Aluminum and magnesium-based metal matrix composites with ceramic micro- and nano-reinforcements promise the desirable properties. However, larger surface-area-to-volume ratio in micro- and especially nanoparticles gives rise to van der Waals and adhesion forces that cause the particles to agglomerate in clusters. Such clusters lead to adverse effects on final properties, no longer acting as dislocation anchors but instead becoming defects. Also, agglomeration causes the particle distribution to become uneven, leading to inconsistent properties. To break up clusters, ultrasonic processing may be used via an immersed sonotrode, or alternatively via electromagnetic vibration. This paper combines a fundamental study of acoustic cavitation in liquid aluminum with a study of the interaction forces causing particles to agglomerate, as well as mechanisms of cluster breakup. A non-linear acoustic cavitation model utilizing pressure waves produced by an immersed horn is presented, and then applied to cavitation in liquid aluminum. Physical quantities related to fluid flow and quantities specific to the cavitation solver are passed to a discrete element method particles model. The coupled system is then used for a detailed study of clusters’ breakup by cavitation.
Highlights
SEVERAL studies suggest that the addition of nanoparticle reinforcements to light metals significantly enhances their mechanical properties
Another study indicated a slight enhancement in Brinell hardness of aluminum, magnesium, and copper-based MMNCs with Al2O3 and AlN nanoparticles.[2]
The acoustic pressure, velocity as well as cavitation-specific physical quantities are passed on to a discrete element method (DEM)-based particles solver that simulates the behavior of particle clusters close to a pulsating and collapsing bubble
Summary
5616—VOLUME 48A, NOVEMBER 2017 demonstrated in Reference 4. The agglomeration of particles in MMCs is related to the fact that micro- and especially nano-sized inclusions have a large ratio of surface area to volume. This causes surface forces such as van der Waals interaction and adhesive contact to dominate over the volume forces such as, e.g., inertia or elastic repulsion. Assuming the interfacial energy csl = 0.2 to 2.0 J/m2, Eq [1] yields vf =100 to 1000 m/s Such fluid velocity values can be locally achieved instantaneously as a result of the collapse of cavitation bubbles induced by the ultrasonic field. The acoustic pressure, velocity as well as cavitation-specific physical quantities (such as bubble radius and bubble interface velocity and pressure) are passed on to a discrete element method (DEM)-based particles solver that simulates the behavior of particle clusters close to a pulsating and collapsing bubble
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