Thixoforming of A356/SiC and A356/TiB2 Nanocomposites Fabricated by a Combination of Green Compact Nanoparticle Incorporation and Ultrasonic Treatment of the Melted Compact

Abstract

Thixoforming is a type of semi-solid processing which is based on forming metals in the semisolid state rather than fully liquid or solid state. There have been no reports of the thixoforming of nanocomposites in the literature. The incorporation of ceramic nanoparticles into liquid metals is a challenging task for the fabrication of metal matrix nanocomposites due to their large surface-to-volume ratio and poor wettability. Previous research work by a number of workers has highlighted the challenges with the incorporation of nanoparticles into liquid aluminum alloy. In the present study, SiC and TiB 2 nanoparticles with an average diameter between 20 and 30 nm were firstly incorporated into green compacts by a powder forming route, and then the compacts were melted and treated ultrasonically. The microstructural studies reveal that the engulfment and relatively effective distribution of the nanoparticles into the melt were achieved. The hardness was considerably improved with only 0.8 wt pct addition of the nanoparticles. The nanocomposites were successfully thixoformed at a solid fraction between 0.65 and 0.70. The microstructures, hardness, and tensile mechanical properties of the thixoformed nanocomposites were investigated and compared with those of the as-received A356 and thixoformed A356 alloys. The tensile properties of the thixoformed nanocomposites were significantly enhanced compared to thixoformed A356 alloy without reinforcement, indicating the strengthening effects of the nanoparticles.

Effects of High-Intensity Ultrasound on Microstructure and Mechanical Property of In situ TiB2/2A14 Composites

“…Compared with the ex situ, the particle size of the reinforced phase produced by the in situ is smaller, up to micron or even nanoscale. The micron particle has good compatibility and interfacial bonding with the matrix, and no pollution on the surface, which can further improve the properties of the composites [5][6][7][8][9][10][11].…”

The Application of External Fields to the Manufacturing of Novel Dense Composite Master Alloys and Aluminum-Based Nanocomposites

“…Various techniques were used in the past, e.g., mixing of nanoparticles with aluminum powder followed by extrusion, [12] melting under pressure, [13] or sintering under pressure. [14] The application of such master alloy makes the introduction of particles into the melt easier but does not solve the problem of their agglomeration and dispersion. [14] The application of external fields (e.g., ultrasonic cavitation) can facilitate wetting of the particles, breaking down the particle agglomerates, and homogeneous distribution of the particles throughout the melt volume and, eventually, throughout the billet structure.…”

“…[14] The application of such master alloy makes the introduction of particles into the melt easier but does not solve the problem of their agglomeration and dispersion. [14] The application of external fields (e.g., ultrasonic cavitation) can facilitate wetting of the particles, breaking down the particle agglomerates, and homogeneous distribution of the particles throughout the melt volume and, eventually, throughout the billet structure. [5,6,10] Shock waves were suggested for compacting powders and even making nanocomposite materials through a powder metallurgy route.…”

Microstructure, Mechanical Properties and Wear Behavior of the Rheoformed 2024 Aluminum Matrix Composite Component Reinforced by Al2O3 Nanoparticles

“…When the semisolid slurry was rheoformed in the die cavity, it showed a backward extrusion mode. The flow front of the semisolid slurry in locations A and B is a free surface [27], indicating the lowest resistance to flow. The flow velocity of liquid phase is higher than that of solid phase.…”

“…It is due to the fact that cavitation and acoustic streaming created via ultrasonic wave dispersed Al 2 O 3 nanoparticles uniformly [26,42]. In addition, further dispersion of Al 2 O 3 nanoparticles was obtained via controllable viscosity of semisolid slurries [27][28][29]. However, few Al 2 O 3 nanoparticles were found in the TEM microstructure at a stirring temperature of 630 • C (Figure 13f).…”