Solid–liquid interface dynamics during solidification of Al 7075–Al2O3np based metal matrix composites

Abstract

Interactions between the solidification front and the remaining suspended particles take place during solidification of particles reinforced composites. The particles are either engulfed by the solidification front or pushed by the solid-liquid interface. In this study, the relation of distribution and clustering degree of nano-Al 2 O 3 in Al7075 with the microstructure of alloy was investigated by conducting casting experiment. A hydrodynamic model for calculating the critical interface velocity required to push nano-particles by the interface was proposed. In addition, the influence of the nano-particles present ahead of solidification front on interface shape was discussed. Microstructural studies showed that the resulting microstructures of composites depended on the size and degree of nano-Al 2 O 3 clustering. Based on the model, it was found that for particles below approximately 36% of the critical radius, r < 0.36r * = 0.9973 μm, the critical interface velocities were four orders of magnitude lower than those obtained by micron particles, suggesting that smaller particles are easily engulfed by the interface rather than pushed. The experimental results were validated by the prediction of the model. Result showed that the constitutional super-cooling of local melts and the accumulation of solute behind the particle caused formation of a cellular interface.

Constitutive behavior of Al2O3np/Al7075 composites with a high solid fraction for thixoforming

“…Sajjadi et al [2] reported that for the A356 alloy with 1.0 wt.% Al 2 O 3np (50 nm), the compressive strength is 2.13 times larger than that obtained by adding the same amounts of micro-sized Al 2 O 3 particles (20 μm), suggesting that particle size greatly affects the mechanical properties of composites. In our previous study on particle pushing [33], we reported the agglomerates of Al 2 O 3np were easily pushed toward eutectic regions. The presence of agglomerates hindered the flow of liquid phases, thus causing the difficulties in feeding shrinkage porosity.…”

A review on high stiffness aluminum-based composites and bimetallics

“…91,97 The presence of Si in cast Al alloys can improve the dispersion of TiB 2 particles, 98 although the TiB 2 particles are still partially segregated in the eutectic regions because of the pushing mechanism during solidification. [99][100][101] The typical microstructure of Al/TiB 2 composites is shown in Figure 12. The Al-9Si-1Mg-0.7Cu/TiB 2 composite can be produced with clean, smooth, and well-bonded interfaces between the aluminum matrix and TiB 2 particles between 25 and 3,000 nm.…”

A Comparative Study on Microstructure and Mechanical Properties of A356-B4c and A356-Graphite Composites

“…The inadequacy of metals and alloys in providing both strength and stiffness to a structure has led to the development of various composites particularly metal matrix composites (MMCs) [1,2].…”