Ultrasound-assisted dispersion of TiB2 nanoparticles in 7075 matrix hybrid composites

Refinement and dispersion of rigid ceramic particles enhance the mechanical properties of particulate reinforced aluminum matrix composites (PRAMCs). However, nanoparticles are intrinsically clustered or agglomerated together in melts and thereby reduce their strengthening efficacy. Ultrasound cavitation and acoustic streaming can effectively improve the distribution of nanoparticles in melts. In this work, we use synchrotron radiation X-ray computed tomography (SR-CT) to unveil the particle dispersion mechanism by ultrasound vibration treatment (UVT) from three-dimensional perspective. The SR-CT results indicated that the mesoscale agglomerates in a high-strength 7075 aluminum alloys can be eliminated completely upon UVT. Two types of TiB ₂ particles have been identified, termed as micro-size TiB ₂ particles (MTPs) and nano-size TiB ₂ particles (NTPs), which were observed to be aggregated along the grain boundaries and dispersed uniformly within the α-Al grains, respectively. Tensile tests reveal significant strengthening of the composites in the as-cast state, suggesting effective Orowan strengthening. This strength enhancement is attributed to the dispersed NTPs that have been retained after solidification. It is also inspiring to see the concurrent increase in the ductility of the composites after UVT, thanks to the improvement in particle distribution.