Nanoparticle-inhibited growth of primary aluminum in Al–10Si alloys

Abstract In this study, significant grain refinement of Al–10Si alloys was achieved by rapid growth control induced by nanoparticles (NPs). Microstructure analysis revealed the three distribution types of nanoparticles in the matrix, i.e. intragranular distribution (within the interior of primary α-Al), intergranular distribution (along the grain boundary) and extragranular distribution (within the interior of eutectic structure), and the intergranular distribution is dominant in the matrix. During solidification, a great majority of nanoparticles distributed along grain boundaries can form a layer to restrict grain growth. An analytical model is proposed to predict the grain size of hypoeutectic Al–Si alloys, in which the final grain size can be related to the diffusion-hindrance efficiency of NPs that is proportional to the addition level and the time factor that is inversely proportional to the addition level. Model predictions demonstrate that with increasing NP additions, a more densely-packed nanolayer can be formed more rapidly, thus inhibiting the grain growth more efficiently. NP-induced growth control breaks the heavy barriers set by the inherent limitations of inoculation, and the model yields an insight into the understanding of the mechanism underlying NP-induced grain growth.