Investigation of grain refinement and mechanical properties of nano-TiCN particles reinforced Mg[sbnd]9Al alloy via experiments and sharp-interface model

Abstract

Addition of nanoparticles (NPs) in the casting process can greatly refine the grain structure of Mg-9 wt% Al alloy. In this work, different volumes of NPs were used to investigate their effect on grain refinement and mechanical properties. Experimental characterizations showed that a mixing zone of NPs-α-Mg at dendrite tip is formed, and the NPs mainly locate in the mixing zone and the intergranular region, but rarely in the intragranular area. The results also showed that the NPs localize to the intragranular region possibly by attaching to large-sized oxides. With the addition of a suitable amount of nano-TiCN particles to the Mg9Al alloy, grain microstructure was refined and mechanical properties improved. In addition, the sharp-interface model (SIM) was used to clarify the possible grain refinement mechanisms. SIM simulations showed that the heterogeneous nucleation induced by NPs may not be a dominant grain refinement mechanism at both slow and high cooling rates. The numerically estimated equivalent solute diffusion coefficients significantly decreased with the increase in NP amount, indicating that NP-induced inhibition of solute diffusion, grain growth restriction, and enhancement of multi-wave nucleation together constitute the dominant grain refinement mechanisms. The present research offers meaningful insights for controlling microstructure formation in the nano-TiCN reinforced Mg9Al alloys.