Abstract: The synergistic enhancement of strength and plasticity is hard to achieve by adding ceramic particles into cast Al alloys, which has been a long-lasting problem. This is due to the agglomeration of particles, which weaken grain refinement effect and higher stress concentration, ultimately leading to cracking. To improve the particle dispersion and related grain refining effect in cast Al5.4Mg2Si alloy, the multi-layer interfaces characterized by low-misfit interfacial layer between TiB₂ particles and α-Al matrix are designed and constructed. Based on density functional theory and phase diagram calculations, Ti and Nb are identified as optimal elements for promoting the formation of a low-misfit interfacial layer on TiB₂ surfaces, enhancing both wettability and nucleation efficiency of TiB₂ particles. Furthermore, multiscale characterizations have confirmed the pronounced formation of the L1₂-Al₃Ti interfacial layer on the TiB₂ surface at the cooling rate of 700 K/s. The low-misfit TiB₂/L1₂-Al₃Ti/α-Al multi-layer interface improves the grain refinement, particle dispersion, and consequently strength-plasticity synergy of the Al5.4Mg2Si-TiB₂ alloy. Critically, the inherent correlation between the cooling rate and the nucleation kinetics of L1₂-Al₃Ti on TiB₂ is manifested based on the classical nucleation theory. The outcomes of this work verify that multi-layer interface engineering is an effective strategy to achieve the high strength-plasticity synergy for ceramic particle-reinforced cast Al alloys.

Key words: Ceramic particles dispersion, Cast Al alloys, Sub-rapid solidification, Multi-layer interface, Heterogeneous nucleation