On the microstructures evolution and interface structures of Al-17Si-4Cu alloys prepared by spray deposition upon the addition of TiB2

This study investigates the influence of TiB₂ content on the microstructural evolution and interface structure of Al-17Si-4Cu alloy prepared by spray deposition. Using in-situ synthesis of intermediate alloys and a subsequent spray deposition process, we successfully achieved a uniform dispersion of TiB₂ in the melt and prepared Al-17Si-4Cu composites containing 0, 3, and 5 wt% TiB₂ as a reinforcing phase. Various techniques, including XRD, SEM, and TEM, characterized their microstructures and properties. The results indicate that TiB₂ content exerts a significant effect on the material properties: an increase in TiB₂ content leads to a rise in the viscosity of the semi-solid slurry. In the discrete molten droplets (during atomization), high viscosity results in increased surface roughness and decreased sphericity of the atomized droplets, along with a tendency for coarsening of primary Si. In the deposited state, TiB₂ acts as a heterogeneous nucleation core, which significantly promotes the nucleation of primary Si by providing effective nucleation sites. The refinement effect is enhanced with the increase of TiB₂ content: at 5 wt% TiB₂, the average size of primary Si is reduced to 4.74μm, while simultaneously the material density decreases to 2.31 g/cm³ and the porosity increases to 14.2%. Furthermore, TiB₂ forms semi-coherent interfaces with α-Al and primary Si, with mismatch degrees of 5.79% and 12.58%, respectively. The θ-Al 2 Cu phase also forms a semi-coherent interface with primary Si, with a mismatch degree of 15.15%. The semi-coherent interfaces formed by TiB₂ particles provide favorable lattice matching for Si nucleation, thereby refining the grains by lowering the nucleation barrier and restricting their growth. This constitutes the primary microscopic mechanism of grain refinement.