Next-gen composite sheets: Experimental and numerical investigation of processing and solidification kinetics of continuously cast Al-12Si-(TiB2 + Al2O3) hybrid composite

Abstract

The demand for Al-Si-based composites in automotive industry has driven the development of near-net shape continuously cast sheets. Conventional route of fabricating composite sheets required enormous amount of energy during the secondary processes. Therefore, the present study focuses on fabricating a 3 mm thick in-situ Al-12Si-12.5(TiB₂ + Al₂O₃) hybrid composite sheet using vertical twin-roll continuous casting (VTRC) and comparing it to 6 mm thick gravity die-casted component. The investigation involves numerical and experimental methods to understand solidification kinetics and microstructure evolution during the processing of hybrid composite sheets. The numerical study involves the multiphysics of fluid flow and heat transfer with variable viscosity and solid fraction with temperature within a three-dimensional melt pool, which promotes formation of recirculation zones and promotes homogeneous temperature distribution. While processing, the reinforcement particles inside aluminium melt were synthesized using an in-situ metal-salt reaction method at 1053 K. The processing temperature for VTRC sheet was 910 K, determined using a dendritic coherency-based solidification criterion. The composite sheet characterization showed the presence of α-Al, acicular Si, and Al₂O₃ particles along with TiB₂ particles in the microstructure. The average grain size (43.32 μm) and TiB₂ particle size (0.90 μm) in the sheet was greater than in the gravity die-cast component (35.93 and 0.59 μm) despite higher solidification rates (8.77 K/s) in the sheet. This was attributed to longer nucleation and recalescence undercooling during sheet fabrication. The composite sheet exhibited 34.3 % increase in Vickers microhardness compared to Al-12Si base alloy and an ultimate tensile strength of 218.64 MPa.