Laser powder bed fused pre-alloyed TiB₂/Al-Si composite: In-situ tailoring of microstructure and mechanical properties by substrate preheating

Compared with other particle-reinforced aluminum matrix composite, the laser powder bed fused (LPBF-ed) pre-alloyed TiB₂/Al-Si composite exhibit an excellent combination of mechanical properties, offering great potential for producing critical and complex aerospace components. However, their practical application often requires post-process heat treatments to refine microstructure, which increases cost and complexity and contradicts the current pursuit of low CO₂-footprint and green manufacturing. In this study, the in-situ tailoring of the microstructure and mechanical properties in LPBF-ed pre-alloyed TiB₂/Al-Si composite was investigated by varying the preheating temperature (80 °C, 120 °C, 160 °C, and 200 °C). All specimens exhibited low porosity (<0.3 %). Microstructural analysis revealed that increasing the preheating temperature coarsened the net-shaped Al-Si eutectic, induced fragmentation and spheroidization of the net-shaped Al-Si eutectic, and promoted the precipitation of nano-sized Si particles. Moreover, preheating reduced the thermal gradient, facilitating the formation of more equiaxed grains. The mechanical properties showed a non-monotonic dependence on preheating temperature. At 160 °C preheating, the composite exhibited optimal performance, with tensile strength of 474.51 MPa, yield strength of 353.51 MPa, and total elongation of 9.71 %. This improvement arose from enhanced precipitation strengthening, whereas excessive preheating (200 °C) caused precipitate coarsening and eutectic degradation, leading to strength deterioration. This work demonstrates that controlled preheating provides an effective in-situ strategy to tailor the microstructure and achieve a superior strength–ductility synergy in LPBF-ed pre-alloyed TiB₂/Al-Si composite, offering a viable pathway for manufacturing high-performance aluminum components.