Microstructure evolution and mechanical properties strengthening in laser powder bed fusion of high-strength SiC and TiB2 co-reinforced Al-Zn-Mg-Cu composites

A SiC and TiB2 particles reinforced Al-Zn-Mg-Cu matrix composite was designed and fabricated using laser powder bed fusion (LPBF). This study investigated the effects of ceramic reinforcements on the phase composition, microstructures, grain crystallization, and mechanical properties. The mechanisms of microstructure evolution and mechanical strengthening were discussed. Results show that a multi-level microstructure with ceramic reinforcements and nanoprecipitates has been developed. The ceramic reinforcements exhibited a uniform distribution within the matrix, while the eutectic precipitates formed a network substructure along the grain boundaries. A novel interfacial bonding mechanism, SiC/Al4C3+eutectics/Al, has been developed through an in-situ reaction between SiC and Al. Ceramic reinforcements provided sufficient nucleation sites for grain nucleation, transforming from coarse columnar growing along the [001] direction parallel to the printing direction to fined equiaxed grains with random growth. The mechanical properties were enhanced, and the microhardness heterogeneity along different directions was reduced. The ultimate tensile strength and elongation were 516±12 MPa and 6.12±0.36 %, respectively. The enhancement of mechanical properties was attributed to superior interfacial bonding strength, fine grain strengthening, solution strengthening, second phase strengthening, and substructural strengthening. This work could demonstrate the potential for fabricating AMCs using LPBF with Al-Zn-Mg-Cu alloy as the matrix.