Directed energy deposition (DED) of aluminum with infrared lasers faces many processing issues, e.g., poor formability, pore formation, high reflectivity, all lowering the productivity. In this paper, we developed and applied a 2 kW high-power (450 nm) blue laser directed energy deposition (BL-DED) of a nano-TiB2 decorated AlSi10Mg composite. The single-track experiment reveals that the required power density of blue laser to form fully melted track is lower than that of an infrared laser (1060 nm). Under the laser power of 900 W with a scanning speed of 4 mm/s, the width and depth of molten pool is approximately 2500 µm and 350 µm respectively with blue laser, while the powders are not fully melted with infrared laser, owing to aluminum's higher absorption at blue laser wavelengths. The area fraction of equiaxed grains accounts for as high as 63% at 4 mm/s. To the best of our knowledge, this result is the highest area fraction of equiaxed grains in a single-track molten pool of DED process. Such a high fraction is mainly due to the low thermal gradient (8 × 105 K/m) of the flat-top blue laser and the refining effect of nano TiB2 particles. Our work demonstrates that high-power blue laser has enhanced both efficiency and build quality compared to DED of aluminum alloys and composites using an infrared laser, which also promises to help process other high-reflectivity materials like copper alloys
