Abstract: In this study, aluminum matrix composites (AMCs) reinforced with dual-phase TiN and AlN particles were fabricated by laser powder bed fusion (LPBF), aiming to form a Ti_1-xAl_xN solid solution through in-situ reactions for synergistic strengthening. To further enhance this synergistic effect, a method combining collective high-energy ball milling to activate the reinforcement particles prior to LPBF (collectively mixed dual-phase, CD-AMC) was developed and compared with directly mixed (DD-AMC) and separately refined (SD-AMC) approaches. The ceramic particles undergo significant refinement after high-energy ball milling, which enhances the laser absorptivity of the composite powder and further increases the melt pool temperature during LPBF processing. The as-built composites exhibit novel microstructure attributed to the incorporation of dual-phase reinforcements, including a gradient layer on the reinforcement surface, nanoparticle precipitates, and bimodal grain structure. The multi-level microstructure formed through in-situ reactions extends beyond conventional simple phase superposition and leads to an inherent reinforcement effect. The reinforcements subjected to collective high-energy ball milling promote reinforcement-induced microstructural evolution, leading to enhanced mechanical properties, with tensile strength improvements of approximately 26.0 % and 8.3 % over DD-AMC and SD-AMC, respectively. The mechanical strength enhancement mechanism can be attributed to improved load transfer, finer grains, and an increased amount of nanoprecipitates.

Key words: Laser powder bed fusion, Aluminum matrix composites, Synergistic strengthening, In-situ reaction