A series of nano-WC surface modified AlSi10Mg powders with different WC contents were synthesized by the electrostatic assembly method. After the selective laser melting (SLM) processing, various Al-W intermetallics were in-situ formed in the SLM nano-WC/AlSi10Mg composites. A well-coherent Al/Al₅W interface with a low lattice mismatch of 4.7% was confirmed with an orientation relationship of (002)_α(Al)//(104)_Al5W. The nano-WC particles and Al-W intermetallics triggered the columnar-to-equiaxed transition, leading to a fine equiaxed microstructure. As a result, the SLMed 3 wt.% nano-WC/AlSi10Mg composites showed remarkable mechanical properties, with an ultimate tensile strength of (464.1±8.68) MPa and elongation of (5.6±0.95)%. Additionally, the SLMed 3 wt.% WC/AlSi10Mg samples also achieved the lowest average coefficient of friction (0.429) and wear rate of 3.842×10^-5 mm³/(N·m) compared to other WC/AlSi10Mg composites. The remarkable mechanical and wear properties are ascribed to fine-grain and second-phase strengthening.