Ni-Co-P/nano-sized Si 3 N 4 composite coating was successfully fabricated on aluminum alloys by electroless plating in this work. The surface and cross-sectional morphologies, composition, microstructure, microhardness, friction and wear behavior of deposits were investigated with SEM, EDS, XRD, Vickers hardness and high-speed reciprocating friction, respectively. It was found that a Ni-Co-P/nano-sized Si 3 N 4 composite coating on aluminum alloy substrate is uniform and compact. The existence of nano-sized Si 3 N 4 particles in the Ni-Co-P alloy matrix causes a rougher surface with a granular appearance, and increases the microhardness but decreases the friction coefficients and wear rate of electroless coatings. Meanwhile, the effects of heat treatment at 200, 300, 400 and 500 C for 1 h on the hardness and tribological properties were researched. It is revealed that both of the microhardness and tribological properties of Ni-Co-P coatings and Ni-Co-P/Si 3 N 4 composite coatings increase with the increase of heating temperature in the range of 200-400 C, but show different behavior for the two coatings after annealing at 500 C.

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