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Ternary Ni-Co-P/TiN(20 nm)nano-composite coatings with cobalt content in the range of 0~23 wt.% were successfully co-deposited on aluminum alloys by electroless plating.The morphology,composition,microstructure,microhardness,wear behavior and corrosion properties of the deposits were observed using SEM,EDS,XRD,Vickers hardness,ball-on-disc wear tester and electrochemical workstation,respectively.The effect of cobalt content on the tribological and corrosion properties of Ni-Co-P/TiN coatings was investigated.It is found that all the nanocomposite coatings have a compact and rough granular structure with sub-micro globules nonuniformly distributed on the surface.The grain size and the content of Ni and P decrease,but the micro-hardness,adhesion force,friction coefficient and corrosion resistance correspondingly enhance with the increase of cobalt content in Ni-Co-P/TiN coatings.It is revealed that the improved corrosion resistance of Ni-Co-P/TiN nanocomposites is ascribed to the passivation behavior and small grain caused by the introduction of cobalt.Based on the excellent performance on the wear resistance and corrosion resistance,ternary Ni-Co-P/TiN nano-composite coatings with high Co content,such as Ni-Co22.93-P/TiN,may be applied as a wonderful protective coating for Al alloys.