Abstract
Graphene nanosheets and Ni were used to develop oxide matrix composite coating on anodic hard coating (AHC). Anodized Al-6061-T6 alloy was Ni plated in a solution containing 50 mg l⁻¹ graphene nanosheets. The effect of plating time on the microstructure and properties of coatings was investigated. FE-SEM, EDS, and Raman spectroscopy were used to analyze the surface morphology, cross-section, and chemical composition of composite coatings. The presence of graphene seemed to result in the refinement of the Ni matrix grain structure. Vickers micro-hardness and dry sliding wear tests were conducted on the coatings. AHC + Ni/Gr showed 60 percent higher hardness than AHC + Ni coating (160 ± 34 HV). The presence of graphene in AHC + Ni/Gr coatings reduced the wear rate and average friction coefficient compared to AHC and AHC + Ni coatings. AHC + Ni/Gr obtained after 10 min electroplating presented the lowest wear rate. The dominant wear mechanism in AHC + Ni coating was fatigue wear, while AHC + Ni/Gr exhibited abrasion and delamination.

Key words
anodic hard coating, nickel precipitates, graphene nanosheets, composite coating, friction coefficient

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