Effect of Working Voltage on the Microstructure and Comprehensive Properties of Electro-Brush-Plated Nickel–Graphene Composite Coatings

To improve the surface service durability and heat-transfer performance of brass heat-dissipation components, Ni–graphene (Ni–Gr) composite coatings were prepared on brass substrates by electro-brush plating, and the effects of working voltage on the coating microstructure and overall performance were investigated. The coating thickness ranged from 6.667 to 19.334 μm. The results show that the coating prepared at 7 V had a thickness of 8.524 μm, a dense microstructure, relatively uniform graphene dispersion, and the lowest Raman ID/IG ratio of 1.2146, thereby exhibiting the best overall performance. The microhardness of this coating reached 395 HV, which was approximately 190% and 127% higher than those of the brass substrate and pure Ni coating, respectively. Its corrosion current density in 3.5 wt.% NaCl solution decreased to 1.0143 × 10−5 A/cm2, corresponding to a 90.4% reduction relative to the pure Ni coating. The room-temperature thermal conductivity of the coating/brass composite specimen reached 145 W/(m·K), which was 29.5% higher than that of the brass substrate. When the working voltage increased to 9–11 V, although the coatings became thicker, surface nodules coarsened, pores/pinholes increased, and graphene agglomeration intensified, leading to declines in mechanical properties, corrosion resistance, and thermal conductivity. These results demonstrate that an appropriate working voltage is beneficial for coordinating Ni nucleation/growth and graphene co-deposition, and is a key processing parameter for obtaining high-performance Ni–Gr composite coatings for brass heat-dissipation components.