Self-Lubricating Graphene Nanoplatelet Coatings on Aluminum: Effect of Surface Pretreatment on Tribological Performance via Electrophoretic Deposition

Aluminum plays a key role in modern industry because of its lightweight and remarkable recyclability. On the other hand, aluminum exhibits weak wear resistance and high coefficient of friction, limiting its use in heavy duty applications. This work presents a comprehensive investigation into the fabrication and tribological evaluation of graphene nanoplatelets (GNPs) coatings on aluminum substrates using the electrophoretic deposition (EPD) technique. Putting emphasis on the critical influence of substrate pretreatment, the study systematically explores acid, alkaline, and combined acid-alkaline etching protocols to optimize coating morphology, adhesion, and performance. The results reveal that combined pretreatments, particularly the sequential application of NaOH followed by HCl, significantly enhance surface roughness and wettability, thereby facilitating the formation of thicker, more uniform and highly adherent graphene coatings. Tribological testing demonstrates a remarkable reduction in friction coefficients (below 0.25) and wear volumes (up to 99% lower) for GNPs-coated samples compared to bare aluminum, with the most durable and low-friction coatings achieved on substrates subjected to combined pretreatment. Notably, the NaOH-HCl sequence yields coatings with the highest adhesion and service life (over 400 meters of sliding), underscoring the synergistic effect of sequential oxide and hydroxide removal on coating performance. Compared to more complex and expensive methods such as chemical vapor deposition, the EPD approach offers a scalable, cost-effective solution compatible with aluminum substrates, delivering comparable or superior tribological properties. This study establishes a clear pathway for the development of robust self-lubricating graphene coatings tailored for lightweight, high-performance applications such as electrical contacts and bearings.