Low-Pressure Cold Spraying of Copper–Graphite Solid Lubricating Coatings on Aluminum Alloy 7075-T651

Although aluminum alloy 7075-T651 is widely used in the automobile and aircraft manufacturing industries, its durability must often be increased by improving the surface properties of components to better resist wear and oxidation. We propose herein the deposition of copper–graphite solid lubricating coating on aluminum alloy 7075-T651 by using the low-pressure cold-spraying technique. The microstructure, deposition efficiency, mechanical properties, and dry sliding wear behavior of the copper–graphite coatings were investigated. The results showed that addition of Cu-coated graphite particles could decrease the plastic deformation of adjacent copper particles in the coatings. The deposition efficiency, hardness, and bonding strength of the copper–graphite coatings decreased (by 49%, 21%, and 70%, respectively) with an increase in the Cu-coated graphite content in the feedstock from 0 to 20 wt.%. The copper–graphite coating with Cu-coated graphite content of 20 wt.% showed the lowest friction coefficient (about 0.15) and wear rate (6.00 × 10⁻⁵ mm³/N m). Compared with aluminum alloy 7075-T651, the friction coefficient and wear rate were decreased by 57% and 78%, respectively, which can mainly be ascribed to the formation of a low-shear-strength graphite-rich solid lubricating film on the worn surface. When the Cu-coated graphite content exceeded 10 wt.%, the dominant wear mechanism changed to mild abrasive wear, in contrast to the oxidative wear of the pure copper coating.