Tenfold Enhancement of Wear Resistance by Electrosynthesis of a Nanostructured Self-Lubricating Al2O3/Sn(S)?MoS2 Composite Film on Al?Si?Cu Casting Alloys

Enhancing tribological performance through nanostructure control is crucial for saving energy and improving wear resistance for diverse applications. We introduce a new electrochemical approach that integrates aluminum (Al) anodization, tin alternating current (AC) electrodeposition, and anodic MoS₂ electrosynthesis for fabricating nanostructured Al₂O₃/Sn(S)MoS₂ composite films on AlSiCu casting alloys. Our unique process uses Sn-modified MoS₂ deposition to form robust solid lubricant MoS₂–SnS electrodeposits within the nanochannels and microsized voids/defects of anodic alumina matrix films on the base materials, resulting in a bilayered Al₂O₃/SnSMoS₂ and MoS₂–SnS–Sn composite film. The AC-deposited Sn enhances conductivity in the anodic alumina matrix film, acts as catalytic nuclei for Sn@SnS@MoS₂ core-shell nanoparticles and a dense top layer, and serves as a reductant for the direct synthesis of hybrid solid lubricant MoS₂–SnS from MoS₃ by anodic electrolysis of MoS₄²⁻ ions. The resulting nanocomposite film provides a two-fold increase in lubricity (friction coefficient (COF) μ = 0.14 ⇒ 0.07) and a ten-fold improvement in wear resistance (COF μ < 0.2) compared to conventional Al₂O₃/MoS₂ film formed by anodizing and reanodizing. The effectiveness of the Al₂O₃/Sn(S)MoS₂ composite is further validated through real automotive engine piston tests.