Friction Reduction by Laser Irradiation for a Friction System Using Bearing Steel and Aluminum Alloy in Engine Oil

Aluminum alloy sliding components are widely used in internal combustion engines. However, aluminum easily adheres to the countersurface, resulting high friction. Hence, laser irradiation was oxidize surface and promote tribofilm formation using molybdenum dithiocarbamate zinc dialkyldithiophosphate (ZnDTP). This study investigated reduce friction between steel balls disks fully formulated engine oil. Laser scanning create 100-μm-pitch concentric circles on disks. The behavior classified into two modes: no reduction (mode-I, μ: 0.09–0.12) after high-friction period (mode-II, 0.06–0.09). Friction mode transition occurred when energy density exceeded critical value (Ec). Energy-dispersive X-ray spectroscopy photoelectron showed that, for mode-I, adhered ball, sulfur-containing formed. For mode-II, ZnDTP-derived phosphate film formed disk suppressed adhesion, a ball. Micro-Vickers tests diffraction that an amorphous/nanocrystalline structure unirradiated area owing heat diffusion under high-energy-density (>Ec). Results suggest metallographic structural change promotes ZnDTP reactions, causing transition.