Friction, wear, and anti-scuffing behaviors of zinc phosphate film on cylinder liners

Zinc phosphate chemical conversion coating possesses excellent tribological properties, which has attracted increasing attention. In this work, the friction, wear and anti-scuffing performance of zinc phosphate film applied on the cylinder liners were studied using a self-designed friction and wear experimental apparatus, which can sufficiently simulate the working conditions of the piston ring and cylinder in a real engine. The experimental results indicate that comparing with the uncoated cylinder liner, the friction force and total wear losses of friction pairs for the zinc phosphate coating are reduced by 8% and 27.5%, respectively, which is attributed to the formation of the protective film containing metal oxides and iron phosphate. In the scuffing test, uncoated cylinder liner exhibits better anti-scuffing performance because of the spalling of the cast iron graphite. On the contrary, the zinc phosphate coating particles remaining on the worn surface after oil-cut off are peeled off and acted as the abrasive at the contact interface, which accelerates the plastic deformation of friction pairs and the cast iron graphite is covered by the plastic flow of the material.