Scuffing resistance of coated piston skirts run against cylinder bores

Piston skirt/cylinder bore scuffing is one of the main failure mechanisms that affect the life of automotive engines. The purpose of this research is to study hot scuffing and wear resistance of piston skirts with different surface textures and coatings running against cylinder bores using an apparatus which can simulate the relative motion between the piston and cylinder bore. The experimental studies involve three skirt coatings with two different skirt surface textures running against bore surfaces made of three different aluminum alloys and cast iron. In addition to the scuffing performance, this work also analyzes the microstructure and morphology features of the surfaces and the sub-surfaces of the pistons and cylinder bores. The results indicate that scuffing resistance of different aluminum alloy cylinder bore and piston skirt combinations varies significantly. The eutectic Al–Si alloy with high percentages of alloying elements has better scuffing resistance than the hypereutectic Al–Si alloys. The scuffing resistance is also affected by casting porosity on the bore surface. Ni–P–BN plated and iron plated pistons perform very well with aluminum bores. Surface contact, mechanical and chemical properties of bore materials, piston skirt surface textures and coatings are the major factors affecting the scuffing resistance.