Steel coating application for engine block bores by Plasma Transferred Wire Arc spraying process

• PTWA spraying process is applied to engine cylinder bore coat.
• The steel coating composition is reproducible with regard to oxides and pores.
• The tribological behavior of PTWA coating is better than conventional cast iron liner.
• Bore surface defects and bore top/upper parts protection have to be controlled.

Thermal spraying development for automotive industry grows since the end of the nineteen nineties. In the case of engine blocks, bores were before plated by a chemical process or liners were inserted in cylinders to ensure the tribological performances. In fact, aluminum has poor wear properties. Nowadays, a lot of research is conducted on the reduction of weight by liner replacement. The main solution is the coating application directly on the aluminum cylinder bore. In this way, weight is reduced and design can be improved to furthermore develop performance and efficiency. Different processes are employed such as plasma, HVOF or electrical arc. One of them is the Plasma Transferred Wire Arc spraying (PTWA) consisting of a plasma jet formed by a transferred arc between a cathode and a wire. Its tip is melted and blown by a gas blast toward the bore surface. This paper presents the PTWA process applied for cylinder bore coating. Typical coating is presented in terms of composition with two arc current intensities used. Tribological tests measurements were done and compared to the previous solution consisting of cast iron liner. Some technical and problematic points are presented around the spraying process in bores.