Advanced Hypersonic Flamespray Coatings for Cylinder Liners in Light Metal Engines

The reduction of fuel consumption and pollution emissions, the improvement of the engine efficiency as well as the cost reduction in manufacturing and assembly are in the focus of actual research activities in the automotive industry. Most of these requirements can be fulfilled by a reduction of the total vehicle weight. This results in an increasing utilization of light metals for chassis, body and engine components. Significant weight savings are obtained by changing the engine block material from cast iron to aluminum. Due to the harsh operation conditions, the aluminum cylinder must be reinforced. Approaches to increase combustion as well as operation efficiency and lifetime of light metal engines are thermally sprayed APS (Atmospheric Plasma Spraying) and HVOF (High Velocity Oxygen Fuel Spraying) coatings on cylinder liners of the aluminum crankcases. By using this coating technologies, also material combinations containing solid lubricant dispersions can be deposited. The thermal spray processes represent a cost effective and flexible solution for the engine technology. Meanwhile, APS coatings for 4-cylinder engine blocks are produced in series production. Actual research activities are focused on the development of advanced HVOF sprayed coating systems on cylinder liners, the coating optimization and the cost effective implementation of this technology in an automated series production process.

In hypersonic flame spraying (HVOF), the coating is deposited by an elliptically moving HVOF gun, whereas the cylinder liner is rotating. By HVOF processing an improved coating microstructure (less porosity) and superior coating adhesion is obtained. The HVOF coatings are homogeneous, with a dense, bulk like microstructure, a low porosity (« 5%) and surface roughness as well as a superior coating adhesion compared to APS coatings.