Plasma Nitriding of Spray-Formed Aluminum Alloys

Engine components in motor vehicles are subjected to permanently increasing mechanical, tribological, and corrosive stresses. Due to the insolubility of nitrogen in Al, the nitriding process is carried out as external nitriding by the diffusion of Al atoms towards the surface which is contrary to the mechanism observed for iron based materials. In cases of external loading the thin AlN layer is not supported by the soft Al substrate and although the AlN coating layer is many times harder than the base Al material, it can easily break if high loads are applied which is called the 'egg-shell' effect. The microstructure of the base materials, the nitride layer structure and the surface coverage with AlN were characterized by means of metallographic cross-sections and fractured specimens using optical and scanning electron microscopy.