Surface nanocrystallization of Al-plated steel for application in the exhaust system of vehicles

Aluminum-plated or aluminized steel has been used in the exhaust system of vehicles, which exhibits a reasonably high corrosion resistance in the exhaust gas condensate environment. However, due to the inhomogeneous element distribution the outmost surface layer, which is directly exposed to the exhaust gas, is more like an aluminum layer (with little intermetallic compounds) that, though corrosion-resistant, may not be strong enough to effectively resist erosion. In this work, efforts were made to increase the service life of Al-plated or aluminized steel surface, particularly to enhance the outmost surface layer by nanocrystallization for improved resistances to corrosion, wear and corrosive wear. The entire process includes dipping steel specimens into a molten Al pool to make an Al coat, sandblasting the surface coat to generate dislocation network or cells, and recovery treatment to turn the dislocation cells into nano-sized grains. Electrochemical properties, electron work function (EWF), wear and corrosive wear of the nanocrystalline surfaces were investigated. It was demonstrated that the nanocrystalline aluminized surface exhibited improved resistances to corrosion, wear and corrosive wear.