The ubiquitous Beilby layer on aluminium surfaces

In 1996, it was found that the Beilby layer on rolled aluminium sheet could be imaged in the transmission electron microscope (TEM) on ultramicrotomed cross sections of the sheet surface. Following from this observation, we have examined Beilby layers on all types of aluminium surfaces that have been subject to high shear processing treatments such as rolling, grinding or machining. The layers are microcrystalline rather than amorphous, and they strongly influence properties like corrosion resistance and reflectance. Preferential precipitation in these deformed surface layers results in their electrochemical activation and it is responsible for the development of underfilm corrosion in most architectural and automotive alloys. More recently, it has been possible to directly image Beilby layers on ultramicrotomed stubs using the new generation of low kilovoltage high-resolution scanning electron microscopes and to carry out high-resolution TEM of sections cut from precisely located surface features. The paper presents an overview of all the recent investigations of high shear induced Beilby layers on aluminium alloys and discusses their control of surface properties. Copyright (C) 2010 John Wiley & Sons, Ltd.