Anisotropy of Surface Roughness on Aluminium Sheet Studied by Atomic Force Microscopy

Abstract

Atomic force microscope images of aluminium sheet are used to calculate the mean roughness Ra andthe root mean square roughness Rq for different directions ([theta]) across the samples. The angle determined valuesof Ra([theta] and Rq([theta]) are significantly lower in the rolling direction than in any other direction. The resultsprovide a clear demonstration of the vector nature of surface roughness. Local features in an angle determinedRq([theta]) profile are also compared with the positions of peaks and valleys in the matching topographical crosssectionof the surface running at right angles to [theta]. It is further found that the distribution of z heights for animaged sample is usually not Gaussian in shape unless the z heights are measured about mean lines constructedacross the surface parallel with the rolling direction. The results are relevant for controlling lubricationperformance in the aluminium rolling process.