Quantification of Deformation-induced Surface Roughening Using Modified Roughness Parameters and Fourier Filtering

Surfaces of metal sheets initially contain high frequency, low amplitude roughness components imparted during the rolling process. When plastic deformation is imposed, the amplitude of these free surface components increases, producing various kinds of morphological features including randomness, periodicity and waviness. The features often control key functional aspects of a metal surface, such as reflected image clarity, lubricant transport, and spot weldability. The key to understanding the evolution of topographical features on plastically deformed sheet surfaces involves characterizing those features using appropriate quantitative measures. In this study, selected roughness characterization tools are used to 3-D surface roughening of 6022-T4 Al sheets deformed in plane strain. Modified roughness parameters, viz., peak-to-valley mean-height roughness (Rmh) and 10% mean-height roughness (Rpv), were used to characterize roughness amplitude in order to overcome the deficiencies inherent with the root mean square roughness (Rq). A new approach, in which the roughness pattern is divided into several regimes, was also used to investigate the frequency components that provide the major contributions to surface roughening. The Fast Fourier Transform (FFT) algorithm was used to filter 3-D roughness into these different roughness regimes.