Methodology for quantification of the roping phenomena in 6xxx automotive car body sheet alloys

摘要

An important aspect when Al sheets are to be used for visible outer car body panels is surface appearance. Some age-hardenable Al-Mg-Si alloys can suffer from a phenomenon called roping. Roping appears on a macroscopic scale and manifests itself as the development of ridges and valleys 90° to the original rolling direction with a wavelength ranging from 1 to 10 mm during forming. However, the extent of roping, and therewith the judgment of the quality of the surface appearance has up to now been done mostly on a qualitative basis. Hence, the goal of such a so far not established methodology is to be able to quantify the extent of roping and to correlate it to a visual appearance ranking of roping. In the present study, a novel combination of a characterisation technique with an evaluation method is used to characterize and evaluate the roping behaviour in aluminium alloys. This approach combines these already individually existing methods to a powerful tool: the measurement of a 3D surface topography with a subsequent analysis by means of Fourier analysis. Various car body sheet grades were analyzed by means of this technique.