Papers by Keyword: Roping

Abstract: AA6xxx alloys are known to suffer from a phenomenon called roping, which is a ridge and valley pattern appearing after stamping is treated as a fatal surface defect for the automotive skin panels. Although the roping is the important factor to determine the exterior quality, it is commonly evaluated by visual check done by inspecting staff, which is very subjective and difficult to measure quantitatively. In this study, to quantify the roping level in detail and easily, a new calculation method based on Fourier transform and using simple device to measure topography is proposed. As a result of analyses for several different AA6022 alloy sheets, it is found that the strong roping surface has the intensive directional pattern along the rolling direction with a specific wavelength. The roping level can be expressed numerically as the ratio between the amplitude of the rolling directional pattern and the average amplitude of each directional pattern. This value shows good agreement with the roping level determined by human observation. Moreover, it is found that the proposed method can be applied to the surface appearance obtained by digital camera without a 3D profiler.

Abstract: 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 of the AA 6xxx series 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 when the sheet is formed to typical parts like doors or hoods. In the past years Al industry has developed means to minimise roping by careful control of alloy composition and through appropriate thermo-mechanical processing schedule. The increasing use of aluminium for outer skin applications gives proof that these efforts were successful. However, the extent of roping, and further the judgment of the quality of the surface appearance has up to now been done on a qualitative basis with comparisons against reference samples, as there are no established experimental techniques and no established analysis procedures for the quantification of this phenomenon. The goal of such a methodology is to be able to quantify the extent of roping in 6xxx automotive car body sheet alloys 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 behavior in aluminum 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. The analysis of various car body sheet grades by means of this technique for uniaxial and biaxial loading conditions is presented in this paper.

Abstract: Recrystallization was investigated in the context of its effect on the roping phenomenon in a 6000 series Al alloy. The findings suggest that, in general, the recrystallized grain size affects the material's susceptibility to roping more than the actual area fraction of specific texture components. For example, bands of Cube grains were typically observed in the final processed samples in cases which had coarse, recrystallized grain sizes from the earlier stages of processing. In contrast, bands were not observed for cases having fine, intermediate recrystallized grain sizes. Although microstructure and texture are highly intertwined, these findings suggest that the microstructural characteristics, such as the recrystallized grain size, are more important than those related to the texture.

Abstract: The through-thickness textures of different variants of AA6111 T4 sheets were investigated by using X-ray pole figure technique, scanning electron microscopy (SEM), and electron back scattering diffraction (EBSD) technique in SEM. The roping behaviors of the sheets were determined and corelated to the through-thickness texture inhomogeneity. It has been demonstrated that (i) roping is due to through-thickness texture inhomogeneity, (ii) roping occurs in AA6111 when the cube and Goss texture components segregate along the rolling direction (RD) and alternate in the transverse direction (TD), (iii) the texture alignment from sheet surface to 1/5 thickness is most critical to roping behavior, while the effect of texture in the sheet centre is masked by the surface layer, and (iv) the texture alignment can be attributed to the stability of cube and Goss in rolling, and the nucleation and grain growth advantage of cube and Goss during heat treatments.

Abstract: Aluminium alloys for car body manufacturing often show a specific type of band-shaped surface roughening upon stretching, called “ridging” or “roping”. Experimental research as well as modelling attempts have indicated that the evolving surface roughness profiles cannot be understood based on banding of individual surface texture components, like cube or Goss, only. Therefore, it is proposed to study banding on the “mesoscopic” level of texture banding rather than on the “microscopic” one of orientation banding. In mechanical terms, such patterning in the texture would lead to patterning in, for instance, the Lankford coefficient (r-value), so that the mechanical response can be calculated on an intermediate length scale. The present contribution presents a method for calculating r-value patterning from Electron Backscatter diffraction (EBSD) orientation maps. In a first test case of a strongly ridging AA6xxx sheet, indeed patterning in the r-value is found which corresponds to reported patterning of the surface roughness.

Abstract: The effect of two different intermediate annealing (IA) treatments on texture banding in a roping prone aluminium alloy was investigated. It was found that texture banding occurred in the final annealed material that underwent an IA treatment consisting of slow heating in which there was significant interaction between the recrystallizing grains and the particles in the material. A more uniform distribution of orientations in the final annealed material was obtained in the case of an IA treatment with fast heating so that there was no significant effect of particles on recrystallization.

Abstract: Roping was investigated in two 6016 aluminium alloys that exhibit different levels of susceptibility to its occurrence. The level of roping is lower, as manifested by the less pronounced (roping) lines on the surface, in the GR material compared to the BR case. Through-process characterization of GR and BR materials by means of electron backscatter diffraction (EBSD) reveals similarities in the grain size, (grain) orientation texture and the spatial distribution of {100} <001> Cube grains up to, but not including the T4 state. Cube grains in the T4 state are spatially banded in the BR material but more uniformly distributed in the GR case. It was found that the thermo-mechanical treatments prior to the T4 state account for the difference in spatial distributions of Cube grains and hence, the different roping behaviours exhibited by these materials.

Abstract: In this work we present deformation experiments of polymer-coated polycrystalline aluminium sheets. We observe that the straining is accompanied by the development of microstructural defects at the sample surface as well as in the interface between the metal and the different polymers. These defects are due to a variety of dynamical mechanisms which are essentially induced by bulk plasticity of the metal substrate. They micromechanically interact with the polymer coating and transfer some of the metallic roughness to the coating and to the surface.