Surface topography changes in aluminum alloy sheet during large plastic straining under cyclic pure bending

• Published in: Journal of materials processing technology Vol. 213; no. 2; pp. 300 - 307
• Main Authors: Lucachick, Glenn A., Sanchez, L. Rafael
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.02.2013
• Subjects: Aluminum alloy AA 6022; Aluminum base alloys; Drawbeads; Electro discharge texture (EDT); Mill finish (MF) texture; Plastic deformation; Pure bending; Sheet metal; Strain; Surface layer; Surface roughness; Surface roughness average; Texture; Topography; Mill finish (MF) texture; Aluminum alloy AA 6022; Sheet metal; Surface roughness average; Drawbeads; Pure bending; Electro discharge texture (EDT)
• ISSN: 0924-0136
• DOI: 10.1016/j.jmatprotec.2012.09.011

► We study aluminum alloy sheet roughness changes under uniaxial, cyclic pure bending. ► We measure the three-dimensional surface roughness average and normalized volume. ► We determine significant effects under tensile-compressive substrate strains. ► We report differences between two common textures along two test directions. ► Results impact further modeling of tool radii contact and friction. This study consists of the experimental assessment of the surface topography of aluminum alloy AA 6022 sheet during large cyclic tensile and compressive plastic straining such as those present in the flow through drawbeads and small corner radii. Uniaxial and cyclic bending tests were used to measure the effects of such strains on the substrate layers of the sheet. All testing was performed without tool contact to ensure surface roughness changes were exclusively the result of the straining evolution of the free outer layers. The three-dimensional average surface roughness (Sa) was measured using optical interferometry. Changes in Sa were evaluated for two sheet textures: mill finish (MF) and electro discharge texture (EDT), along longitudinal and transverse rolling directions. Texture pattern, test direction, and bending/unbending strain are all shown to be significant contributors to variations in Sa. The magnitude of the initial surface roughness was also an important factor of the resultant %Sa variation, ranging from 40% ΔSa for EDT, to approximately 350% ΔSa for MF. Unbending the sample to its flat state considerably altered the Sa, disturbing any monotonic Sa trend. This made it unfeasible to assess the effects of strain history on a formed part based only on Sa values. The non-linear relationship between Sa and strain was more significant at medium and large strains. Effects on Sa due to bending/unbending of the substrate layer presented in this study must be taken into account in the modeling of more complex phenomena involving tool radii contact and friction.