Characterization and mechanisms of formation of disturbed layer during rolling of aluminium alloys

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Aluminum sheets experience high compressive and shear stresses as well as high temperature during hot rolling. These severe conditions alter the local composition and microstructure of the surface by formation of localized layers known as "disturbed layer". The formation of disturbed layer changes the appearance (colour), tribological behaviour, weldability, surface tension, and corrosion resistance of aluminum roll-products. The project aims to improve our understanding of the tribological factors that affect formation of the disturbed surface layer during aluminum rolling using a custom made rolling simulator at the University of Windsor. The disturbed layer is speculated to form mostly during hot rolling process, where the sheet enters to the roll gap at a temperature range of 340C - 550C. Due to sliding friction between the rolls and the sheet surfaces, the speed of the sheet at the exit side of the tandem mills is normally higher than the linear speed of the rolls (forward speed). Due to forward speed, the rolls slide against aluminum sheet surfaces causing localized shear deformation on surface of aluminum sheet mixed with lubricant residues and surface oxides forming the disturbed layer. The proposed research will be conducted by i) in depth microstructural and chemical analyses of surfaces and subsurfaces of the aluminum samples and the steel rolls before and after rolling experiments ii) determining the mechanisms of formation of disturbed layer under various rolling conditions and iii) construction of maps that show the thickness, morphology, composition, and structure of the disturbed layer as functions of rolling parameters. These results will provide significant environmental and economic benefits, including lower energy consumption to produce final products, less re-work, and lower consumption of cleaning chemicals for removal of the layer, and higher quality products.