Finite element simulation of extremely high shear strain during a single-pass asymmetric warm rolling of Al-6.2Mg-0.7Mn alloy sheets

摘要

Shear strain and accumulated strain plays a critical role in the grain refinement of aluminium alloys processed by asymmetric rolling, when circumferential speeds of the top and bottom rolls are different. Asymmetric rolling induces larger grain refinement in the mode of severe plastic deformation, when accumulated strain with dominant shear strain is more than 3. Searching the optimal process parameters which provide such extremely high deformation characteristics is very important. This paper presents the distributions of the accumulated strain through strip thickness of Al-6.2Mg-0.7Mn alloy processed by a single-pass asymmetric warm rolling. Effects of thickness reduction per pass (10...60%), rolls speed ratio (1...60%), diameters of the rolls (50...500 mm), contact friction coefficient (0.1...0.4), initial strip thickness (1...8 mm) and ratio of contact arc length to average thickness of strip were investigated by the rigid-plastic finite-element analysis with taking into account the heat generation due to work of plastic deformation and friction. The non-linear effect of rolls speed ratio on the deformation characteristics during asymmetric warm rolling was found. Extremely high shear strain and accumulated strain up to e=3.8...4.8 were reached during a single-pass asymmetric warm rolling. Finite element analysis of the deformation characteristics, presented in this study, can be used for optimization of the asymmetric rolling process as a method of severe plastic deformation.