Finite Element Simulations Of Asymmetric Rolling Of AA7050Aluminum Alloy

Abstract:High-strength and high-toughness aluminum alloys are very important structural materials. They have been widely used in many vital areas, such as the aerospace and aviation, because of their optimum overall performance. Asymmetric rolling is expected to improve performance of Al plate as it can introduce severe plastic deformation. The limited literature shows that snake rolling can significantly improve the mechanical properties of Al alloy plates, especially in the center layer of its thickness. Conducting research on snake rolling can provide a reference for aluminum alloy plate processing technology to obtain plates with relatively uniform properties that could not be obtained by conventional rolling.This research is supported by the "Basic research for aviation high-performance aluminum alloy" project in the National Key Basic Research and Development Program of China. In this study, finite element method (FEM) is employed to investigate the bending behavior, contact deformation zone and the through-thickness distribution of strains in, as well as the rolling forces during asynchronous rolling, horizontally-displaced rolling and snake rolling of an AA7050alloy. The results of asymmetric rolling are compared with those of conventional rolling. The reliability of the FEM results is verified through comparing with the experiments. The main results can be summarized as follows:(1) In asynchronous rolling with rolls having different diameters, the curvature of rolled plate changes significantly with the rolling reduction and there are considerable effects of the velocity ratio. The width of the cross shear region (CSR) improves with the increasing roll diameter ratio, and decreases first and then increases with the increasing reduction. Asymmetrical rolling can improve the uniformity of the through-thickness deformation in rolled plates, and reduce the rolling forces when the diameter ratio is greater than a certain value, with respect to the symmetrical rolling.(2) In horizontally-displaced rolling, both the initial plate thickness and the reduction affect the rolled plate curvature. The plate bending direction may change at some reductions when the reduction changes in a certain range. The greater the initial plat thickness is, the less times the bending direction changes. The CSR width decreases to zero first and then improves with increasing reduction, and the directions of the contact shear stresses on the lower and upper surfaces in the CSR exchange at the reduction when the width of the CSR equals to zero. When the rolling reduction keeps unchanged, the CSR moves to the rolling direction with the increasing initial plate thickness, resulting in a greater proportion of backward slip zone. The horizontally-displaced rolling can improve the uniformity of the through-thickness shear strain and equivalent strain in rolled plate, but raise the rolling force of the upper roll.(3) In snake rolling with rolls having different diameters and horizontally-displacement, when the diameter ratio is a constant, it is difficult to get flat rolled plates by adjusting the horizontal-displacement at some reduction. At other reductions, flat plates can be obtained but the corresponding horizontal-displacements are in a small amount. When the horizontal-displacement is fixed and the diameter ratio is changed, the bending direction only changes at some reduction. As diameter ratio changes, the change of the CSR is similar to that in asynchronous rolling. As reduction changes, the change of the CSR is similar to the horizontally-displaced rolling. Snake rolling can effectively improve the proportion of shear deformation and uniformity of the through-thickness distribution of the sheer strain, but has no effect on the through-thickness distribution of the normal strain along the rolling direction and the equivalent strain.(4) Average values of the through-thickness equivalent strain in the plates processed by asynchronous rolling, horizontally-displaced rolling and snake rolling are higher than those assumed in plane strain compression with the same rolling reduction. The through-thickness distribution of the strain component εXX has a corresponding relationship with the plate curvature. In most cases, the plate will bent to the plate half with smaller average value of εXX, and the greater the difference between the average values of the upper and lower plate halves is, the greater the bending degree is. The width of the CSR has no clear correspondence with the bending direction and bending degree. The plate may keep straight even through the CSR exists, or bend when the CSR disappears.