Effect of asymmetrical and symmetrical rolling on mechanical properties of 7075 aluminum plates

To further develop a highly efficient rolling process for 7075 aluminum plates, this paper carried out an experimental study on the effects of asymmetrical and symmetrical rolling on the mechanical properties of 7075 aluminum plates, and adopted four different rolling cumulative deformation ratios. The experiment was conducted in two steps. The first step was an experiment on the variation of the bending degree of the rolled plate with different asymmetrical rolling speed ratios. The distances y between the highest point of the inner bent surface and the horizontal bottom surface, and the distance x between the inner surface's two contact points of the bent inner surface and the horizontal bottom surface were measured, with the inner surface of the rolled plate facing the horizontal bottom surface. The y/x value was used to describe the bending degree of the rolled plate. The second step was asymmetrical and symmetrical rolling experiments. The experimental results show that the bending degree of the rolled plate is the maximum when the speed ratio is 1.12, and the y/x value can reach 0.222 18. However, even though the same design cumulative deformation rate is used, the actual cumulative deformation ratios of the rolled plates produced by asymmetrical and symmetrical rolling differ by 1% to 2%. When the actual cumulative deformation rate of the rolled plate reaches 76%, the recrystallization in the rolled plates is more effective during T6 heat treatment, and the amount of small and medium-sized crystal grains generated by recrystallization increases. After T6 heat treatment, a large number of dimples with a size of less than 1 μm and small second phase particles with a size of less than 100 nm can be visible in the fracture of the 7075 aluminum plates after 6 passes of asymmetrical and symmetric rolling. Asymmetrically rolled 7075 aluminum plate has smaller dimples than that in symmetrically rolled. Compared with symmetrical rolling, asymmetrical rolling just slightly increases the strength of the 7075 aluminum plate. When a specific level of deformation is reached, the strength peak of the 7075 aluminum plate rolled symmetrically will appear. However, the strength of the 7075 aluminum plate by asymmetrically rolling continually increases with increasing rolling cumulative deformation ratio.