Deformation And Bending Optimization Of Asymmetrical Rolled 7xxx Series Al Alloy Plate

Asymmetric rolling (ASR) can reduce the casting defects and improve the homogeneity of microstructure and mechanical properties significantly due to the introduction of severer additional shear deformation, which has been widely used in fabrication of strip and foil products. However, the serious bending behavior limits the promotion of ASR process in production of plate. Therefore, the key issue is how to simultaneously introduce server plastic deformation while to achieve a minimum bending curvature in production of plate. In this dissertation, the deformation behavior and microstructural evolution of 7000 series Al alloy plate during ASR were systematically investigated using the finite element (FE) and experimental methods, and the correlation of the rolling parameters and the bending curvature of ASR processed plate was studied systematically. The non-bending ASR process controlled by several key rolling parameters was presented. Finally, the multi-pass non-bending ASR processes were applied to the pilot plant rolling, the ASR-processed plate with flat profile was obtained and significant improvements in mechanical properties were also achieved as compared to the SR-processed one. The conclusions are summarized as follows:The total shear strain in the ASR rolling deformation zone consists of two parts:the positive shear strain introduced in the forward slip zone and the negative shear strain introduced in the backward slip zone. According to the result, the total shear strain in multi-pass ASR was calculated and found that it enhance significantly, especially in the middle thickness of rolled plate, which improved from 0.026 obtained by SR to 0.836 introduced by ASR.The deformation of ASR processed 7050 Al alloy plate was directly observed through the engraved marks on the lateral surface of plate. It shows that the severe shear deformation was introduced throughout the thickness of ASR processed plate compared with the SR, in which the shear deformation concentrates on the surface only. Althrough the shear strain on the surface in ASR is still higher than that in the middle thickness, which results in the heterogeneity of deformational distribution. However, the shear and compress strain at the middle thickness of plate introduced by ASR are in the same magnitude, which enhance the homogeneity of microstructure.With a constant total rolling reduction, much more shear deformation can be accumulated with the decreasing thickness reduction per pass (TRPP), which improves the homogeneous distribution throughout the thickness of rolled plate. The recrystallized grain size decreases and distributional homogeneity throughout thickness increases with decreasing TRPP. The ASR-processed plate at the TRPP of 10-30% exhibits the best elongation and homogeneity in T6 condition; the deformation route of ASR-R can enhance the homogeneity of deformation and microstructural distribution throughout the thickness of ASR processed plate due to the interaction of additional shear deformation between the adjacent passes.The correlation of the rolling parameters and bending curvature of ASR processed plate was systematically investigated. The correlation diagram and empirical equations between the rolling parameters including of the differential speed ratio, roll diameter and initial thickness of plate and the critical thickness reduction per pass are presented; the pilot-plant multi-pass non-bending ASR process was studied and the multi-pass ASR processed plate with flat profile was obtained in a 40mm 7050 Al alloy plate. The mechanical property and fracture toughness in LT and TL directions of ASR-processed plates in T6 state are improved significantly.