Efficiently manufacturing large-scale isotropic Al7075 alloy sheets with submicron grain by multidirectional rotary forging

Abstract

Aluminum alloy sheets with higher isotropy and finer grains possess larger post-formability and better mechanical properties. However, it is extremely difficult to simultaneously realize the isotropy improvement and grain refinement by conventional plastic deformation process. In this paper, a multidirectional rotary forging (MRF) process was applied to tune the isotropy degree and grain structure of Al7075 sheets. The isotropy behaviors of microstructure and mechanical property along different testing directions were investigated, and the grain refinement behaviors were studied. The microstructure analysis indicates that initial anisotropic textures firstly transform to different single textures individually, and then the lattice orientations of all these different single textures strongly rotate along 〈110〉 crystal direction to form the same multiple textures along 〈110〉//normal fiber, i.e. isotropic τ-fiber. The mechanical property analysis indicates that isotropic yield strength and tensile strength were obtained by MRF deformation, which was mainly attributed to the combined effect of texture isotropy and dislocation density isotropy. Strong grain refinement was achieved under the deformation amount of 70 %, and the final grain size was ∼ 0.8 μm, which were mainly contributed to the interaction effects of strong lattice rotation, complex slip system activation and dislocation gliding.