Mechanical Properties And Microstructure Of Asymmetrically Rolled Pure Aluminium And Its Shear Deformation Observation

Asymmetric rolling (ASR) is one of the methods of severe plastic deformation (SPD), which can be used to produce materials with ultra-fine grains (UFG). In this thesis, rolling machine has been improved in order to achieve better rolled materials. Since the existence of insufficient friction between rollers and specimen, rolling process is always accompanied with sliding between them, thus the stability of rolling is greatly weakened. The roller of ASR machine is improved by making fine stripes on its surface, and the friction between roller and specimen is increased and the rolling machine improved. Results show that larger shear deformation has been achieved in the asymmetric rolling with mismatch ratio of 1.5.Shear deformation is believed to be a critical factor for grain refinement in UFG materials. Through inserting a small marked block into specimen shear deformation of ASR is directly observed. Further work has been done in order to understand the amount of shear deformation and its changes.Along with the observation of shear deformation, mechanical properties of specimen prepared by Conventional Rolling (CR), Asymmetric Rolling (ASR) and Improved Asymmetric Rolling (IASR) specimen have been thoroughly compared and contrasted by tensile test, observation of fracture surface and mircohardness test. It is believed that IASR is more likely to produce materials of better mechanical properties, such as higher strength and higher microhardness.In this thesis, the microstructure of rolled pure alminium has been studied by electron backscattering diffraction (EBSD) and transmission electron microscope (TEM). Severely deformed by IASR, the grains of Al are refined to about 500 nm, which exhibits greater ability of grain refinement of IASR than that of CR and ASR. Further studies have been done in order to clarify the effect of shear deformation on the mechanism of grain refinement.