Characterization On The Microstructure Of Severe Plastic Deformed Magnesium Alloy

In this paper, the deformation microstructures and mechanical properties of pure Mg and its alloys were analyzed and characterized by Electron Backscattered Diffraction(EBSD) and Transmission Electron Microscopy(TEM) and High-resolution Electron Microscopy(HRTEM), and Nanoindenter. The applied deformation forms include the Pin-Impact and Friction Stir(FSP) in the paper. The main results are showed as follows:(1) It was found high density twins and subgrain boundaries in Magnesium after Pin-Impact deformation. The strength of the materials were improved due to the large number twins, which can separate the grains effectively and refine them. The twins existence can improve the uniform plastic deformation of Mg and its alloys since it is one of the effective deformation mechanism of Mg and its alloys.(2) Friction Stir is the process where the force and temperature can increase.During this process, the thick second phases and the magnesium matrix were strongly stired together under stir-welding head. The matrix and the second phases were refined to some extent, the original net structure was broken and the crushing second phases diffuse in the matrix. The results of nano indentation showed that the Friction Stir can increase the hardness and strengthen of Mg and its alloys.(3) The second phase precipitation was broken under the friction stir process together as well as the original, and dispersed in the matrix, to have the dispersion strengthening effect.Thus Mg matrix grain refinement, The second phase supersaturated precipitation and the broken second phases diffuse in the matrix result the improvement of the Mg alloys.(4) In friction stir process, due to the effect of multiple external force, numbers of dislocations start to multiplication and slip, which lead to the grain refinement of second phases.