Research On Equal Channel Angular Rolling And Plastic Deformation Machnism Of AZ31 Magnesium Alloy Sheets

With desirable over-all properties, magnesium alloys are praised as the most prosperous green structural materials in the 21st century. Especially, wrought magnesium alloy sheets exhibit most extensive applicable opportunities, thus the research on which has been the focus all over the world. Aiming at the engineering problem of poor formability of magnesium alloy sheets at room temperature, this paper brings forward an academic idea for controlling basal plane orientation and develops a new processing technology, i.e., the equal channel angular rolling (ECAR) technology, and meanwhile makes a comparison between the sheet by 105°and that by 115°. Effects of these two different ECAR processing on the evolution of microstructure and mechanical properties in AZ31 magnesium alloy sheets were investigated. The main contents and results are as the following.Effects of ECAR on the evolution of metallurgical structure and basal plane orientation in AZ31 magnesium alloy sheets were investigated. The relationship among the processing parameters, microstructure and mechanical properties between the sheet by 105°and that by 115°was ascertained. Researches on the ECAR parameters of AZ31 magnesium alloy sheets by 105°and that by 115°were displayed. According to the study on the ECAR parameters, including the rolling pass, rolling route, preheating temperature and lubrication conditions, for 115°angle mould, substantive quantities of twin crystals appeared after 1 pass rolling, while the refining effect was not significant. Along with the increasing of rolling passes, twin crystals were significantly refined. After processed through the 4th rolling pass, twin crystals disappeared and the refining effects obviously exceeds that by 115°. The angle mould by 105°resulted in a greater degree of shear deformation and the initial basal plane orientation changed significantly. The effects of angle mould by 105°with 1 rolling pass on the basal plane orientation equaled that by 115°with 4 continued rolling passes.In comparison with ordinary rolling technologies, the plasticity of rolled sheets in the rolling orientation was obviously superior to that in the lateral direction. For sheets by 115°angle mould, the former elongation of 17.5% in the rolling orientation was promoted to 26.2%, while for sheets by 105°angle mould, the former elongation of 17.5% in the rolling orientation was promoted to 28.6%. According to the experiment with X-ray diffraction, the initial (0002) basal plane orientation of ordinary rolled sheets weakened significantly after simple tension, while that of sheet grain orientation showed a gradual increase. A careful observation of the microcosmic structure round the fracture proved that twin crystals existed in great quantities in ordinary rolled sheets, while decreased significantly in sheets by ECAR in the rolling direction. It was possibly because ECAR changed the grain orientation in magnesium alloy sheets, and the basal plane orientation turned into the non-basal plane orientation, thereby providing more slip systems for magnesium alloy sheets, while twining was just a auxiliary fracture mechanism. ECAR promoted the plasticity of AZ31 magnesium alloy sheets obviously. During the cup drawing test, there was a significant change in the fracture mechanism and an increase in anisotropy, and the plasticity of rolled sheets in the rolling orientation was obviously superior to that in the lateral direction, thus fractures in the rolling direction. The decrease of the angle and the increase of shear deformation greatly benefited the plastic deformation. The maximum erishen value of ECAR processed sheets using 115°angle mould was 6.1, and that using 105°angle mould was 7.0.