The Experiment Research Of Ultralight Magnesium Alloy Of Submicro-scale Prepared By Severe Plastic Deformation

The microstructures of ingots and bars of conventional extrusion and equal channel angular extrusion(ECAE)of two types of Mg-8.2% Li(wt%) and Mg-8.2% Li-0.6% Zr alloys were investigated by means of optical and transmission electron microscopy and X-ray diffraction techniques. And ECAE process was simulated by 3-dimensional-elastic plastic method of finite element.Observations of optical microstructure indicated that two types of the alloys ingots had uniform distributions ofαphase andβphase.αphase of Mg-8.2%Li and Mg-8.2%Li-0.6%Zr alloys after conventional extrusion had uniform equiaxed grains and the grain sizes were respectively about 20μm and 10μm,andβphase was band structure which was parallel to the direction of extrusion.The specimen of Mg-8.2%Li alloy was extruded after the ECAE processing with route A and Bc by four passes at 300℃. Observation of optical microstructure indicated that dynamic recovery and recrystallization occurred during the ECAE processing. Grains were observably fined by ECAE processes with route A and Bc,and refine results from the first to third pass were more remarkable than the forth,and route Bc than A. After four passes with route A and Bc ,the mean grain sizes were respectively about 8μm and 4μm. Explorations of X-ray diffraction illustrated,during the ECAE processing,that the mechanical twin ofαphase didn,t occur and thatαphase of the alloys prepared by route Bc had uniform distributions of plane (1 011) and (1 010),but they didn,t by route A.The specimen of Mg-8.2%Li-0.6%Zr alloy was extruded after the ECAE processing with route Bc by four passes at 300℃. Observations of macrostructure showed that the banded structure ofβphase was"broken". Explorations of X-ray diffraction illustrated that during second pass the mechanical twin ofαphase occurred. The alloys after four passes rather had uniform distributions of plane (1 011) ofαphase and (1 10) ofβphase. Observation of TEM microstructure showed that slip bands and kink bands and regions of higher density dislocation exist inαphase and dynamic recovery and recrystallization ofβphase occurred after first pass. The twin boundary ofαphase run throughβphase that were not cut off during second pass also. Opposite sign of dislocations produced by the different dislocation sources canceled out each other and the same sign of edge dislocations...