Research Of ECAP And Controlling Of Material Microstructure And Property

Moderate refinement of grain is an effective method to enhance service and shaping properties. ECAP(Equal-Channel Angular Pressing) is one of the most promising industrial techniques that can refine conventional grain size to submicrometer or nanometer level. Recently, it has become the hotspot of research. Systemic research was investigated about ECAP in this paper, including design and fabrication of the experimental device, caculation formula of the strain, ECAP of Cu and Cu matrix composite, ECAP of LY12 alloys , microhardness and microstructural stability of the produced ultra-fine grain and so on.By pressing with four different routes for three passes, the experiments confirm that the development of microstructure of grains separated by high angle boundaries occurs more rapidly in route Be, and the amplitude of microhardness is the most rapid.The results of pure Cu show ECAP can produce bulk material of submicrometer level indeed. As the number of passes increases, the initial structure of pure Cu has been refined largely. After six passes, i.e. the equivalent true strain of 4~5,the grain size gradually becomes stable and uniform. After ten passes, the average grain size of the microstructure which including high angle boundaries is about lum. The Vickers hardness increases rapidly after ECAP, from 78.7HV to 185.3HV. And as the number of ECAP passes increases, the rate at which softening occurs in the transition zone increases and the onset temperature of recrystallization drops. Moreover, the grain size after static recrystallization is more finer, so grain size can be further refined by controlling the temperature and time of recrystallization. Recrystallization begins after annealing at 433K for 60 min, and then the Vcikers hardness decreases.The ECAP results of different initial grain show initial grain have a great influence on the refinement of grain. More equiaxial and uniform the initial grain is, it is more favorable for the refinement of grain.The experimental results of 1 .0vol%SiCp/Cu after ECAP at room temperature show that ECAP has a little influence on the distribution and refinement of the reinforced particle. Cracks can be found after three passes at room temperature. The Vickers hardness of the composite increases from 92.4 HV to 177.0 HV.ECAP was successfully used to refine LY12 alloy to 0.5 m at room temperature after seven passes. The pretreatment process concluded from experiments was solution treated at 500 for 2h and overaging at 400 for 8h.The refinement mechanism of grain at room temperature can be described as dislocation tangle and dislocation node form in the initial grain with severe plastic deformation, then the dislocation node form subgrains or grains. Subgrains become grains by snipping of the subgrain boundaries under the action of shearing stress.