| Pure magnesium and magnesium alloys had a lot of advantages,such as low density,high specific strength,and many other electronics,transportation and aerospace industry is the most development potential of the material,many products to plastic deformation pressure processing,most are casting magnesium alloy components on the market at present,it is hard to meet industrial engineering for its shape,size and mechanical property requirements.Magnesium and its alloys due to its own characteristics for early solidification structure and organization,appear easily in the process of plastic deformation defects such as cracks,the quality of products is often unstable.Based on magnesium and its alloy structure characteristics,this paper systematically studied the pure magnesium and its alloys in different solidification conditions,the evolution of organization after deformation conditions on the deformation characteristics and the influence of mechanical properties.The experimental results show that:As-cast magnesium is mainly composed of many shaft such as big grain,grain is very rough,about the average size is about 600 microns,part of the grain boundary mixed with a small amount of small grain,small grain size of about 200 microns,the microscopic metallographic organization has shown uneven fibrous structure.Under different stress conditions of pure magnesium solidification sample will to a certain extent affect CVCE deformation path and organization evolution,centrifugal solidification in the middle of the specimen due to small grain size,impurity is relatively small,plastic deformation ability is best,maximum deformation of 13 times.The solidified structure of magnesium alloy under the conditions of different centrifugal pressure characteristics is pure magnesium is more apparent.Significantly enhanced with the increase of the centrifugal stress,magnesium alloys,reduce the content of impurities,and beta phase morphology also have obvious changes,from thick strip into dispersion point,and decreased with the increase of pressure in the second phase content.AZ81 magnesium alloy with fibrous layered heterogeneous organization,grain size is uneven,part of the grain grew up serious stretched along the extrusion direction.In the process of extrusion,magnesium rod for grain oriented optimal distribution,most of the crystal plane parallel to the extrusion direction,pure magnesium and AZ81 magnesium alloy extrusion were strong base surface texture.In the process of deformation,the sample in the extrusion rod contact area crack,this for sample weak area,the biggest shear stress value was;Original sample the crack mainly in loose shrinkage cavity formation during deformation and fracture,sample after centrifugal pressurized solidification,loose shrinkage cavity within the organization is eliminated,the density increased,finally in the second phase of the discontinuous distribution of crack initiation,and on both sides of the crack microstructure is put in bigger difference.Continuous variable cross section extrusion deformation because of factors such as stress,there is uneven deformation,but along with the increase in deformation path,has been enhanced,the non-uniform deformation of extrusion for the first time is eliminated,eventually become a very tiny isometric,second phase and impurities on the grain boundary is a uniform distribution on the grain boundary.As-cast magnesium alloy mainly twin deformation process,the deformation occurred in the process of dynamic recrystallization.AZ81 magnesium alloy aluminum content is more,in the original sample on the grain boundary distribution inside a large amount of the second phase in the hard and brittle beta Mg17A112,easy to produce stress concentration in the process of extrusion deformation and crack initiation and fracture failure in the material,plastic deformation ability is relatively poor AZ31 and pure magnesium.But as-cast AZ81 magnesium alloy after six times CVCE deformation,grain refinement obviously,mechanics performance improved significantly. |
PDF Full Text Request