Microstructure And Compressure Deformation Of Semi-solid 7050 Aluminum Alloy Based On RAP Method

Semi-solid processing technology is a technology that utilizes the rheological properties unique to metal materials in the presence of solid-liquid coexistence.It is a new type of near-net forming technology with high efficiency,energy saving,near net shape production and high performance of formed parts advantage.With the deepening of the development and application of domestic automotive lightweight technology,the semi-solid forming technology of deformed aluminum alloy shape has received more and more attention.However,the deformation of semi-solid alloys has the sensitivity characteristics of its microstructure.The shear instability causes local defects such as cracks and holes,which seriously affect the internal quality of semi-solid alloy formed parts.Based on this,7050 aluminum alloy was used as the research object,and semi-solid alloy billet was prepared by recrystallization remelting(RAP).The microstructure and compressive deformation behavior of the alloy were systematically studied.The macroscopic behavior and microscopic deformation of semi-solid alloy were investigated mechanism.Through the research,the following research results were mainly obtained.1)The preparation parameters of 7050 aluminum alloy semi-solid billet are specified.The semi-solid temperature range of 7050 aluminum alloy is 483?~660?,which meets the requirements of semi-solid processing.An aluminum alloy having an extrusion ratio of 16 is more likely to obtain a crystal having a high degree of roundness during the remelting process.The increase of holding temperature and holding time can increase the recrystallization activation energy.When the limit is exceeded,the solid phase grain structure will be coarse and the average grain size will increase.The pre-denatured extrusion ratio of the determined semi-solid billet preparation was 16,the optimum holding time was 15 min,and the optimum heating temperature was 620°C.2)The generation of primary spherical grains is often accompanied by the production of liquid phase.The microstructure of the sample after extrusion deformation is mainly composed of strip-shaped and second-phase particles along the extrusion direction.After heating and remelting,the microstructure of the alloy sample evolves from a small strip-like structure to a larger isometric axis.Crystalline tissue.The liquid phase is first formed at the grain boundary or the sub-grain boundary.As the temperature increases and the holding time prolongs,the liquid phase in the crystal grows from small to large,and the number of liquid phases in the crystal first increases and then decreases.The inter-crystalline liquid phase begins to form and then grows to begin to coat the grains.3)The change of mechanical behavior during semi-solid compression is mainly related to the mechanism of solid phase force destruction,liquid phase drive and solid phase drive in the deformation stage of semi-solid alloy.As the billet temperature increases,the peak stress decreases significantly.The larger the strain rate,the higher the peak stress and the more severe the deformation and damage.When the solid phase ratio is high,the solid phase grain interaction causes local liquid phase expansion,and the effect of liquid phase driving deformation increases,causing local strain accumulation to produce local shear bands.During the deformation process,the liquid phase segregates to the edge of the sample,and the segregation is mainly related to the liquid phase fraction,the viscosity of the liquid,the average grain size of the solid phase particles,and the pressure gradient.The formation of the shear band is a process of solid-liquid separation.4)Radial constraints improve local deformation and liquid phase segregation.With the increase of strain,the stress increases,steadily and sharply rises under the radial constraint.The yield stress and yield strain of the specimen at 600? are greater than the yield at 620?.The yield stress and yield strain increase with increasing strain rate.In addition,under the radial constraint,the solid-liquid separation phenomenon in the internal deformation zone of the sample is reduced,and the local strain is effectively reduced.As the strain rate increases,the liquid phase distribution is more uniform.Under radial constraints,the internal pores of the sample are significantly less than600? at 620?.