Microstructure Andproperties Of Semi Solid Aluminum Alloy Prepared By Compound Stirring And Numercial Simluation

Turbulence filling and solidification shrinkage of aluminum alloy casting often lead to defects such as bubbles,porosity and shrinkage cavity,resulting in the decline of product performance,low yield and poor fatigue performance,seriously endangering the service life.The semi-solid slurry has rheological properties,which can improve the melt filling flow,reduce the solidification shrinkage,significantly reduce the shrinkage defects of castings,improve the mechanical properties and improve the life of parts.However,when the existing mechanical stirring is used to prepare semi-solid slurry,the ability of a single stirring shaft to drive the whole melt heat transfer is poor,the melt near the stirring shaft has sufficient heat transfer,the temperature is relatively low,and the whole melt has a large temperature difference,especially when the temperature control is unstable,the stirring shaft is easy to coagulate and hang.In view of the problem of traditional single shaft mixing,the basic principle of eccentric rotation is used for reference.Through the design of lower bottom plate,upper top plate,bearing seat and eccentric structure,the structure of ordinary rotation and eccentric mixing is combined,so that the mixing shaft can rotate eccentrically while rotating itself.The structure of semi-solid slurry mixing and motor lifting is designed and developed PLC is used to program,collect and control the rise and fall of the stepping motor and the temperature.At the same time,the visual control of the program is realized by combining the upper computer of the Internet of things and the touch screen;The effects of compound stirring and traditional uniaxial stirring on the temperature field,solid rate and shear rate of semi-solid slurry were analyzed by numerical simulation technology.The semi-solid slurry with uniaxial stirring and mixed stirring parameters was prepared by experiments,and the tensile specimens with mechanical properties were prepared by squeeze casting.Finally,the properties of the melt under compound stirring were analyzed The change of temperature field is related to the process of grain nucleation and growth.The results show that:Under the same conditions,the convection strength of the alloy melt can be improved by properly increasing the stirring speed of the stirring shaft,adopting the composite stirring process and increasing the revolution speed of the composite stirring;When the rotation speed of the stirring shaft is increased to 500 R / min,the average grain size is 145 ?m.The shape factor is 0.65 and the tensile strength is248.4mpa.The average grain size is 126 ?m.The shape factor is 0.78 and the tensile strength is 267.2 mpa;Compared with uniaxial stirring,the average grain size of composite stirring is 132 ?m at 300 R / min.The shape factor is 0.72,the tensile strength is 256.6 mpa,and the average grain size is 119 ?m at 500 r / min.The shape factor is 0.83 and the tensile strength is 276.2mpa;The average grain size is 120?m at300 R / min with the increase of the revolution speed of the stirring shaft?m.The shape factor is 0.81 and the tensile strength is 274.2 mpa;The average grain size is119 ?m at 500 R / min.The shape factor is 0.83 and the tensile strength is 276.2 mpa.Compared with the fluidity of the melt with uniaxial stirring,the composite stirring rotates in the stirring shaft and revolves in the melt at the same time,which further promotes the convection heat transfer of the melt,and the whole melt temperature and composition will be more fully mixed.Properly increasing the revolution speed can promote the heat exchange and reduce the melt temperature in a shorter time When the temperature range of semi-solid is lower,more supercooling and more nucleation can be obtained.The convection shear effect of composite stirring is also conducive to grain dissociation,increasing the number of nucleation and increasing the nucleation rate.At the same time,the temperature difference of melt decreases faster and smaller,the temperature field of melt is more uniform,which destroys the environment of dendrite growth,and tends to generate uniformly in all directions Long,the superposed grains rotate and collide with the melt flow,which is beneficial to obtain near spherical grains.