| With the further development of semi-solid processing theory and practice,the industrial application is becoming more and more mature.Rheo-squeeze technology has become the focus of research because of its short process,low energy consumption and other advantages.Squeeze casting is a typical process for non shrinkage casting because of its high pressure solidification and plastic deformation.In this paper,the basic research of rheo-squeeze casting technology is carried out by combining the semi-solid pulping and squeeze casting technology closely and combining the excellent characteristics.A semi-solid vertical squeeze casting equipment with translational casting and injection system has been developed.A set of special squeeze casting mold has been designed and developed.The influence of its technological parameters on the forming of casting aluminum alloy and Forging Aluminum Alloy by rheo indirect squeeze casting has been systematically studied.Anycasting simulation software was used to simulate the solidification process of the round workpiece of the alloy 7075,and the experimental research of rheo direct squeeze casting of the alloy A356 was carried out.The main contents and conclusions are as follows:Squeeze casting on injection mechanism,forming equipment locking mechanism and its control system,design and development of the special supporting squeeze casting mould design and manufacture;semi solid vertical gating system with translational squeeze moulding machine,to achieve the translational pressure casting solidification way of squeeze casting;upgrade Low Superheat Pouring with a Shear Field(LSPSF)process control system based on PLC,the process parameters can achieve precise control;the development of special squeeze casting mould,the insert type structure,by connecting the innovative design of punch structure and type of the oil cylinder,can squeeze two times in the squeeze casting cavity forming(forging)function.The microstructure of A356 alloy parts formed by rheological squeeze casting by analysis of LSPSF pulping process shows that the microstructure of solidification crystallization under pressure is evenly distributed,and the primary alpha-Al phase is fine and non dendritic,and the appearance precision of A356 rheological squeeze casting is better,the apparent light finish is high,the performance is stable,and the average tensile strength is more stable.The strength is 190.5MPa,the average elongation is 13.13%,the maximum elongation is over 19%,and the rheological extrusion casting is easy to form a complex A356 piece.Through the setting of the exhaust and overflow slot,the cold septum and inclusion are easily controlled,and the quality and performance of the parts tend to be stable.The two step thermodynamic calculation hypothesis of rheological forming is carried out.The first stage of solidification occurs in the slurry accumulator and cylinder,which is considered as a equilibrium state.The second stage occurs under the condition of high pressure cooling in the mold cavity,which is considered as a non-equilibrium solidification.The Scheil model can be used for thermodynamic calculation.By using Anycasting software,the numerical model of high quality 7075 alloy wheel shaped squeeze casting is obtained by orthogonal experiment.Compared with that of the simulation model,the defects and the numerical results indicated that when the pouring temperature is 635?,the filling speed is 0.2m/s,the mold temperature is 200?,the probability distribution of minimum defect parameters,can obtain excellent quality of squeeze casting parts,consistent with the actual process parameters.Through the LSPSF pulping process and special squeeze casting joint forming equipment,continuous production test realized alloy 7075 wheel shaped parts results show that when the pouring temperature is 630~636?,the mold temperature is 200?,the holding time of 15 s and 80 MPa injection pressure,squeeze casting forming 7075 Alloy wheel parts of good appearance quality,microstructure,fine grain roundness,no dendrite;average tensile strength is 299 MPa,the average elongation is 15.32%,the maximum elongation rate reached more than 23% with mechanical properties;squeeze injection pressure increases the tensile strength increased,but the ductility increased no longer in a certain increase,experiment under the condition of pressure 80 MPa can obtain excellent parts;explores the different effects of pressure on the grain size and liquid phase segregation,with the increase of squeeze pressure,grain size becomes small,the more obvious the liquid-phase segregation is.To explore the mechanism of heat treatment of rheo-squeeze casting 7075 parts to strengthen,under the experimental conditions of 7075 alloy rheo-squeeze system of single aging heat treatment process casting parts T6: 475? solid solution treatment,insulation 2h,room temperature water quenching,the aging temperature is 140?,16 h insulation,air cooling.After heat treatment,7075 alloy rheological mechanical properties of cast alloy squeeze parts increased significantly,the average tensile strength is 520 MPa,the average yield strength is 467 MPa,the average elongation is 9.05%,the maximum tensile strength reaches 552 MPa,the maximum yield strength reaches 500 MPa,the maximum elongation is 13.77%,the best performance indicators have reached the level of forging.The microstructure of 7075 alloy in rheo-squeeze casting was studied.After the solution treatment,there were various pores left by the low melting point eutectic phase near the grain boundary.After T6 treatment,the tensile fracture surface also found a variety of initial melt holes along the grain boundary.These holes would seriously affect the mechanic properties of the parts.The tensile fracture of heat treatment is composed of the large dimple,flat area,compact shallow dimple and tearing ridge.From the microscopic characteristics of the tensile fracture,the tensile fracture mechanism of the hole and hole is found to form the tear zone.The hole in the tensile fracture is deposited in the form of the large dimple,and the tear crack germinating from the pore.Then,with the increase of tensile stress,pores and holes gather and expand,forming ripped rip until finally breaking.After the 7075 alloy rheo-squeeze casting,the spherulites are more and the grain is fine and uniform.When the solid solution treatment,the smaller the grain spacing and the greater the stress,there are a large number of dislocation and vacancy in the matrix,which can effectively accelerate the diffusion and dissolution rate of the alloy elements,especially the copper elements,and the solution time has been significantly shortened and the production has been promoted. |
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