Microstructure And Properties Of Semi-solid Rheological Squeeze Casting CuSn10P1 Alloy Thin-walled Bushing Fabricated

Thin-walled bushings are usually used in environments with high temperatures,high alternating loads and high-speed heavy loads.Such harsh working conditions lead to a limited life.CuSn10P1 alloy has the advantages of high strength,large elastic modulus,low friction coefficient,high wear resistance and corrosion resistance,Therefore,it is widely used in aerospace,transportation and other fields.However,the parts prepared by the traditional liquid squeeze casting process have defects such as coarse grain structure,shrinkage cavity and internal micropores,resulting in poor comprehensive performance of the parts.Semi-solid forming technology can effectively refine grains,improve shrinkage cavity and other defects,and obtain castings with dense structure and excellent performance.This article takes CuSn10P1 alloy thin-walled bush(3.5 mm)as the research object,On the basis of preparing the semi-solid slurry by the melt-confined flowinducing nucleation device in the early stage,The bottom injection type extruder is used for one-cavity six-die semi-solid rheological squeeze forming,The forming parameters(forming specific pressure,squeeze speed,mold temperature)and the influence of the runner on the structure and performance of the bushing were studied to obtain the best squeeze process for semi-solid flow-forming thin-walled bushings.The comparison of the microstructures of liquid squeeze casting and semi-solid rheological squeeze casting found that there are coarse dendrites in the microstructure of the liquid squeeze casting CuSn10P1 alloy bushing,and the microstructure of the bushing is poorly uniform.However,the liner prepared by semi-solid rheological squeeze casting made by melt-constrained flow-inducing nucleation process has fine microstructure and uniform distribution,mainly equiaxed crystals or nearly spherical crystals.During rheological squeeze casting,forming a specific pressure of 110 MPa will lead to many defects such as poor microstructure density and shrinkage shrinkage of the bushing;when forming a specific pressure of 190 MPa,the liquid phase will preferentially flow in the direction of smaller specific pressure liquid-phase aggregation occurs,leading to obvious solid-liquid separation;when the forming pressure is 130 MPa or 150 MPa,a good solid-liquid synergistic filling effect can be obtained,and the liner microstructure uniformity and grain refinement degree are better.When the filling rate of rheological squeeze casting is 14 mm/s,the complete parts cannot be obtained;when the filling speed is 22 mm/s,it is easy to make the gas in the cavity too late to overflow and cause the phenomenon of air entrainment,and the defects such as shrinkage cavity and even pores;When the filling rate is 18 mm/s,the microstructure distribution is uniform and fine.When there is no cross-runner,the temperature of the mold rises,the microstructure distribution of the flow-shaped bush is more uniform,and the defects such as shrinkage are reduced;when there is a crossrunner,the mold temperature has little effect on the distribution and size of the microstructure.When thin-walled bushes are formed by rheological squeeze,with or without a runner,the tensile strength,elongation,and brinell hardness all increase first and then decrease with the increase of forming specific pressure and filling rate.The influence of the mold temperature on the hardness tends to increase first and then decrease with the increase of the mold temperature,but the influence law of tensile strength and elongation is different.When there is a runner,the tensile strength and elongation tend to increase first and then decrease as the mold temperature increases.When there is no cross-runner,the trend is increasing continuously.When there is a cross-runner,the optimal forming process parameters of the rheological thin-walled bushing are the forming specific pressure of 150 MPa,the filling rate of 18 mm/s and the mold temperature of 475?.Its tensile strength,elongation and hardness are 451.0 MPa,32.6% and 140 HBW,which are 26.3%,317.9% and 18.6% higher than liquid squeeze casting,respectively.The best process parameters of the thin-walled bushing without flow runner are the forming pressure 130 MPa,the filling rate 18 mm/s and the mold temperature 500?,its tensile strength,elongation,brinell hardness are 480 MPa,29.0%,and 132 HBW,which are 26.3%,310.2%,and 7.3% higher than liquid squeeze casting,respectively.