Research On Semi-solid Squeeze Casting Of Copper Alloy Bushing And Its Heat Treatment Process

Semi-solid metal forming technology has the advantages of short flow,simple operation,low cost,and near-end forming.It has been widely used.ZCuSn10P1 copper alloy has good wear resistance,corrosion resistance,high mechanical properties,good process performance and other characteristics,is widely used in automotive,high-speed rail and ship equipment such as bearing bushings,valve switches,worm gear and other parts.At present,ZCuSn10P1 copper alloy bushings are usually prepared by casting methods.The preparation process is cumbersome and the formed products are prone to inclusion and oxidation problems.In this paper,semi-solid extrusion casting technology was used to prepare ZCuSn10P1 copper alloy bushings.Semi-solid ZCuSn10P1 copper alloy slurry was prepared by cold rolling-partial remelting technology.A set of four-piece extrusion casting bushing parts forming mold was independently designed.The semi-solid squeeze casting experiment was carried out to study the influence of forming pressure ratio,extrusion rate and other processing parameters on the microstructure evolution and mechanical properties of the ZCuSn10P1 copper alloy bushing;Then,the heat treatment experiment of the ZCuSn10P1 copper alloy bushing was conducted.The effect of processing parameters such as heat treatment temperature and heat treatment time on the microstructure evolution and mechanical properties of copper alloy bushings was investigated.The main research contents and research results of this paper are as follows:(1)A set of four-piece extrusion die-casting copper alloy bushing parts was designed and manufactured.According to the shape and size of the bushing parts,the punch die and the die were mainly designed and verified in detail,and the designed die was manufactured,assembled and tested.Experiments show that the use of a four-piece mold designed this time and the selection of reasonable forming process parameters can result in a smooth,clean,precise,and well-organized part product,while also improving the forming efficiency.(2)The effects of forming specific pressure and extrusion rate on the microstructure and mechanical properties of the bushing were studied.The results show that as the forming pressure increases,the homogeneity of the microstructure increases first and then decreases.The degree of plastic deformation near the position of the convex mold increases;At the same position,as the forming pressure increases,the liquid fraction decreases gradually.The grain size gradually decreases,and the shape factor decreases first and then increases.With the increase of the extrusion rate,the filling time is shortened,the filling ability is increased,and the organization uniformity is gradually increased.At the same position,as the extrusion rate increases,the liquid fraction,the average grain size,and the shape factor gradually decrease.As the forming specific pressure increases,the Brinell hardness and microhardness of the copper alloy bushing parts first increase and then decrease,the tensile strength increases first and then decreases,and the elongation gradually decreases.As the extrusion rate increases,the Brinell hardness and microhardness of the copper alloy bushing parts gradually increase,the tensile strength increases,and the elongation gradually decreases.When the forming specific pressure is 250 MPa and the extrusion rate is 15mm/s,the semi-solid squeeze casting process is the best.At this time,the liquid fraction is 22.3%,the average grain size is 77.96 ?m,the shape factor is 1.32,the hardness is 128 HBW,the microhardness values in the solid phase,liquid phase and solid-liquid two-phase area are 112 HV,193HV,and 156 HV respectively,the tensile strength is 387 MPa and the elongation is 2.8%.(3)The effects of heat treatment temperature and heat treatment time on the microstructure and mechanical properties of the bushing were studied.The results show that with the increase of heat treatment temperature,the morphology of semi-solid grains is improved,the microstructure uniformity is improved,and the grain size of solid phase increases with the increase of heat treatment temperature.With the increase of heat treatment time,the solid-liquid two-phase segregation phenomenon in the semi-solid tissue will be improved and the homogeneity of the microstructure will be improved.With the increase of heat treatment temperature and heat treatment time,the Brinell hardness of the semi-solid copper alloy bushing increases first and then decreases,the microhardness in the solid phase gradually increases,the microhardness in the liquid phase gradually decreases,and the microhardness in the solid-liquid two-phase area gradually increases,the tensile strength increases first and then decreases,and the elongation gradually increases.The heat treatment process at 350°C for 120 minutes is the best.At this time,the liquid fraction was increased by 3.4%,the average grain size was increased by 13.7%,the shape factor was reduced by 5.6%,and the Brinell hardness was increased by 6.25% compared with the same position of unheat-treated bushing parts.The microhardness in the solid phase increased by 20.5%,the microhardness in the liquid phase decreased by 4.1%,the microhardness in the solid-liquid two-phase area increased by 3.8%,the tensile strength increased by 3.9%,and the elongation increased by 60.7%.