Research On Local Loading Forming Of Aluminum Alloy Squeeze Casting With Large Wall Thickness Dieeerence And Complex Shape

Squeeze casting technology combines the characteristics of liquid filling of casting and plastic deformation of forging.It is a kind of green and near net forming technology.The parts produced by it take a large proportion in the fields of automobile,communication,high-speed railway and electric power,especially in the automobile industry.Over the years,the quality of the forming parts has been greatly improved,but the forming technology of the parts with large wall thickness difference and complex shape is still insufficient,and the quality problems are easy to appear at the far end of the filling mold and the hot joint of the casting.In this paper,engine flywheel housing of typical aluminum alloy extrusion casting parts with large wall thickness difference and complex shape is taken as the research object,and the influences of forming process parameters,local loading forced feeding process parameters and heat treatment process parameters on microstructure and properties are deeply studied.It is expected to provide some references for the development and further application of squeeze casting technology for aluminum alloy parts with large wall thickness difference and complex shape.The flow field,temperature field and stress field in the filling and solidification process of flywheel shell were simulated by Procast numerical simulation software,and the locations of shrinkage cavity and porosity casting defects were predicted,which provided theoretical support for subsequent forming experiments.According to the designed orthogonal experimental scheme,the forming experiment was completed,the surface quality and internal macro morphology of the forming parts were observed,the mechanical properties of each position of the forming parts were tested,and the variance and range analysis were carried out on the experimental data.The results showed that,The optimal combination of process parameters is casting temperature 650 ?,extrusion specific pressure 48 MPa,mold temperature 220 ?,local supplementary pressure,supplementary calendering15 s The mold temperature has the most significant effect on the mechanical properties of the formed parts.Primary ?-Al grains are mainly equiaxed grains and cellular dendrites.The morphology of silicon in the eutectic phase is needle-like,and Si is easy to be segregated under pressure.In the position of local supplementary pressure,the tensile strength is greater than 180 MPa,the yield strength is greater than 100 MPa,and the hardness value is about 72.5 HV0.5.The local supplementary pressure can change the solidification state,produce plastic deformation and realize forced feeding.The pressure difference introduced by the supplementary pressure can realize feeding,which is also related to the volume of the supplementary pressure bar.The better the effect of feeding.According to the effect of pressure,the thickness of the area after pressure supplement can be divided into deformation area,direct action area and indirect influence area,and the corresponding microstructure morphology of different areas is different.With the increase of solution temperature and solution time,the mechanical properties gradually improve.The strength improvement of solution treatment is relatively limited,but it can significantly improve the elongation.After solution treatment,the optimal tensile strength is 243 MPa,the yield strength is 133 MPa,and the elongation reaches the maximum of 14%.The effect of aging at 175 ? and 180 ?for 4 hours on the strength improvement is basically the same,the strength value is first increased and then decreased with aging time,aging treatment for 8 hours the maximum strength value,the maximum tensile strength can reach 312 MPa,the maximum yield strength is 251 MPa.Si morphology change is more noticeable after heat treatment,can make different shape of Si spheroidizing and coarsening occurs,the small size of Si particles can be modified,the relative content of large Angle grain boundary to improve after heat treatment,have a recrystallization occurs,the fill pressure process with a certain degree of dynamic recrystallization,solid solution and aging treatment of recrystallization is not good.