Numerical Simulation And Crafts Research Of Low Pressure Casting Process Of Aluminum Alloy Casing

With the increasing requirements of aerospace lightweight,aluminum alloys are widely used in the manufacture of castings,and higher requirements are placed on the mechanical properties and metallurgical quality of castings.Low-pressure casting technology has unique advantages in aluminum alloy molding,and has received more and more attention in recent years.However,our country's research on low-pressure casting started late,especially the application in the aerospace field is largely affected by the original gravity casting process design,and lack of theoretical basis in the design of low-pressure casting process for complex structural castings.Regarding the problems above,this paper systematically studies the effects of low-pressure casting process and subsequent heat treatment of typical aluminum alloy casing castings on casting defects and residual stress.A simple geometric structure is designed,and the influence of the cavity structure parameters on the free surface flow state of the molten metal during the low-pressure casting process is studied by FLOW-3D numerical simulation,and the critical filling speed of the low-pressure casting of ZL114 A is determined.According to the structural characteristics of the casing casting,five casting system schemes were designed,and the low-pressure casting process of the five schemes was simulated by PROCAST,which clarified the ideas of controlling the casing casting defects and revealed the influence and mechanisms of the filling pressure parameters on the casting defects.Finally,the residual stress of the casting during solidification and heat treatment was analyzed,and the stress state of the casting during solidification and heat treatment was expounded.The main results are as follows:The critical filling speed of ZL114 A alloy melt low-pressure casting at 720?is between 0.2m/s and 0.3m/s,which is less than the theoretical value of the critical filling speed of aluminum alloy(0.5m/s).Under the restriction of the mold wall,the oxide film is involved in two forms: liquid surface oscillation and continuous involvement.When the filling speed is not high,the later stage may change from oscillating filling mode to stable filling mode.When the filling speed is high,the later stage changes to a stable continuous oxide film involved.The cavity cross-sectional area ratio and the cross-sectional aspect ratio have no effect on the critical filling speed,but the change of the cross-sectional aspect ratio will affect the oxide film entanglement process of later filling.The greater thecross-sectional aspect ratio deviates from 1,the more difficult it is to form a continuous oxide film involved.Compared with the lateral and vertical casting positions,the horizontal casting position of the casing is more conducive to the control of the filling flow field and solidification temperature field.In order to reduce the solidification defects,the top of the casting should be provided with a heat riser,and the filling pressure rate should be appropriately increased to shorten the filling time without causing turbulence in the filling,the heat loss of the molten metal during the filling process is reduced,and the riser temperature is increased.The maximum residual stress after casting solidification is 120 MPa,the thickness of the side wall is relatively thin,the stress distribution is relatively uniform,and the equivalent stress in most areas is 80?90MPa.Before the heat treatment,the casting riser and part of the casting system are removed,and the solidification stress can be basically released.In the subsequent heat treatment process,the residual stress of the casting showed a trend of increasing first and then decreasing.The maximum equivalent residual stress of the casting residual stress after solution treatment is 23 MPa,and the maximum deformation displacement is close to 6mm.During the quenching process,the temperature difference between each part of the casting is large,and the cooling speed is fast,and the maximum residual stress of the casting reaches 80 MPa.After artificial aging,the residual stress and deformation of the casting were significantly reduced,the maximum stress was reduced to below 20 MPa,and the maximum deformation of the casting was also reduced to below 0.9mm.