Process Optimization Microstructure And Mechanical Properties Of Low Pressure Die Casting Of A356 Aluminum Alloy Wheel

Aluminum alloy is widely used in aerospace,weapons and equipment,automotive industry and other fields due to its low density,high specific strength and good mechanical properties,and has become the preferred material for lightweight design of automotive structures.Aluminum alloy wheel,as a typical vehicle part,is mainly produced by low pressure casting.Casting quality of wheel is closely related to process parameters.In order to study the effect of low-pressure casting process parameters on the filling and solidification process and forming quality of liquid aluminum,this paper takes low pressure casting aluminum alloy hub as the research object.Using the experimental method combining theory and simulation,the aim of optimizing process parameters and reducing casting defects was achieved,which provided the optimization direction and objective for the subsequent low-pressure casting production.MATLAB numerical programming and Pro CAST software are used to solve the boundary water cooling heat transfer coefficient.Based on the experimental data and Jmatpro software simulation,the thermal physical parameters is determined and assigned accurately.The results show that,the inverse optimal value of Pro CAST is 5004 W/m~2·K,and the heat transfer coefficient obtained by numerical program is 5148 W/m~2·K～4406W/m~2·K,through forward simulation verification,it is found that the accuracy of MATLAB numerical inverse solution is higher than that of Pro CAST software,but the requirements of numerical solution process and experimental data are higher than that of Pro CAST software inverse solution.The low-pressure casting process of A356 aluminum alloy hub was simulated by using Pro CAST finite element software.The effects of pouring temperature,holding time and different cooling processes on forming quality were studied.It is found that when the pouring temperature is 700℃and the pressure holding time is 80 s,the molten aluminum filling process is stable,the solidification process conforms to the principle of sequential solidification,and the probability of casting defects is the lowest.Under three different cooling and pressure holding processes of 300 L/h-150 s,400 L/h-140 s and 500 L/h-130 s,molten aluminum shows different solidification characteristics,and the wheels are in a sequential solidification state under the condition of 400 L/h-140 s.The optimized parameters are used to trial-produce the wheel,and its forming quality,structure and properties are analyzed.The microstructure and mechanical properties of different parts of the hub were analyzed.The results showed that the grain size of the hub gradually decreased from the inside to the outside,from 58μm of the center hub reduced to 23μm of outer rim.The tensile strength of the rim is 228 MPa,the yield strength is 170MPa,and the elongation after fracture is 6%.Comparing the tensile properties of the wheel rim under the process of 300 L/h-150 s and 400 L/h-140 s,it is found that the latter has higher tensile strength and elongation,178.9 MPa and 6.6%respectively.The reduction of casting defects in the wheel,the refinement of microstructure and the uniform distribution of eutectic Si particles are the main reasons for the improvement of its mechanical properties.