| Aluminum alloy is the most widely used material in lightweight applications.In recent years,the semi-solid forming process has opened a new way for the manufacture of aluminum alloy parts.The 319 s aluminum alloy is an Al-Si cast aluminum alloy,which is very suitable for semisolid industrial production.In actual production,reasonable casting gating system and process parameters play a key role in casting forming quality,but there is little research on semi-solid die casting forming of 319 s aluminum alloy at present.In this paper,the aluminum alloy truck bracket is taken as the research object,and the semi-solid die casting process is adopted and the solid model is established by using 3D modeling software.A gating system is designed,which includes a cylindrical sprue with gradually changing diameter,a sprue extension and a U-shaped trough runner.The Flow-3d cast casting simulation software was used to simulate the semi-solid filling process of castings.The influences of pouring temperature,mold temperature and injection speed on the filling quality of castings were studied by orthogonal simulation test system,the reasonable die-casting process parameters were determined,and the gating system of castings was optimized based on the simulation results.According to the optimized casting gating system and process parameters,the trial-production of die casting was completed,and the formability of the casting was evaluated.The microstructure and mechanical properties of castings were evaluated by optical microscope,scanning electron microscope,X-ray flaw detector,tensile tester and hardness tester.The effects of solution treatment and aging treatment parameters on the microstructure and mechanical properties of aluminum alloy die castings were studied by orthogonal test,and the best heat treatment parameters of aluminum alloy semi-solid die casting bracket were obtained.Orthogonal simulation experiment results of casting semi-solid die casting process parameters show that pouring temperature and injection speed have great influence on casting quality,while die temperature has relatively little influence.Within a certain range,with the increase of pouring temperature,the entrainment produced during mold filling of molten metal will decrease and the defects of oxidation inclusions will increase;With the increase of injection speed,the entrainment produced during mold filling of molten metal will increase and the defects of oxidation inclusions will decrease.The optimum semi-solid die casting process parameters of aluminum alloy bracket are pouring temperature 590?,injection speed 0.5m/s and mold temperature 260?.Combined with the simulation results,an overflow trough is added at the position where defects are easy to occur,and the thickness of the runner is optimized to be 10mm,thus obtaining the casting gating system with the least defects of entrainment and oxidation inclusions.The trial production results show that under the optimized casting gating system and process parameters,the casting is well formed and no surface defects are found.Increasing the pressurization pressure will enhance the feeding ability of castings during solidification.When the pressurization pressure is 100 MPa,a semisolid spherical structure with uniform grain distribution and high degree of roundness can be obtained.The average grain size D of ?-Al is63.2?m and the shape factor F is 0.8.The internal quality of castings is obviously improved,and there are no defects of cracks,shrinkage cavity and porosity.The orthogonal test results of heat treatment show that the best heat treatment parameters of aluminum alloy bracket castings are solution temperature 470? and time 4h;The aging temperature is 170? and the time is 12 h.Under these technological parameters,the mechanical properties of castings can reach 375 MPa tensile strength,320 MPa yield strength,4.3% elongation and 121 HBW hardness. |
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