Filling Behavior,Microstructure And Mechanical Properties Of Thin-walled AlSi10MnMg Castings During Die Casting Process

Thin-walled casting of aluminum alloy with characteristic of light-weighting and good mechanical properties has good prospect in producing large complex structure such as vehicle body and automotive chassis.High pressure die casting(HPDC)as a quick near-net shape forming is suitable for integration design and integral forming of these castings.However,there are several problems in thin-walled complex structure die casting such as low filling capacity instable microstructure and mechanical property.Therefore,the study of flow behavior in filling processing,microstructure and mechanical property of thin-walled die casitng of aluminum alloy can provide theoretical guidance for HPDC processing design and optimization.Simulation model for thin-walled die-casting of aluminum alloy was built and coupled with experimental result to study flow behavior,microstructure and mechanical property of AlSi10MnMg alloy.The viscosity of AlSi10MnMg alloy was measured using rotation cylinder viscometer and its characteristic was also discussed.Interface heat transfer coefficient(IHTC)between the casting and mold was obtained by experiment.Viscosity and IHTC between the casting and mold were used for simulation.Simulation model is evidened by comparing simulation and experimental observation.Fluid dynamics parameters during die casting were calculated on basis of experiment.Flow characteristics during the filling processing were discussed by considering fluid dynamics parameters and simulation.The model of metal liquid filling for thin-walled die-casting of aluminum alloy was also developed.Microstructure and mechanical property at the entrance of fluidity specimen and along the fluidity length were studied by simulation and experiment.The model of porosity distribution along the fluidity length for thin-walled die-casting of aluminum alloy was established.The simulation model was successful appied to optimize the technology of thin-walled aluminum alloy motor cover.Following results were obtained:The rotation cylinder viscometer is suitable to measure viscosity of aluminum alloy melt with characteristic of non-Newton fluid.AlSi10MnMg aluminum alloy melt displays a series of changes with temperature decreasing,contributing that viscosity evolution with temperature decreasing can be divided into four stages.Because of fast filling velocity and short filling time of thin-walled casting of aluminum alloy during die casting,there are two different stages during filling process:one is liquid filling stage;another is liquid/solid filling stage.IHTC between the casting and mold of these two stages were obtained and discussed,respectively.At pouring temperature range of 923 to 1013K,the critical filling length of thin-walled die-casting of aluminum alloy is in the range of 510 to 810mm.The following fluid dynamics parameters during filling processing were obtained from experiment:Re<2000 and We>60.It can be concluded by coupling fluid dynamic parameters and turbulence simulation that aluminum alloy melt fills the cavity of thin-wall fluidity specimen at a high-speed in the form of laminar flow with the melt free surface breaking into small droplets.On basis of above conclusion,the model of metal liquid filling for thin-walled die-casting of aluminum alloy was built.The aluminum alloy melt is always in the form of the spray and the "Full thickness"during filling processing.Coupling simulations with experimental observations,porosity of fluidity specimen of thin-walled casitng of aluminum alloy along the fluidity length decreases firstly and then increases,suggesting that the model of porosity distribution along the fluidity length can be divided into four parts.Density along the fluidity length is affected by fluidity.Primary a-Al phase is refinement and uniform with pouring temperature increasing,while the distinction of primary a-A1 phase along the fluidity length can be neglected.Mechanical properties at the entrance of fluidity specimen firstly increase and then decrease with pouring temperature increasing.At low pouring temperature,mechanical properties dramatically decrease and are mainly affected by porosity.At high pouring temperature,the difference of mechanical properties along the fluidity is insignificant and obviously influenced by pressure.