The Solidification Simulation Of Al-Si Alloy

Al-Si alloys are of great potential in industry, architecture, transportation, chemical industry and national defence for their appreciated properties, such as excellent casting capability, and the component is steady, homogeneous and easy to melt and batch feeder.The shrinkage cavity and porosity are the main defect for producing Al-Si alloys castings. In the present paper,the prediction of the cavity and porosity during solidification have been studied systematically on Al-Si alloys. This paper is component of three modules: the mathematic model of temperature field, the mathematic model of cavity prediction and the mathematic model of porosity prediction.Combined with Al-Si phase graph, based on the fundamentals of solidification and principle of heat transfer, the mathematic model of temperature field has been built. By the phase graph of Al-Si alloys, I have taken into my account that the primary crystal transformation and the eutectic transformation during the solidification. So, pointed to the treatment of solidification latent heat, both temperature compensation method and equivalent specific heat method have been used. During the solidification range, the equivalent specific heat has been used; during the eutectic transformation range, the temperature compensation method has been used. By the work mentioned above, the accurate mathematic model of temperature field has been built, so to do the solid base for the later prediction of cavity and prediction of porosity.About the problem of cavity prediction during the solidification of Al-Si alloys, the molten pool of cavity has been correctly determined by the combination of the dynamic determination method of liquid isolated multiple molten pool and the criterion of solid liquid interface. During the prediction of cavity, the critical solid fraction combined with the synthetic method of shrinkage mass is used to be the criterion to predict cavity. In order to predict the volume of cavity accurately, during the calculation of shrinkage volume, only the liquid shrinkage and the solidification shrinkage have been taken into our account, and the solid shrinkage has been ignored.About the problem of porosity prediction during the solidification of Al-Si alloys, the molten pool of porosity has been correctly determined by the dynamic determination method of liquid isolated multiple molten pool. The pressure of the liquid metal which influences the formation of porosity is introduced into this prediction method. Taking the presence of eutectic platform into account, the temperature gradient is replaced by the solid fraction gradient. And, the concept of cooling velocity is amended, the concept of equivalent cooling velocity is introduced firstly. Based on these improvements, the new criterion about theprediction of porosity ,namely P₀·G_s/R_e^1/2 ≤ K, is deduced, P₀ —the pressure of the liquid metal cell,G_s— the solid fraction gradient, R_e—the equivalent coolingvelocity. So, the formation of porosity can be accurately predicted during the solidification of Al-Si alloys.Finally, taking the alloy of ZL102 and the mould of ht150 as the example, ignoring the covering material of surface, a casting test about a group of steps was did. By the comparison between the simulation results and experimental results, it is showed that the simulation results coincided with the experimental results quit well. By carrying out the experimental verification, we can see that this software is accurate about the prediction of cavity and porosity during the solidification of Al-Si alloys.