【作者】 郝良品；

【导师】 田学雷；

【作者基本信息】 山东大学 ， 材料加工工程， 2007， 硕士

【摘要】 Al-Si合金具有优良的铸造性能，具有成分较稳定、均匀、易于熔配等优点，在工业生产、建筑、交通运输、化工、国防建设等方面有广阔的应用前景。本文以Al-Si合金为研究对象，因为缩孔缩松成为其产生废品的主要原因，所以本文主要针对Al-Si合金凝固过程中的缩孔、缩松预测进行研究。主要分为三个模块：建立温度场数学模型；建立预测缩孔的数学模型；建立预测缩松的数学模型。本文以凝固理论、传热学原理等为基础，结合Al-Si合金的相图，建立了温度场的数学模型。根据相图，考虑到Al-Si合金凝固时发生初晶转变和共晶转变。因此，在对结晶潜热的处理上，同时采用了等价比热法和温度回升法。在初晶凝固区间采用等价比热法；在共晶凝固区间采用温度回升法。并根据成分利用杠杆定律来计算初生相和共晶相的潜热，建立了较为准确的温度场模型，为以后的缩孔缩松预测做好了充分的准备。在对凝固过程的缩孔预测方面，将多熔池判别技术与Al-Si合金的固液界面判据相结合，对缩孔熔池进行了准确的划分：在预测缩孔的过程中，以临界固相率与收缩量综合法为标准；为了精确预测缩孔的体积，考虑到固态收缩对缩孔的形成影响不大，因此本文在计算体积收缩量的过程中，只考虑液态收缩和凝固收缩，而对固态收缩则忽略。在对凝固过程的缩松预测方面，利用多熔池判别技术对缩松熔池进行了准确的划分；将影响缩松形成的压力项引入Al-Si金缩松预测的判据中；考虑到共晶平台的存在，用固相率梯度代替了温度梯度；提出了等价冷却速的概念，对冷却速度进行了修正。更准确地反映了凝固的真实过程；基于这些改进，建立了预测缩松的新判据，即P₀·G_s／（R_e）^1/2≤K，其中，P₀代表凝固单元受到的压力，G_s代表固相率梯度，R_e代表等价冷却速度。对Al-Si合金凝固过程中缩松的形成进行了精确预测。最后，以合金ZL102、铸型ht150为例，不考虑表面涂料的情况下，进行了一组梯形件的浇铸实验。通过将模拟结果与实际浇注结果进行对比，结果表明：对缩孔缩松缺陷的预测情况与该产品实际生产结果基本吻合。验证了本软件对Al-Si合金凝固过程中缩孔缩松预测的准确性。更多还原

【Abstract】 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.更多还原