摘要
本文首先分别总结了微观孔洞和逆偏析2种凝固缺陷的形成机理及各自预测模型的发展,然后对二者的耦合预测模型发展做了概括总结,最后重点介绍了近期作者所建立的一个新的耦合预测模型。该模型首先利用气体元素在液-固-气三相中的分配规律,结合因液相在枝晶间补缩通道内流动受阻引起的局部压降,建立了一个新的微观孔洞预测模型;然后结合微观孔洞的析出对糊状区枝晶间补缩液流的影响规律,对经典的"局部溶质再分配方程"进行修正,得到一个新的逆偏析解析模型。针对以柱状枝晶方式定向凝固的Al-4.5%Cu(质量分数)合金的计算结果表明,凝固过程中微观孔洞的形成,会补偿糊状区中的凝固收缩,从而减少枝晶间的补缩液流,使糊状区枝晶间溶质富集程度减小,最终使逆偏析得到缓解。
Microporosity and inverse segregation are two common casting defects mainly caused by solidification shrinkage, which are detrimental to the mechanical properties of components, especially to the fatigue performance and ductility. Numerous efforts have been put into the investigation on microporosity and inverse segregation independently. However, few work has been done to establish a theoretical model for predicting the two defects simultaneously, whereas they often interact with each other and the formation of microporosity may exert a beneficial effect on inverse segregation. In this review, the coupling models for prediction of microporosity and inverse segregation were introduced. Firstly, the mechanisms and the predicting models for the two defects were summarized separately. Microporosity is a resultant of solidification shrinkage and gas segregation. Therefore, the porosity was previously categorized into two types： shrinkage porosity and gas porosity. More recent porosity models have combined the effect of pressure drop induced by feeding, the evolution of pores radius, the decrease of gases solu-bility in the liquid and the gas rejection at the solid/liquid interface, which provide rather good approximation to experimental results. As for inverse segregation, it is mainly caused by the suction of interdendritic liquid which is generally rich in solute. Therefore, determination of the feeding velocity is crucial for most inverse segregation models. Then, through the analysis of the underlying interaction between microporosity and interdendritic feeding flow, the coupling methods for prediction of the two defects were reviewed.Most of the models have added porosity into the continuity equation to amend the feeding velocity and utilized the＂local solute redistribution equation＂to get the solute concentration profiles. A new coupling model recently proposed by the present authors, based on analyses of the redistribution of gases element as well as the alloying element, is also in this route. The resul
作者
高志明
介万奇
刘永勤
罗海军
GAO Zhiming;JIE Wanqi;LIU Yongqin;LUO Haijun(State Key Laboratory of Solidification Processing, School of Materials Science and Engineering, Northwestern Polytechnical University, Xi＇an 710072, China;School of Materials Science and Chemical Engineering, Xi＇an Technological University, Xi＇an 710021, China)
出处
《金属学报》
SCIE
EI
CAS
CSCD
北大核心
2018年第5期717-726,共10页
Acta Metallurgica Sinica
基金
国家自然科学基金国际(地区)合作研究项目No.51420105005~~
关键词
微观孔洞
逆偏析
压降
气体析出
补缩液流
溶质再分配
microporosity
inverse segregation
pressure drop
gas precipitation
feeding flow
solute redistribution
