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金属学报  2018, Vol. 54 Issue (5): 717-726    DOI: 10.11900/0412.1961.2017.00501
  金属材料的凝固专刊 本期目录 | 过刊浏览 |
微观孔洞和逆偏析缺陷的形成机理与耦合预测研究进展
高志明1, 介万奇1(), 刘永勤2, 罗海军1
1 西北工业大学材料学院凝固技术国家重点实验室 西安 710072
2 西安工业大学材料与化工学院 西安 710021
Formation Mechanism and Coupling Prediction of Microporosity and Inverse Segregation: A Review
Zhiming GAO1, Wanqi JIE1(), Yongqin LIU2, Haijun LUO1
1 State Key Laboratory of Solidification Processing, School of Materials Science and Engineering, Northwestern Polytechnical University, Xi'an 710072, China
2 School of Materials Science and Chemical Engineering, Xi'an Technological University, Xi'an 710021, China
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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。

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    
Abstract

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 solubility 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 result shows that for Al-4.5%Cu (mass fraction) alloy solidified in a columnar dendrites structure, the predicted fraction of microporosity is a little smaller than that of Poirier's model, and the increase of initially dissolved hydrogen in the melt will decrease the solute enrichment in the interdendritic liquid. Microporosity seems to reduce the flow needed to compensate the solidification shrinkage, thus the solute segregation gets reduced. Finally, several suggestions were proposed, including the treatment of pore radius, eutectic shrinkage and gas porosity precipitated during eutectic reaction, etc.

Key wordsmicroporosity    inverse segregation    pressure drop    gas precipitation    feeding flow    solute redistribution
收稿日期: 2017-11-27     
ZTFLH:  TG21  
基金资助:资助项目 国家自然科学基金国际(地区)合作研究项目No.51420105005
作者简介:

作者简介 高志明,男,1989年生,博士生

引用本文:

高志明, 介万奇, 刘永勤, 罗海军. 微观孔洞和逆偏析缺陷的形成机理与耦合预测研究进展[J]. 金属学报, 2018, 54(5): 717-726.
Zhiming GAO, Wanqi JIE, Yongqin LIU, Haijun LUO. Formation Mechanism and Coupling Prediction of Microporosity and Inverse Segregation: A Review. Acta Metall Sin, 2018, 54(5): 717-726.

链接本文:

https://www.ams.org.cn/CN/10.11900/0412.1961.2017.00501      或      https://www.ams.org.cn/CN/Y2018/V54/I5/717

图1  A357合金凝固组织中的缩松与气孔
图2  Al-4.5%Cu合金凝固过程中枝晶间液相中的氢浓度变化及其溶解度变化
图3  微观孔洞形成的压力条件[11]
图4  孔洞发展的不同阶段
图5  定向凝固的Al-4.5%Cu合金柱状枝晶组织中,计算得到的糊状区各压力变化曲线(包括凝固收缩导致的压降、表面张力和气孔析出压力变化,以及合金的Scheil凝固路径)[11]
图6  利用Jie提出的微观孔洞模型[11]计算得到的不同初始H含量时的孔洞体积分数变化,以及用Poirier模型[9]计算的孔洞体积量变化
图7  垂直向上定向凝固示意图
图8  根据Mehrabian偏析模型[29]计算得到的Al-4.5%Cu合金溶质分布
图9  计算得到的不同初始H含量时,定向凝固的Al-4.5%Cu合金枝晶间补缩液流流速变化[11]
图10  定向凝固的Al-4.5%Cu合金在不同初始H含量时的枝晶间液相中溶质浓度分布[11]
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