Details

Autor(en) / Beteiligte

• Gao, Zhiming
• Jie, Wanqi
• Liu, Yongqin
• Luo, Haijun

Titel

Solidification modelling for coupling prediction of porosity and segregation

Ist Teil von

• Acta materialia, 2017-04, Vol.127, p.277-286

Ort / Verlag

Elsevier Ltd

Erscheinungsjahr

2017

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• Porosity is a common casting defect induced by solidification shrinkage as well as gas segregation, nevertheless, it may exert a beneficial effect on reducing alloying element segregation. Unfortunately, the influence of porosity formation on alloying elements segregation in casting alloys have not been synthetically investigated by neither experiment nor theoretical analysis. In this regards, here a theoretical model, based on analyses of the redistribution behaviours of both gas element and the alloying elements, is proposed to simultaneously predict the porosity and segregation in as-solidified Al-based alloys. First, Al-4.5 wt pct Cu alloy with a columnar dendritic interface is selected to mathematically predict the porosity forming process. The modelling results show the same tendency with Poirier’s prediction, but the volume percentage of porosity calculated by the present model is lower than that of Poirier’s. Besides, the present model predicts a decrease in porosity fraction at late stage of solidification, and more than the previous studies, the gas escaped from eutectic liquid is also evaluated. Then, the impact of porosity formation on the velocity of interdendritic feeding flow is estimated, the porosity in the mushy zone apparently slow down the suction of interdendritic liquid. Finally, a mathematical model for element segregation is derived with consideration of porosity formation. Numerical results show that the solute enrichment in interdendritic liquid gets relieved slightly with porosity formation. Consequently, porosity will reduce the solute segregation. [Display omitted] For Al-4.5 wt% Cu alloy solidified with a columnar dendritic structure, the formation of pores in mushy zone can be predicted by combing the two effects of hydrogen segregation and the solidification shrinkage. The pressures inside and outside the gas bubbles is essential for the estimation of porosity. Besides, the formation of porosity necessarily affect the local redistribution behaviour of Cu element, consequently, Cu segregation is different from the case which no pore has been formed.