TY - JOUR

T1 - Macrosegregation Formation in an Al–Si Casting Sample with Cross-sectional Change During Directional Solidification

AU - Zhang, Haijie

AU - Wu, Menghuai

AU - Zheng, Yongjian

AU - Ludwig, Andreas

AU - Kharicha, Abdellah

PY - 2018/10/6

Y1 - 2018/10/6

N2 - A unidirectional solidification experiment of hypoeutectic Al-7.0 wt% Si alloy against gravity direction in a cylindrical mold with cross-sectional change was made, and the macrosegregation in different parts of the as-solidified sample was investigated (Ghods et al. in J Cryst Growth 441:107–116, 2016; J Cryst Growth 449:134–147, 2016). The current study is to use a two-phase columnar solidification model to analyze the segregation mechanisms as used in this experiment. Following flow phenomena and their contributions to the formation of macrosegregation are simulated and compared: (1) solidification shrinkage-induced feeding flow; (2) thermo-solutal convection; and (3) combined thermo-solutal convection and shrinkage-induced feeding flow. The shrinkage-induced feeding flow leads to an inverse (positive) segregation in the bottom part, and a severe negative segregation in the part below cross-sectional change. Thermo-solutal buoyancy leads to a so-called steepling convection in the main part of the sample (away from the bottom and cross-sectional change), and this kind of flow leads to a positive macrosegregation near the sample surface. The calculations have successfully explained the experimental result of macrosegregation.

AB - A unidirectional solidification experiment of hypoeutectic Al-7.0 wt% Si alloy against gravity direction in a cylindrical mold with cross-sectional change was made, and the macrosegregation in different parts of the as-solidified sample was investigated (Ghods et al. in J Cryst Growth 441:107–116, 2016; J Cryst Growth 449:134–147, 2016). The current study is to use a two-phase columnar solidification model to analyze the segregation mechanisms as used in this experiment. Following flow phenomena and their contributions to the formation of macrosegregation are simulated and compared: (1) solidification shrinkage-induced feeding flow; (2) thermo-solutal convection; and (3) combined thermo-solutal convection and shrinkage-induced feeding flow. The shrinkage-induced feeding flow leads to an inverse (positive) segregation in the bottom part, and a severe negative segregation in the part below cross-sectional change. Thermo-solutal buoyancy leads to a so-called steepling convection in the main part of the sample (away from the bottom and cross-sectional change), and this kind of flow leads to a positive macrosegregation near the sample surface. The calculations have successfully explained the experimental result of macrosegregation.

KW - Directional solidification

KW - Fluid flow

KW - Macrosegregation

KW - Shrinkage

UR - http://www.scopus.com/inward/record.url?scp=85054907962&partnerID=8YFLogxK

U2 - 10.1007/s12666-018-1422-9

DO - 10.1007/s12666-018-1422-9

M3 - Article

AN - SCOPUS:85054907962

VL - 71.2018

SP - 2639

EP - 2643

JO - Transactions of the Indian Institute of Metals

JF - Transactions of the Indian Institute of Metals

SN - 0972-2815

IS - 11

ER -