A quantitative study of the solute diffusion zone during solidification of Al-Cu alloys via in-situ synchrotron X-radiography and numerical simulation

Abstract

The solute diffusion zone plays a critical role in determining nucleation efficiency during heterogeneous nucleation. In this study, in-situ synchrotron X-radiography and numerical modeling were employed to investigate the Solute Suppressed Nucleation Zone (SSNZ) surrounding growing equiaxed grains in Al-13Cu alloys. Quantitative analysis of SSNZ and constitutional undercooling was conducted using image processing techniques. Solute concentration and SSNZ length in the direction exceed those in the direction, suggesting higher solute enrichment in dendrite centers. This causes greater undercooling in the dendrite growth direction () with faster dendrite growth rates. As equiaxed dendrites grow, SSNZ length in the direction decreases while increasing significantly in the direction. Utilizing data obtained from numerical simulations, we refined the analytical equation governing solute distribution preceding the solid–liquid interface under three-dimensional conditions, and the computational equation determining the SSNZ length. The SSNZ lengths derived from the optimized equation along the and directions demonstrate more agreement with both experimental observations and numerical simulation outcomes. Higher growth rates rapidly increase undercooling, limiting the development of nucleation-free zone. Additionally, SSNZ area growth slows at higher cooling rate, correlating with increased solute concentration and reduced area in SSNZ.

Keywords

• Solidification
• Grain refinement
• X-radiography
• Numerical simulation
• Solute suppressed nucleation zone