Effect of Cooling Rate and Silicon Refiner/Modifier on Solidification Pathways of Al-11.3Si-2Cu-0.4Fe Alloy

Abstract

The solidification behavior of a complex Al-11.3Si-2Cu-0.4Fe alloy with separate additions of 0.85% bismuth (Bi), 0.42% antimony (Sb), and 0.04% strontium (Sr) and cooled at rates between 0.5 and 2°C/s was examined by using a combination of computer-aided cooling curve thermal analysis (CA-CCTA) and interrupted quenching tests. Results show that the sequence of phase formations is in the following order: dendritic Al, pre-eutectic Al₁₅(Fe,Mn)₃(Si,Cu)₂ and β-Al₅FeSi intermetallics, eutectic Al-Si, and post-eutectic Al₂Cu. Bi, Sb, and Sr additions had a significant effect on the onset of Al-Si and Al₂Cu phases, with Sr having the strongest effect by decreasing the nucleation temperature of Al-Si. On the other hand, Bi addition increased the solidification range. Nucleation temperature of primary Al and Al₂Cu phase increased as cooling rate increased. The coherency temperature decreased, and the fraction solid at the coherency point increased with increasing cooling rate. A relationship between solidification temperature range and fraction solid for each phase evolutions was observed.

Keywords:

• Aluminium
• Bismuth
• Intermetallic
• Solidification
• Thermal analysis