Effect of Mn, Si, and Cooling Rate on the Formation of Iron-Rich Intermetallics in 206 Al-Cu Cast Alloys

The solidification structures of commercial 206 Al-Cu cast alloys with 0.15 pct Fe have been studied using thermal analysis (TA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and electron backscattered diffraction (EBSD). The EBSD results have shown that there are two iron-rich intermetallics: Chinese script α -Fe and platelet-like β -Fe. The addition of either Mn or Si has helped to promote the formation of α -Fe and hinder the precipitate of β -Fe. The combined addition of both Mn and Si is even more effective than the individual addition of either Mn or Si. The full solidification sequence of the 206 cast alloy has been established. The volume percent and formation temperature increase for α -Fe but decrease for β -Fe with increasing cooling rate. The platelet β -Fe can be effectively suppressed in 206 cast alloys by controlling the alloy chemistry and cooling rate. A casting process map is proposed to correlate the Mn and Si contents with cooling rates for the 206 cast alloys.