Effect of Cooling Rate on Iron-rich Intermetallic Phases in 206 Cast Alloys

The effect of cooling rate on the solidification characteristics of the iron-rich intermetallics in 206 cast alloys with iron contents up to 0.5 wt% was investigated. The iron-rich intermetallics were analyzed and characterized by using Scanning Electron Microscopy (SEM), Differential Scanning Calorimeter (DSC) and Thermal Analysis (TA). It was found that Chinese script α-Fe and platelet β-Fe phases are the two main iron-rich intermetallics up to 0.3 wt% Fe. With increasing cooling rate, the precipitate temperature increases for a-Fe but decreases for β-Fe and eventually the formation of the β-Fe will be completely suppressed. At 0.5 wt% Fe, two extra iron-rich intermetallics, Chinese script Al_m(FeMn) and platelet Al₃(FeMn) are experimentally observed. With increasing cooling rate, the Al₃(FeMn) or Al₆(FeMn) phases that precipitated at relatively low cooling rate can be replaced by Al_m(FeMn) and α-Fe. The critical cooling rate to effectively suppress the formation of the platelet β-Fe and obtain dominant Chinese script α-Fe or Al_m(FeMn) decreases with increasing iron level.