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

Abstract

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 Alm(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 Alm(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 Alm(FeMn) decreases with increasing iron level.