Al–Mn–Fe intermetallic formation in AZ91 magnesium alloys: Effects of impurity iron

The influence of iron on the formation Al–Mn–Fe intermetallic compounds (IMCs) has been investigated in solidification Mg–9Al-0.7Zn-0.2Mn (wt.%, AZ91) with contents ranging from ∼0.001 to > 0.01 wt.% Fe. Four IMCs formed depending Fe-content and location crucible: B2–Al(Fe,Mn), Al8Mn5, Al11Mn4 and, at bottom crucibles, Al5Fe2. four nucleated grew one another, producing multiphase particles. These usually contained numerous orientations that were all interrelated through simple orientation relationships are discussed terms similarities between IMC crystal structures. content affected phase fractions particle morphology. At low content, Fe-rich B2 was encapsulated by a low-Fe Al8Mn5 shell. With increasing phases (B2 Al5Fe2) gradually became direct contact α-Mg. threshold Fe:Mn for adequate corrosion performance is found correlate approximately where B2–Al(Fe,Mn) first becomes exposed α-Mg matrix.