Formation of Fe-rich intermetallic compounds and their effect on the tensile properties of squeeze-cast Al-Cu alloys

The development of high performance Al-Cu based alloys generally depends on the strict control of the Fe content. However, with the increasing use of recycled aluminum alloys, it is necessary to increase the tolerance for the Fe content in Al-Cu cast alloys for the purpose of low cost, energy saving, and environment protection. In this study, the formation of Fe-rich intermetallics and their effect on the tensile properties of squeeze-cast Al-5.0 wt% Cu-0.6 wt% Mn alloys with an Fe content of up to 1.5 wt% have been investigated. The full formation sequence of squeeze-cast Al-5.0 wt% Cu-0.6 wt% Mn alloys with different Fe contents has been established. The results were also compared with the corresponding results obtained for Al-5.0Cu-0.6Mn alloys prepared by gravity die casting. It is found that the Fe-rich intermetallic compounds mainly consist of alpha-Fe and beta-Fe in alloys with a low Fe content, changing into Al-6(FeMn) and Al-3(FeMn) for alloys with a high Fe content. The applied pressure promotes the formation of the Fe-rich intermetallics alpha-Fe/Al-6(FeMn) and prevents the precipitation of needle-like beta-Fe/Al-3(FeMn). The elongation of the alloys gradually decreases with the Fe content, and a maximum value for both the ultimate mechanical strength and the yield strength was found for the alloys with 0.5 wt% Fe. The tensile properties of alloys with a different Fe content significantly increased as the applied pressure was increased from 0 to 75 MPa, especially the elongation.