Effects of Mn and Cu Additions on Solidification Microstructure and High-Temperature Strength of Cast Al–Fe Binary Alloy

Abstract

In order to investigate the effects of Mn and Cu additions on solidification microstructure and high-temperature strength of cast Al–Fe alloys, we have fabricated various Al–Fe-based alloys with compositions of Al–1%Fe, Al–1%Fe–1%Mn, Al–1%Fe–1%Cu, and Al–1%Fe–1%Cu–1%Mn (mol%) solidified at different cooling rates (0.3 K·s⁻¹ and 145 K·s⁻¹). In the Al–1%Fe binary alloy, the coarsened θ-Al₁₃Fe₄ phase with a needle-shaped morphology was often observed in the furnace-cooled sample (0.3 K·s⁻¹), whereas the cast sample (145 K·s⁻¹) exhibited several elongated α phases surrounded by fine α/Al₆Fe eutectic microstructure. Such a solidification microstructure was observed in the cast Al–1%Fe–1%Cu alloy, whereas the Al₂₃CuFe₄ phase was locally formed in the finally solidified zone in the furnace-cooled sample. In the Al–1%Fe–1%Mn alloy, the Al₆(Fe, Mn) phase was formed regardless of the cooling rate. Finer α/Al₆(Fe, Mn) two-phase eutectic microstructure was almost entirely occupied in the cast sample. The fine eutectic microstructure was observed in the cast Al–1%Fe–1%Cu–1%Mn alloy as well. Compression tests for cast alloy specimens revealed that the Al–1%Fe–1%Cu–1%Mn alloy exhibited the highest strength level among the studied alloy specimens, indicating the combined addition of Mn and Cu elements could be effective in improving the high-temperature strength of the cast Al–Fe alloys.