Microstructure and properties evolution of Al–17Si–2Fe alloys with addition of quasicrystal Al–Mn–Ti master alloy

Abstract

The Fe-rich intermetallic compounds in Al–17Si–2Fe were modified via Al–Mn–Ti quasicrystal master alloy. The effect of master alloy content on the Fe-rich phase morphology was studied by scanning electron microscope (SEM) and thermodynamic calculation. Results show that the microstructure of the Al–Mn–Ti master alloy consists of binary quasicrystal matrix and ternary AlMnTi secondary phase. The evolutive tendency of Fe-rich intermetallic compounds with content of quasi-crystal Al–Mn–Ti master alloy increasing can be described as follows: long needle-shaped β phase for Al–17Si–2Fe alloy, long plate-shaped ternary δ phase for 3 wt% master alloy addition, Chinese-script and polyhedral α phases for 4 wt% master alloy addition and finer plate-shaped quaternary δ phase with α phases for 5 wt% master alloy addition. The ultimate tensile strength of the Al–17Si–2Fe alloy with 4 wt% master alloy addition (a mass ratio of wMn/wFe ≈ 0.7) increases by 23.8% and the friction coefficient decreases from 0.45 to 0.35 compared with those of Mn-free alloy. α-Fe phases have less negative effect on the matrix compared with the long needle-shaped β phase and the plate-shaped δ phase.