Mechanistic understanding on the evolution of nanosized Al3Fe phase in Al–Fe alloy during heat treatment and its effect on mechanical properties

Abstract

Al–1Fe (wt%) alloy containing nanosized Al3Fe phase was processed by continuous rheo-extrusion, and subjected to heat treatment at different temperatures. During heat treatment, due to the diffusion of Fe atoms, the nanosized Al3Fe phase was blunted and fragmented along the width direction, and the bluntness and fragmentation resulted in the spheroidization of Al3Fe phase. However, with the extension of heat treatment time, the spheroidized Al3Fe phase became coarse and grew along a particular plane. Then, the morphology of Al3Fe phase transformed into small plate-like. While, the plate-like Al3Fe phase with an average length of 30 µm in the as-cast Al–1Fe (wt%) alloy indicated good thermal stability during heat treatment. The different thermal stability of Al3Fe phases was attributed to their size. The large surface curvature of nanosized Al3Fe phase significantly accelerated the diffusion of Fe atoms. When the heat treatment temperature was 200 ℃ and 300 ℃, the tensile strength and elongation of the rheo-extruded Al–Fe alloy marginally decreased. The decrease of tensile strength and the decrease of elongation increased when the heat treatment temperature was greater than 400 ℃. The tensile strength and elongation of as-cast Al–1Fe (wt%) alloy were insignificantly altered. Though the loss of tensile strength of Al–Fe alloy containing nanosized Al3Fe phase was much greater, its tensile strength was always higher than the tensile strength of the as-cast Al–Fe alloy in the entire heat treatment.