Transient microstructural evolution of infrared brazed Fe 3Al intermetallics using aluminum foil

Abstract

The present work reports a novel approach in joining Fe 3Al by infrared brazing using the pure Al as brazing filler metal. Based on the Al–Fe binary alloy phase diagram, the species and morphology of phases as well as the transient evolution of microstructures in the infrared brazed joint are extensively studied. The Fe 3Al substrate is dissolved into the molten braze, and reacts simultaneously with the Al-rich melt during infrared brazing. Various iron aluminides such as FeAl 3, Fe 2Al 5, FeAl 2, FeAl and eutectoid FeAl 2–FeAl are observed in the infrared brazed joint for different brazing temperatures. For brazing temperatures between 700 and 1000 °C, the dendritic morphology of Fe 2Al 5 phase dominates the infrared brazed joint. For brazing temperatures between 1050 and 1200 °C, solid-state interdiffusion of aluminum and iron among reaction products and base metal is followed by isothermal solidification of the molten braze. Primary FeAl and eutectoid FeAl–FeAl 2 are widely observed in the infrared brazed joint. Further increasing the brazing temperature and/or time, the interface between the braze alloy and substrate is finally disappeared.