Highly stable nanoscale amorphous microstructure at steel-aluminum interface enabled by a new solid-state additive manufacturing method

Abstract

In contrast to the established understanding that the interfacial microstructure of the bonded steel-aluminum (Fe-Al) structures coarsens significantly at elevated temperatures, this study shows that the special nanoscale interfacial layer of the Fe-Al bimetallic structures fabricated by a newly developed modified friction stir additive manufacturing (M-FSAM) exhibited extraordinary stability up to 500 °C. In tensile tests, the heat-treated Fe-Al samples failed within the aluminum alloys rather than along the Fe-Al interface. The heat treatment at 500 °C did not cause any observable microstructure change in the special nanoscale interfacial layer, which still consisted of a noncontinuous layer of Al-Fe-Si particles and a continuous Mg and O rich layer. The noncontinuous Al-Fe-Si particles were made of an amorphous-like microstructure and the Mg and O rich layer was comprised of an amorphous matrix interspersed with nanocrystalilne particles.