Amorphous interfacial microstructure and high bonding strength in Al-Fe bimetallic components enabled by a large-area solid-state additive manufacturing technique

Abstract

There is a growing demand for the ability to manufacture large-scale aluminum-steel (Al-Fe) bimetallic components for realizing the enormous advantages of advanced multi-material structures which offers effective lightweighting and increasingly smart functionalities. The formation of brittle intermetallic compounds (IMCs) at the bonding interface has been the major barrier to safety-critical applications with existing manufacturing processes, including additive manufacturing techniques. This study showed that a combination of a novel modified friction stir additive manufacturing (M-FSAM) and pre-processing surface polishing of the stainless steel enables the formation of a relative homogenously distributed nanoscale amorphous layer along the bonding interface between the 6061 Al and the 304 stainless steel. As a result, the high interfacial bonding strength of 280 MPa was achieved. Compared to the existing friction stir welding/AM processes, M-FSAM enables a significant increase in tool traverse speed and a remarkable reduction in tool cost for Al-Fe bimetallic component manufacturing. The nanoscale amorphous layer consisted of a continuous O and Mg rich layer 10–20 nm in thickness and a discontinuous Al-Fe-Si layer 50–100 nm in thickness. The O and Mg rich layer consisted of an amorphous matrix with nanocrystalline precipitates while the Al-Fe-Si layer consisted of a q-glass with some degree of crystallinity. The formation mechanism of the unique Al-Fe interfacial microstructure was analyzed in detail in this study.