Formation of nanoscale reaction layer with several crystallinities in the friction-welded 6061 Al alloy/steel joint

Abstract

Through precise control and manipulation of welding parameters for inertia friction-welded Al alloy/steel joints, the transformation of nanoscale interfacial layer from the amorphous to the mixed phase (co-existence of amorphous and crystallised phases) and then to a fully crystallised Fe2Al5 intermetallic compound (IMC) was observed. The temperature and velocity range for the formation of different phases, including amorphous phase, mixed phase and IMC was exploited. A high level of plastic deformation and flow was found to destabilise the crystallised Fe-Al structure, promoting the formation of amorphous phase and enlarging the formation window of amorphous and mixed phase at a high temperature (∼650 K). The processing temperature was expected to govern the crystallinity of the final interfacial microstructure. The joint failed at the Al alloy side when an amorphous or mixed phase appeared at the interface, but a thicker (>100 nm) IMC layer resulted in a significantly decreased strength. The present study may provide insight on the analysis of the interfacial reaction at the initial stage of friction-based solid-state welded Al alloy/steel, and on controlling the resulting properties.