Interfacial reaction in steel–aluminum joints made by friction stir welding

The reaction layers of friction stir welded joints made from austenitic stainless steel and Al alloy consisted of mixed layers of elongated and ultra-fine grains and the intermetallic compound layer. The intermetallic compound layer was identified as Al4Fe with a hexagonal close-packed structure and a thickness of approximately 250 nm. The elongated grains were shown to consist of a ferrite phase because of their ferromagnetism and a body-centered cubic crystal structure.