Identification of a pseudo-ternary intermetallic compound in the stirred zone of friction-stir-welded 5083 aluminum alloy with 316L steel

Macrostructure, microstructure, and distribution of phases through the interface were analyzed for friction-stir-welded joints 5083 aluminum alloy and 316L steel. Several analytical techniques, including light microscopy, transmission and scanning electron microscopy, elemental analysis using X-ray spectroscopy, and electron diffraction, were used to thoroughly analyze the weld interface. The interface is characterized by a significant reduction in grain size for both aluminum alloy and stainless steel. New compounds, not corresponding to thermodynamically stable phases in the binary Al-Fe phase diagram, were found in the stirred zone (SZ) as dispersed particles. On the steel side of the welding, thin slabs of new compounds were found, as well, being interlaced with the stainless steel. The observations support that the grain refinement of stainless steel is likely due to a continuous dynamic recrystallization. The intermetallic compounds present as a layer at the interface, exhibiting nanometric grain size, were identified by electron diffraction as Al13Fe4 and Al5Fe2 phases. Concerning the intermetallic compound formed in SZ, the elemental analysis showed a compound containing principally Al and Fe, with admixture of Si and Mn. It was concluded that it is a pseudo-ternary compound with body-centered cubic structure, Im-3 space group, which is for the first time reported in this kind of dissimilar assembly, and is known as alpha-Al(Fe,Mn)Si.