Distribution of intermetallic compounds in dissimilar joint interface of AA 5083 and HSLA steel welded by FSW technique

Abstract

Multi-material design concept is growing rapidly in association with the advancement of dissimilar alloy joining technology implementing FSW technique. In this paradigm, the major concern in joining Al alloys to steel by FSW technique, is to manage the intermetallic layer formation. In this context, knowing the types of Al-Fe series IMCs and their distribution is an important aspect for determining the joint performance. The present research thoroughly examined the interface region of the dissimilar welded joint between AA5083 and HSLA steel fabricated by FSW technique in butt configuration. The joint interface was deeply investigated by XRD, EBSD, TEM and APT studies to explore the distribution pattern of the various type of Al-Fe intermetallic compounds across the joint thickness. The study identified from the inverse pole figure (IPF) maps the presence of Al rich IMCs Al6Fe and Al13Fe4, in Al side and Fe rich phases AlFe and AlFe4 in steel side. A massively recrystallized microstructure with ultrafine grains of order ∼1 μm in diameter and a misorientation of 0.82 high angle grain boundary (HAGB) fraction were observed at the interface along with the aforesaid IMCs. Overall, the EBSD along with TEM study depicted that the distribution of Al13Fe4, Al5Fe2, Al9Fe2 and AlFe intermetallic in the microstructure of the interface mainly due to the typical CDRX and DDRX process occurs during FSW. The dominance of HAGBs are found to be the potential factor for diffusion of Fe in Al and vice-versa and which in turn influenced the type and distribution of IMCs across the interface. Moreover, the APT data analysis was successful to explain the atomic mixing pattern by the FSW process and typically Fe rich fragments of AlFe IMC phase was discovered from the reconstruction image and the proximity histogram.