Intermetallic compounds (IMCs) formation during dissimilar friction-stir welding of AA5005 aluminum alloy to St-52 steel: numerical modeling and experimental study

Abstract

In this research, AA5005-O aluminum-magnesium alloy and St-52 low carbon steel sheets were friction-stir welded in a butt-dissimilar joint design. Effects of different processing parameters including tool rotational speed (w), traverse velocity (v), plunge depth, and offset distance on the solid-state weldability of these dissimilar materials were assessed in terms of formation of intermetallic compound (IMC) layer at the interface. A 3D thermo-mechanical finite element modeling procedure was employed to predict the nucleation and growth of IMC layer. Formation of various FeAl, FeAl3, and Fe2Al5 IMCs at the interface, layer morphology, and thickness were experimentally studied as well, by using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) analysis techniques. A good agreement between the simulated thermal results and experimental data was noticed. The results showed that the thickness of IMC layer at the interface as the main controlling parameter in transverse tensile property and fracture behavior of produced dissimilar joints can be varied extremely as a function of processing parameters. By decreasing the heat input and suppressing the kinetics of IMCs layer formation, the tensile performance of dissimilar welded joints is improved, considerably. However, the soundness of these dissimilar welds played another main role as a restriction mechanism against this trend. The maximum joining efficiency is attained around 90% at an optimized working window of w = 1200 rpm, v = 90 mm/min, and a plunge depth of 0.3 mm with an offset distance of 0.5 mm toward the Al side. The hardness of this optimized dissimilar weld is enhanced even more than the steel base metal caused by the formation of IMC layer at the interface as well as the dispersion of reinforcing intermetallic particles (IMPs).