Predicting the quantity and type of intermetallic phases in aluminum-steel dissimilar joints produced by zinc interlayer

In this study, the formation of brittle intermetallic compounds in over-lap joints of 1100 aluminum and low-carbon galvanized steel made by gas-tungsten arc welding method was investigated. The welding process was simulated by finite-element method, and temperature histories during the welding process were derived from it. The Gibbs-free energy of Fe-Al and Fe-Zn intermetallic phases was calculated, and their formation was predicted by means of thermodynamic modeling. The growth behavior of IMCs at the interface of the joint was studied through optical and scanning electron microscopy and energy-dispersive X-ray spectroscopy. A relation was provided to predict the thickness of the formed compounds at the interface. The modeling results revealed the formation of FeAl3 and Fe2Al5 compounds, which were consistent with the experimental results. Studying the compound growth behavior proved that the zinc coating on galvanized steel can act as an interlayer to delay and limit the growth of intermetallic compounds at the interface. The thickness of the intermetallic layer in samples welded with 100A and 110A currents was 6.2 and 10.2 mu m, respectively, which was reduced by an average of 70% compared to the conditions without the presence of the zinc interlayer.