A prediction of Fe-Al IMC layer thickness in TIG-assisted hybrid friction stir welded Al/steel dissimilar joints by numerical analysis

In joining aluminum alloy to steel, excessive growth of Fe-Al intermetallics (IMC) can deteriorate the joint quality with its brittleness by low solubility of liquid aluminum in iron. This problem can be fixed by adopting a solid-state welding such as friction stir welding (FSW), but lack of plastic flow and excessive tool wear are limitations during the process. In this study, joining 2.5 mm thick Al5052 aluminum alloy to 1.4 mm thick DP590 high strength steel was proceeded by TIG-assisted hybrid friction stir welding (HFSW) to improve the plastic flow and to decrease plunging force on the FSW tool. The purpose of this study is to realize the effect of preheating source on the growth of IMC layer thickness based on the 3D heat transfer numerical model. Thermal characteristics and IMC layer thickness on the welded joints were estimated and validated with experimental results. Consequently, HFSW adopting 20 A TIG current achieved the highest average tensile strength as 184 MPa with 2.39 μm IMC layer thickness, and the numerical result showed a fair agreement to the experimental results. It is realized that the heat generation per unit length of the time significantly influences on the maximum temperature and the growth of IMC layer thickness.