| Summary: | The volume of fluid (VOF) modeling method was implemented to simulate the underwater friction-stir welding (FSW) process for dissimilar joining between aluminum and steel. Temperature profile, materials flow, and intermixing during dissimilar bonding under the cooling medium were monitored via VOF modeling and verified according to experimental data. The effects of processing parameters on the formation of intermetallic compounds (IMCs) at the Al/St interface, microstructural characteristics, and mechanical property of dissimilar weldments were studied and addressed. By decreasing tool rotational speed (w), increasing traverse velocity (v), and employing cooling medium, peak temperature continuously reduced (down to ∼473 and 573 K for the aluminum and steel sides, respectively) led to substantial refining the grain structure and formation of a thinner IMC layer. The average grain size in the aluminum and steel sides of SZ is refined down to ∼4 and 12 µm, respectively. The thickness of the IMC layer varied depending on the processing parameters with the lowest value of ∼0.2 µm. The formation of a curved interface due to enhanced materials mixing at the advancing side is noted with a linear hardness gradient across the dissimilar weldment. Superior mechanical strength of ∼80 MPa attained at an optimized submerged condition of w = 1650 rpm/v = 40 mm/min showed combined ductile-brittle fractographic aspects on the fracture surface.
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