Material Flow‐Induced Interfacial Microstructure and Surface Characteristics in Friction Stir Welded 304 Stainless Steel/2024‐T3 Al Alloys Tailor‐Welded Blanks

Tailor‐welded blanks (TWBs) of dissimilar alloys offer a promising route to lightweight, high‐performance structures, yet their reliability hinges on precise control of interfacial phenomena during joining. This study establishes a direct correlation between friction stir welding (FSW) speed and the resulting microstructure, material flow characteristics, and surface properties in TWBs fabricated from 2024‐T3 aluminum (Al) alloy and 304 stainless steel (SS304). Despite earlier investigations into dissimilar FSW, the coupled effect of welding speed on grain refinement, interfacial bonding, and tribomechanical performance remain underexplored. Through systematic variation in welding speed—from 40 to 20 mm min −1 , this work demonstrates enhanced thermal input and plastic deformation at lower speeds, reaching peak temperatures of 371.5 °C. Electron backscattered diffraction analysis confirms substantial grain refinement, with an average grain size of 4.2 ± 0.2 μm in stir zone. Tribological assessment reveals improved wear resistance, as wear rate drops from 4.56 × 10 −6 mm 3 Nm −1 to 3.69 × 10 −6 mm 3 Nm −1 , accompanied by a reduced wear track depth of 12.087 μm and smoother surface roughness of 0.512 μm. Microhardness peaks at 413 Hv due to the effective dispersion of steel fragments within an aluminum matrix enriched by intermetallic layers of FeAl 3 and Fe 2 Si.