Effect of Microstructural Changes by Friction Stir Processing on the Clad-to-Core Interfacial Strength of Thin Aluminum-Clad Aluminum Sheets

The present study successfully utilizes friction stir processing (FSP) as a surface engineering tool on an AA4343-clad AA3003 sheet to improve the interfacial strength through microstructural homogenization. Compared to the base material condition, electron back-scattered diffraction analysis after FSP reveals a considerable reduction in grain morphological disparity between the clad layer and the core due to the occurrence of grain refinement by continuous dynamic recrystallization. Scanning electron microscopy (SEM) analysis reveals various Si-induced precipitations, including Al (Mn, Fe) Si, within the stir zone due to the diffusion of Si from the clad layer to the core during FSP. The influence of microstructural changes on improving the mechanical properties of the bi-layer clad sheet is also examined. The surface microhardness values of the clad (~ 28.7 Hv) and core (~ 35.5 Hv) for the base material condition are found to be improved to ~ 34.7 Hv and 38.5 Hv, respectively, after FSP. Besides, the overall strength of the FSPed clad sheet increases by ~ 45% compared to the base material conditions. The microstructural homogenization and Si-induced precipitates act together to strengthen the interface in the clad material system. SEM images on the fractured surfaces of the tensile specimens reveal delamination between the AA4343 (clad layer) and AA3003 (core) for the base material condition, which disappears after FSP.