Friction stir butt-welding of roll cladded aluminum thin sheets: effect of microstructural and texture changes on mechanical properties

Experimental studies are carried out on the friction stir butt-welded aluminum (Al)-clad-aluminum thin sheets. Aluminum alloy 4343 (AA4343, Al–Si series) and 3003 (AA3003, Al–Mn series) act as the clad layer and the core of the Al-clad-Al material system, respectively. Optical microscopy confirms that the joining is achieved successfully without macroscopic defects, while the clad layer is mixed into the core, mostly in the advancing side (AS) of the stir zone (SZ). Outside the SZ, no delamination between the clad layer and core is observed. Material flow analysis with electron probe microanalyzer exhibits the flow of silicon (Si) particles from the clad layer to the core resulting in several Si-induced precipitations of α-Al(Fe, Mn)Si, α-AlMnSi inside the SZ. The heterogeneous distribution of those precipitates is visualized by scanning electron microscopy and their compositions are analyzed using an energy dispersive X-ray spectrometer. Electron back-scattered diffraction maps reveal dynamically recrystallized ultra-fine grain structures (3.7–3.9 μm) inside the SZ. The mechanical properties of the joint are evaluated by cross-sectional 2D microhardness mapping and uniaxial tensile tests. Inside the SZ, the grain refinement with the formation of Si precipitation increases the tensile strength and microhardness of the joint.