Enhancement of mechanical performances via a novel post-weld friction stir rolling technique for friction stir welded 2195 Al-Li alloy joint

To improve the strength of friction stir welded (FS-welded) joints of 2195 Al-Li alloy, an innovative friction stir rolling (FSR) technique after friction stir welding (FSW) was proposed by the present research. In order to explore the affecting mechanism of FSR on FS-welded joint, a detail investigation was conducted on the microstructural evolution and mechanical properties of the joints subjected to FSR. The results reveal that applying the post-weld FSR treatment on both sides of weld introduces a rolling zone (RZ) in the joint. Compared with the region to be rolled in the FS-welded joint, the corresponding RZ exhibits finer grain size, higher proportion of deformed grains, and increased dislocation density in the friction stir rolled (FS-rolled) joint. Furthermore, second-phase particles in the RZ are refined and present a more dispersed distribution. Mechanical testing demonstrates a clear enhancement in joint strength after FSR. Especially, there is a good trade-off between strength and ductility when a proper rolling condition is selected. A combination of 422.6 MPa tensile strength and 6.9% elongation is achieved at a tool traversing speed of 200 mm/min. The uniformly dispersed fine second-phase particles and grain refinement are essential reasons for the strength and elongation increments of the FS-rolled joints. The present study provides a technological approach and a theoretical foundation for the FSR technique used in light-weight manufacturing field.