Overcoming the strength-ductility trade-off in additive manufactured AlSi10Mg plates by friction stir welding at a low rotational speed

The main problem in post-treatment of laser powder bed fusion (L-PBF) AlSi10Mg is the sharp reduction in strength when the ductility enhances, i.e. the problem of strength-ductility trade-off. Friction stir welding (FSW) at a low rotational speed of 200 rpm was employed to join AlSi10Mg plate produced by laser-powder bed fusion in conjunction with overcoming the strength-ductility trade-off. The microstructure, texture, and mechanical properties of the as-built and friction stir welded samples were examined. FSW resulted in the elimination of porosities, formation of ultrafine-grains with an average grain size of 0.7 μm, increment in dislocation density and Taylor factor, and fragmentation of Si particles. In addition, after FSW, B/B¯ and C shear texture components were mainly formed in the center of the stir zone, while at the shoulder-dominated zone the A₁^∗(111)[1¯1¯2] and A₂^∗(111)[112¯] components might be formed. The main grain structure formation mechanism was continuous dynamic recrystallization occurring by a gradual increase in misorientation of low angle grain boundaries and geometrically dynamic recrystallization. Consequently, tensile elongation was enhanced by ≈173%, while a negligible decrease in strength (≈9%) was observed. During tensile loading, the joint was fractured from the stir zone by the initiation of cracks from the surface of the sample, resulting in a bimodal dimple structure.