Friction stir welding of additively manufactured A20X aluminum alloy: welding process, mechanical properties, and microstructure

A20X is an advanced and high-strength additive manufacturing aluminum alloy with promising applications in several fields, including aerospace and aeronautics. However, its assembling through fusion welding technologies poses challenges due to the detrimental effects of melting and solidification. Friction stir welding offers a promising solution for joining A20X, producing components with superior mechanical properties while preserving the engineered microstructures. This study investigates the influence of friction stir welding on the quality of butt joints made of 4 mm thick additively manufactured A20X plates produced by laser powder bed fusion. Different rotational (900 and 1500 rpm) and welding speeds (100 and 500 mm/min) were tested to evaluate the influence of the joining process on weld quality (mechanical strength, microstructures, welding defects, and surface roughness). Friction stir welding maintains a very fine microstructure in the welds, with only a slight reduction of the mechanical strength compared to the base material (335 MPa vs. 385 MPa on average). The hardness of the welded joints increases, attributed to local aging caused by the heat input during the joining process. Lower tool rotation and welding speed result in tunnel defects, notably reducing joint strength. 3D X-ray computed tomography reveals that the metal stirring occurring during the joining process notably reduces the intrinsic porosity of A20X. It also breaks up Ti borides and promotes the growth of Al-Cu precipitates within the stir zone. The fractographic analysis highlights the ductile behavior of A20X after welding, emphasizing the critical role of welding parameters in joint integrity.