Analysis of microstructure and mechanical properties of the aluminum alloy T-joint welded by stationary shoulder friction stir welding

2219C10S aluminum alloy T-joint was successfully performed by stationary shoulder friction stir welding. The weld surface is smooth and has no obvious thickness-reduction. The PAUT testing on the back of the substrate plate shows that all the surfaces between the substrate and rib plates were welded thoroughly. The macro-structure revealed two weld contours symmetrically distributed in the center of the rib plate. The unilateral weld contours also exceeded the center line of the rib plate. The microhardness distribution of the joints shows a unique U-shaped distribution, and the microhardness of the weld nugget zone was the lowest. The crack of tensile specimens with the two directions of T-joint initiated at the tangent of the tension plate and the corner of the joint R1. However, the transverse areas of the fracture surface for the two types of tensile specimens are quite different. This is the main reason why the tensile strength along the direction of rib plate was 20 MPa lower than that along the direction of the substrate plate.