Effect of Defects in the Root Part of One-Sided Friction Stir Welding Joints in 1901T Alloy Plates on Mechanical Properties

The results are presented for impact of defects formed during one-sided friction stir welding plates made of alloy 1901 in the root part on the mechanical properties of resulting butt joints. The defects are represented by the lack of fusion and accumulations of oxide films in the root part of the joint. The defect length is 0.1–0.3 mm and the defects are detected using computer X-ray tomography and analyzing the microstructure of the joints using an optical microscope. The defects present in the root part of the plate joints made of alloy 1901T result in decrease in the welding factor from 0.85 to 0.74. The area of the joint break during a static tensile test shifts from the heat-affected zone to the stir zone. The break of the samples exposed to static tension is initiated by a lack of fusion (the areas occupied by oxide films) in the root part of the joint with a characteristic brittle fracture propagating into the stir zone. The fracture becomes ductile with islands of oxide film entering the weld during the welding process. The presence of the lack of fusion and oxide films in the root part of the joint results in a 2-fold decrease in the joint bending angle. A necessary condition for eliminating the lack of fusion in the root part of the butt joint in plates made of alloy 1901T deals with making the length of the rod (pin) of the working tool equal to the thickness of the workpieces welded, taking into account the degree of immersion of the tool shoulder in the weld metal.