Effect of Defects at the Root of the Joints of 1901T Alloy Plates Made by One-Sided Friction Stir Welding on Their Mechanical Properties

The effect of the defects having formed during one-sided friction stir welding of alloy 1901 plates in the weld root on the mechanical properties of the formed butt joints is studied. Defects in the form of incomplete fusion and oxide film aggregates 0.1–0.3 mm in size in the weld root are detected using X-ray computed tomography and microstructural analysis of the joints using optical microscope. The presence of defects in the root of the joint of alloy 1901T plates leads to a decrease in their strength coefficient from 0.85 to 0.74. In this case, the fracture of the joint during static tensile tests shifts from the heat-affected zone to the mixing zone. The fracture of samples during static tension is initiated by incomplete fusion (oxide film) in the weld root with characteristic brittle fracture and then spreads into the mixing zone metal. The fracture becomes ductile with oxide film islands mixed into the weld on welding. The incomplete fusion and oxide films in the weld root halves the bending angle. A necessary condition for eliminating incomplete fusion in the root of the butt joint of alloy 1901T plates is the equality of the working pin length and the thickness of the workpieces to be welded with allowance for the immersion of the tool shoulder into the metal to be welded.