Formation features of a welding joint of alloy Ti-5Al-3Mo-1V by the friction stir welding using heat-resistant tool from ZhS6 alloy

Introduction. The technological process of fabrication products from titanium alloys is often complicated by low quality of welded joints during electric arc or gas-flame welding operations due to high residual stresses and deformations. An example of a successful solution to this problem is the development and implementation of such high-tech processes of metal joining as friction stir welding, which does not refer to the methods of fusion joining. Friction stir welding as an advanced technology is used to obtain joints of “soft” metallic materials, such as aluminum. For “hard” metallic materials, friction stir welding has been limited due to the high demands on welding tools. The aim of this work is investigation of the possibility of using a tool made of the nickel-based heat-resistant alloy ZhS6U in friction stir welding of the titanium alloy Ti-5Al-3Mo-1V. Results and discussion. Optical and scanning electron microscopy results revealed that the structure of the weld is typical of this type of welding, gradient, consisting of a heat-affected zone, thermo-mechanical affected zone and a stir zone with a fragmented structure. When varying welding parameters, it is shown that the defectiveness of the weld is affected to a greater extent by the axial load on the tool, which is caused by a significant difference in the thermal effect on the material. Metallographic analysis methods revealed dissolution of welding tool material fragments in the stir zone of the non-detachable joint. Fractographic analysis of the fracture surface shows that the fracture in the weld zone is ductile, although in this case there are brittle bridges. Varying the parameters of friction stir welding made it possible to obtain an indissoluble joint with at least 90 % of the strength of the base metal.