Plitchenko S. Determination of the influence of energy-power parameters of friction stir welding technology on structural transformations in the joint zone

The purpose of the work is to substantiate the choice of energy-power parameters of friction stir welding technology of AMg aluminum alloys by structural transformations in the weld zone. The object of research - the processes of welding alloys without changing the physical state. The subject of research is the processes of structural transformations in AMg alloys during friction stir welding. Research methods: to study the processes of structural transformations in the development of proposals for improving the technology of friction stir welding of aluminum alloys used techniques for measuring temperature, estimating thermal energy and the force of pressing the tool to the workpiece. The methods of microstructural and X-ray diffraction analysis are used in the work to determine the mechanical properties (tensile, hardness and microhardness). The dissertation presents a new solution of the current scientific and technical problem of choosing the parameters of friction stir welding of AMg alloys based on the analysis of structural transformations under the action of a tool that provides high quality welded joints. The rationality of increasing the speed of rotation of the tool (up to 1600 rpm) by reducing its clamping force (up to 580 N) according to the calculations of the activation energy of the transition of AMg5 alloy (when connecting plates with a thickness of 1.85 mm) to the superplastic state. It is established that at welding temperatures of 0.7 ÷ 0.8 of the solidus temperature of the AMg alloy, it is possible to control the processes of accumulation of structure defects and their annihilation by varying the energy-power parameters (pressing 275 N and rotational speed 1600 rpm). For the first time, a method was developed and implemented to determine the optimal ratio of energy-power parameters, the radius of the tool shoulder and the thickness of the welded sheet AMg, which provides improved mechanical properties of the welded joint.