Effect of Main Parameters of the Friction Stir Welding on Structure Imperfections of Welded Joint

Purpose: to identify the fracturing behavior of the defected aluminum-magnesium alloy friction stir welded joints. The paper presents the results of analysis of varieties of structural defects in a welded joint and its effect on the strength of welded joints under static tension. The brief review of the main reasons for the appearance of discontinuities in the structure of the welded joint is given; the influence of the main parameters of the temperature regime in the welding area on obtaining a high-quality weld is evaluated. In accordance with the fractographic analysis of the fracture surface of samples with welded joint and layer by layer metallographic analysis of the material in the defect zone, the types of defects specific for friction stir welding are described and the nature of its origin is discussed. The obtained results indicate the defining role of the nature of the plastic flow of material in the zone of the moving tool in the formation of the structure and properties of the welded joint and can be taken into account when choosing friction stir welding modes and welded joints quality control. Methods: experimental studies were carried out on a laboratory machine for friction stir welding, manufactured by ISPM SB RAS. Static tensile tests were performed on tension testing machine UTS110M-100. Structural studies were performed by optical and scanning microscopy using the MiniSEM electronic scanning microscope. Results and Discussion: the effect of the welding process main parameters on the quality of welded joints is shown on the example of Al 5083 alloy plates of different thicknesses. It is shown that the welding regime determines the type and size of the defects formed, the mechanical strength and the nature of the welded joints fracture mode. According to the comparative analysis of the fracture surface of samples after static tensile tests, it is found that in the defect zone the fracture mode is changed from the viscous nature to the brittle one. The forming features of defected structure of the welded joint are revealed by varying the heat input value. It is shown that not the thickness of the welded plates affects the type of defect formed, but the amount of heat input into the welding zone. Based on the results of fractographic analysis of the welded joints fracture surface and layer by layer metallographic analysis of the material in the defect area, types of defects specific for friction stir welding are described and the nature of its origin is discussed.

friction stir welding, aluminum alloy, structural defects, tensile strength, fracture