This paper deals with the tool plunge stage of friction stir welding which precedes the formation of the T-joint. A three-dimensional numerical model, developed in software package Simulia Abaqus® is applied for numerical analysis. The material of the welding plates is high strength aluminium alloy 2024-T3 of 3 mm thickness. The change of thermomechanical conditions in the welding zones has been analysed, as well as the conditions for eliminating the joining line in the weld root. The tool rotation speed and shoulder plunge depth are varied. Two tools are used for analysis with different tool pin lengths: 2.6 mm and 3 mm. Increase in tool rotation speed raises the temperature in the welding zone and creates conditions for eliminating the joining line in the weld root. In addition, the increased tool pin length is also beneficial. It is obtained that the tool rotation speed exceeding 500 min–1 is necessary for this joint and tool geometries.

The numerical simulation of friction stir welded T-joints made of AA2024 T3 is investigated. Analysis of heat generation due to friction and plastic work is performed, as well as of the reaction force in the normal direction during the plunge stage of the friction stir welding. The effect of joint geometry is studied for butt joints and T-joints produced from the same material. Different tool rotation speeds and tool pin lengths were considered forT-joint friction stir welding. It was shown that the temperature at the root of the weld below the tool pin is lower in the T-joint than in the butt joint, due to the efficient conduction of the heat produced through the normal plate. Also, the reaction force was higher for the T-joint than for the butt joint, so, heat production by friction was more intense in comparison with the heat produced by plastic deformation. The reaction force was moderately increased for the tool with a shorter pin, increasing both components of the heat produced. An increase in the tool rotation speed decreased the resistance to the tool plunging into the T-joint, increasing the frictional heat and decreasing the amount of heat generated by plastic deformation.