## 1 Introduction  
Aluminum alloys are widely used in electrical appliances, ships, aerospace, transportation, and other industries. Aluminum alloys have the advantages of high specific strength, low density, corrosion resistance, good toughness, and good molding process, and are widely used in the high-end equipment manufacturing industry. As an important metal connection technology, welding is an indispensable processing technology in the production of structural parts. However, due to the characteristics of high thermal conductivity, low melting point, and high thermal expansion rate in the welding process of aluminum alloy, the traditional fusion welding process is prone to defects such as welding hot cracks, inclusions, porosity, alloy element burning, and welding residual deformation, which lead to a decrease in weld quality. Compared with fusion welding, friction stir welding has the advantages of solid state connection, lower production cost, and excellent joint performance in aluminum alloy welding [1; 2; 3; 4]. Friction stir processing (FSP) is a solid-state surface modification process, which causes severe plastic deformation, mixing of material, and lower temperature exposure, leading to significant microstructural refinement, densification, and homogeneity of the processed layer. Friction stir welding (FSW) uses high-speed rotating welding tools to heat the workpiece to make the material flow in a thermoplastic manner and realize weld forming under the forging action of the shaft shoulder [5; 6; 7; 8]. As a new green welding technology, 2A14-T6 aluminum alloy belongs to the Al-Cu-Mg-Si series aluminum alloy and has a high specific strength, specific modulus, fatigue strength, fracture toughness, and corrosion resistance stability. It has been identified as a new generation of aerospace structural material at home and abroad and has been widely studied. Due to the harsh application environment, the requirements for weld quality are particularly strict. Therefore, the weld quality and connection performance directly affect the safety and service life of the structural parts and the entire piece of equipment. In view of its important space application background, it is of great significance for the development of the space manufacturing industry to study it in depth. The friction stir welding process can be visually studied through experiments. The research mainly includes precipitation evolution and microstructure-property correlation [9]. The influence of welding parameters on the properties and microstructure of 2A14-T6 aluminum alloy joints has not been reported in many studies, but is very important from the perspective of practical application. [PERSON] [10] measured lateral force, axial force, and tool torque simultaneously by monitoring the output torque of servo motor and spindle, and checking the factors affecting welding quality. Under different combinations of tool speed and welding speed, the measurement results laid a foundation for process optimization. [PERSON] [11] studied the friction stir welding process of 2219-T6 aluminum alloy. The results showed that a void defect is formed in the joint when the rotation or welding speed is quite high. As the rotation speed or welding speed increases, the tensile strength of the joint first increases to a maximum value and then sharply decreases due to the occurrence of a void defect. [PERSON] et al. [12] focused on the microstructural and mechanical properties of the friction stir welding of AA7075-O to AA5083-O aluminum alloys. Weld microstructures, hardness, and tensile properties were evaluated in as-welded condition. Tensile tests indicated that the mechanical properties of the joint were better than in the base metals. In addition to experimental study, numerical simulation is also considered to be an important tool to study the effect of the welding process on weld quality. [PERSON] [13] studied the metallurgical and microstructure of friction stir welding (FSW) from the aspects of grain size and microhardness.