Research Of Mechanical Properties Of Friction Stir Welding For 2XXX/7XXX Aluminum Alloys

Friction Stir Welding (FSW) as a new solid phase welding technology is concerned widely because of its lower energy consumption, higher efficiency, low residual stress and good mechanical properties. FSW technology has been used in aviation and automobile industry. Though some studies have been done by researchers, there is still a lot of work needed to be done for FSW’s application because FSW is affected by some parameters, such as rotating speed of stir pin, welding speed, reduction, inclination and thickness etc.In this thesis, the welding parameters have been chosen base on the studies of FSW technology, parameters choosing and research situation, and the FSW of AA2024-T4/AA2024-T4, AA7050-T7451/ AA7050-T7451and AA2024-T4/AA7050-T7451 have beendone at the given welding parameters. The residual stress, microstructures and micro-hardness of three different FSW joints have been investigated. The mechanical properties of three FSW joints have been gotten by tensile testing at room temperature atmosphere and at corrosion environment soaked in 3.5% NaCl liquor for 50 hours, respectively. The fracture mechanisms have been studied by fracture surface analysis. The research results show that good mechanical properties have been got at given welding parameters, the tensile strengths of FSW joints of AA2024-T4/AA2024-T4 and AA7050-T7451/ AA7050-T7451 are 90.2% and 91.6% of that of base alloys respectively, while AA2024-T4/AA7050-T7451 is 90.2% of that of AA2024-T4 at room temperature atmosphere. All three FSW joints show good microstructures. The distributions of residual stress appear‘M’type, while the distribution of micro-hardness appear‘W’model, the maximum value of micro-hardness is generally at the nugget zone of the FSW joints. Compared with the mechanical properties at room temperature atmosphere, an obvious decreasing of mechanical properties for the three FSW joints has been seen at corrosion environment. The fractures of three FSW joints are ductile fracture, and the fractures occur at the region between TMAZ and HAZ in the advancing side of joints.The research results of this paper give ideal welding parameters for FSW of AA2024-T4/AA2024-T4, AA7050-T7451/AA7050-T7451 and AA2024-T4/AA7050-T7451. At the same time, the results of mechanical properties in this paper are important for the structural design of the three FSW components.