Effect of Heat Input on Microstructure and Mechanical Properties of Friction Stir Welded AA2024 and AA7075 Dissimilar Alloys

In this study, the heat input from friction stir welding of AA2024 and AA7075 dissimilar alloys was calculated, and the relationship between the heat input and mechanical properties was studied in detail. Additionally, the effect of heat on welding was analyzed. When the welding parameters were 800 rpm-400 mm/min, the Ultimate tensile strength of the joint was at its highest (346 MPa), and the elongation was 3%. A significantly higher or lower temperature led to lower tensile strength and elongation. Too low heat input failed to deform the material completely, and the fluidity of the material formed from the two base metals was poor. Excessive heat input led to the dissolution of precipitates, grain coarsening, reduced grain bonding, and other microstructural changes. When the heat input is higher, the cooling rate is faster, which can easily cause holes at the bonding interface. In the stir zone, owing to the difference in the thermal gradient of the upper and lower parts, the bottom of the material is not softened completely owing to the lack of heat, and stress concentration occurs.