Inhomogeneous microstructure and mechanical properties of rotary friction welded AA2024 joints

The phenomenon of inhomogeneous microstructure evolution and mechanical propertiesof rotary friction welded (RFWed) AA2024 joints was investigated. The inhomogeneity wasexplored by examining the mechanical properties of samples sliced from the joint intofour parts along the radius (R): Center, 0.25R, 0.5R, 0.75R. The maximum tensile strengthof 433 MPa and elongation of 9.25% were obtained in 0.25R position. Thermo-mechanicallyaffected zone (TMAZ) was divided into two regions: Zone with distorted grains (TMAZ-I)and zone with broken grains (TMAZ-II). The softened zone on rotary side was much nar-rower than that on stationary side, which was more likely to result in the fracture in TMAZ-Ion rotary side. Dynamic recrystallized zone (DRZ) exhibited the maximum recrystalliza-tion fraction and the highest hardness but the worst plasticity. TMAZ-I mainly experiencedthe recovery which extremely enhanced the plasticity but deteriorated the hardness andstrength, moreover the width of TMAZ-I gradually increased from Center to 0.75R position.The mechanical properties of TMAZ-II fell in between DRZ and TMAZ-I owing to recoveryand recrystallization. Furthermore, the existence of TMAZ-II improved the tensile strengthin 0.25R position, while the increment of the width of TMAZ-I deteriorated the strength in0.5R and 0.75R positions. The uneven distribution of DRZ, TMAZ-I and TMAZ-II resulted inthe inhomogeneity of AA2024 aluminum alloy RFWed joints.