Inhomogeneous microstructure and mechanical properties of rotary friction welded AA2024 joints

The phenomenon of inhomogeneous microstructure evolution and mechanical properties of rotary friction welded (RFWed) AA2024 joints was investigated. The inhomogeneity was explored by examining the mechanical properties of samples sliced from the joint into four parts along the radius (R): Center, 0.25R, 0.5R, 0.75R. The maximum tensile strength of 433 MPa and elongation of 9.25% were obtained in 0.25R position. Thermo-mechanically affected 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 narrower than that on stationary side, which was more likely to result in the fracture in TMAZ-I on rotary side. Dynamic recrystallized zone (DRZ) exhibited the maximum recrystallization fraction and the highest hardness but the worst plasticity. TMAZ-I mainly experienced the recovery which extremely enhanced the plasticity but deteriorated the hardness and strength, 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 recovery and recrystallization. Furthermore, the existence of TMAZ-II improved the tensile strength in 0.25R position, while the increment of the width of TMAZ-I deteriorated the strength in 0.5R and 0.75R positions. The uneven distribution of DRZ, TMAZ-I and TMAZ-II resulted in the inhomogeneity of AA2024 aluminum alloy RFWed joints. (C) 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).