Long-term thermal stability of Equal Channel Angular Pressed 2024 aluminum alloy

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2016-11, Vol.677, p.307-315
• Main Authors: Tan, Güher, Kalay, Y. Eren, Gür, C. Hakan
• Format: Article
• Language: English
• Subjects: 2024 Aluminum alloy; Aluminum alloys; Aluminum base alloys; Annealing; Coarsening; Deformation mechanisms; Dislocations; Double-precipitation; ECAP; Electron microscopy; Equal channel angular pressing; Hardenability; Hardening rate; Hardness; Homology; Mechanical properties; Microhardness; Microstructure; Omega precipitate; Plastic deformation; Precipitates; Precipitation hardening; Secondary hardening; Softening; Thermal stability; Transmission electron microscopy
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2016.09.048

The strength of bulk metallic materials can be improved by creating ultra-fine grained structure via severe plastic deformation (SPD). However, the thermal stability of severely deformed materials has been a major issue that restricts their practical use within the industry. Although there are studies on the thermal stability of SPD metals, the long-term annealing response of particularly complex alloys, such as the age hardenable ones, remains undetermined. In the present study, annealing behavior of the single-pass Equal Channel Angular Pressed age hardenable 2024 Al alloy was investigated in the 0.38–0.52 homologous temperature range for up to 1000h. Microstructures and the corresponding mechanical properties of the samples were determined by transmission electron microscopy, electron back-scatter diffraction analyses, and micro-hardness measurements. After long annealing durations at 80°C and 120°C, a secondary hardening was observed whereas a fast softening occurred at 200°C. At 150°C, however, a softening followed by a slight secondary hardening was also detected. The increased coarsening rate of S precipitates accompanied with dislocation annihilation was found to be the major cause of the hardness loss. Furthermore, dislocation-rich structure and Mg clusters remaining from the S precipitate dissolution eased the nucleation of Ω precipitates which are responsible for the secondary hardening. It was concluded that below 120°C the single pass ECAPed Al 2024 components preserve their improved hardness for a prolonged period of time.