Abstract
The influence of heating rate on the microstructural evolution of a cold-rolled AA7075 alloy sheet during solution heat treatment was examined using electrical conductivity, scanning electron microscopy, X-ray diffraction, transmission electron microscopy and electron backscatter diffraction. The results indicate that the dissolution of soluble phases takes place during the heating process. The heating rates affect the dissolution process of soluble phases, and these phases completely dissolve into matrix after solution treatment. Recrystallized and elongated grains are produced after solution treatment by both fast and slow heating rates, while the grains of the rapidly heated sample are much finer. The elongated grains are attributed to the difference in the pinning pressure of boundary migration between the rolling and normal directions. The {111}<110> texture, as well as typical recrystallization textures, were found in both fast and slowly heated samples after solution treatment, but the textures, especially the {111}<110> component in the slow-heated sample, are much stronger, leading to an anisotropy in the tensile properties after artificial aging.
Highlights
Al-Zn-Mg-(Cu) alloys have been widely used in aircrafts due to their high static strength and fracture toughness [1,2,3]
The sub-grain sizes were obtained by processing the electron backscatter diffraction (EBSD) data and the results show that the sub-grain sizes of the Fast heating (FH) sample and the slow heating (SH) sample quenched at 300 ◦ C are 137.0 ± 26.8 and 246.1 ± 51.0 nm, respectively
The dissolution of the η phase during the solution treatment is controlled by the diffusion temperature and time, which are related to the heating rates
Summary
Al-Zn-Mg-(Cu) alloys have been widely used in aircrafts due to their high static strength and fracture toughness [1,2,3]. The effects of heating rate during solution treatment on microstructures and textures have been studied in Al-Cu-Mg [13] and Al-Mg-Si-Cu alloys [14]. Before solution treatment Al-Zn-Mg-(Cu) alloys contain constituents, dispersoids and equilibrium η precipitates. Equilibrium η phases may grow up to micron scale under favorable conditions; equilibrium η phases are soluble and can completely dissolve during solution treatment Both the dispersoids and precipitates have been reported to interact with dislocations [18], as well as sub-grain and grain boundaries [18,19,20,21,22] when recovery and recrystallization occur. The coexistence of constituents, dispersoids and precipitates makes the recovery and recrystallization behavior highly complex during solution treatment. The dissolution of the equilibrium precipitates, recovery, and recrystallization during the heating process of the solution treatment are discussed in detail
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