Browsing by Author "Shojaei, Kambiz"

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Ambient and elevated temperature mechanical behavior of a high strength aluminum alloy after cold deformation
(2016-01) Shojaei, Kambiz; Yapıcı, Güney Güven; Yapıcı, Güney Güven; Atlı, K. C.; Bundur, Zeynep Başaran; Department of Mechanical Engineering; Shojaei, Kambiz
Nowadays, aluminum alloys in automotive and aerospace industries have assigned a noticeable portion in structural applications in comparison to many steel alloys. The aim of this study was to investigate the high-temperature deformation behavior and microstructural evolution of Al-Zn-Mg-Cu aluminum alloy for two different annealed and cold rolled conditions. The elevated temperature deformation behavior and microstructural evolution of 7075 aluminum alloy at the annealed and cold rolled conditions have been studied. Isothermal uniaxial tensile tests at different temperatures of ambient temperature, 200, 250, 300 and 350 C and strain rates of 0.001, 0.01, 0.1 s−1 were conducted. The effects of two important factors; deformation temperature and strain rate sensitivity on the tensile deformation behaviors with support of fracture mechanism characteristics are discussed in details. The Zener-Hollomon parameter in an exponenttype equation has been utilized for both tested conditions in order to calculate the activation energy for the studied conditions. The results review indicates that with the increase of deformation temperature or the decrease of strain rate, the fraction of recrystallized grains increases which leads to higher elongation. This is mainly attributed to dynamic recrystallization during the tensile deformation. Accordingly, the maximum UTS value at elevated deformation temperature has been reported 218 MPa in rolled samples at 200 C under the strain rate of 0.1 s−1, whereas the maximum elongation to fracture was 55.9% in rolled samples at 350 C under the strain rate of 0.01 s−1. In addition, unlike annealed condition it has been observed that the cold working has a remarkable effect on increasing the peak stress and also leads to higher ductility at elevated deformation temperatures. But in contrast, at ambient temperature it has been observed that severely cold work could decrease the ductility. However, at 350 C and 0.001 s−1 the general trend of softening has changed and the ductility dropped which could be imputed to the dynamic precipitation resulting in the formation of the secondary phases during high-temperature deformation. Observation of the fracture surfaces in the studied deformation conditions has showed that localized necking caused the final fracture of the specimens in which microvoids can be seen at lower deformation temperatures. Whereas by increasing the deformation temperature coalescence of dimples and micro voids leading to a relatively coarse but less dense morphology resulted in fracture.