Abstract
The aim of this work was to investigate the effect of hot deformation on the aging behavior of precipitation-hardenable aluminum alloy AA7075 within a novel thermo-mechanical forming process, in order to gain insight into its precipitation kinetics. For this purpose, the material was formed at 420 °C after undergoing solution treatment to different strain levels ranging from 2% to 10% to obtain different dislocation densities. After undergoing hot deformation, aging at 120 °C with different parameters was carried out to improve the material hardness. The resulting material properties and microstructure evolution were characterized afterward using hardness measurements and a transmission electron microscope (TEM). TEM investigations revealed the formation of very fine particles for the material formed at 2%, as well as at 10%, of formed material, which act as effective barriers to dislocation motion. It was found that the response of artificial aging on the deformation degree in hot forming was less than expected due to the thermally activated mechanisms, leading to a decrease in dislocation density. Therefore, a dramatic increase in material hardness with the increase in hot deformation was not observed.
Highlights
Despite their limited cold formability, precipitation-hardenable aluminum alloys represent a high potential for application to modern automotive and aerospace industries, due to their excellent strength-to-weight ratios and their fatigue and cryogenic toughness properties [1,2]
After reaching the peak stress, solutionizing, the heated blanks were formed and quenched within the cooled forming tools the tensile curve decreased steadily and an increased true strain to failure was observed to create the supersaturated solid solution at room temperature (Table 2). After compared to those at room temperature reported in the literature for AA7075 [36]
After reaching the peak stress, the tensile curve decreased steadily and an increased true strain to failure was observed compared to those at room temperature reported in the literature for AA7075 [36]
Summary
Despite their limited cold formability, precipitation-hardenable aluminum alloys represent a high potential for application to modern automotive and aerospace industries, due to their excellent strength-to-weight ratios and their fatigue and cryogenic toughness properties [1,2]. For this reason, different forming processes at room and elevated temperatures have been proposed to overcome this limitation of high-strength aluminum alloys [3,4,5,6]. One of the promising techniques that allows the realization of complex-shaped structures was first proposed by Lin et al [7] This forming process combines hot forming and quenching of the heated sheet material after solution heat treatment using cooled forming tools. The integrated cooling during the forming operation enables high cooling rates and the creation of a supersaturated solid solution (SSSS) after solutionizing, which is needed to generate precipitate nucleation during aging treatment in the case of precipitation-hardenable aluminum alloys [12,13,14,15]
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