Influence of Hot Deformation on the Precipitation Hardening of High-Strength Aluminum AA7075 during Thermo-Mechanical Processing

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.

Hot Sheet Metal Forming Strategies for High‐Strength Aluminum Alloys: A Review—Fundamentals and Applications

“…In another study, [ 178 ] therefore, to emulate an integrated hot stamping process and to determine the influence of defined degrees of deformation on the distribution of final material hardness distribution, hot deformation ranging from 2% to 10% was conducted at 420 °C within a tensile testing machine equipped with a moveable inductor and contact cooling devices after solution heat treatment and prior to artificial aging. The results were then compared to the distribution of the same properties, after artificial aging, of a part formed under industrial conditions using the same process parameters.…”

Flow Behavior and Mechanical Properties of Multi-Pass Thermomechanically Processed 7075 Al-Alloy

“…Due to the rapid pace of technological advancement, many academics and manufacturers have been searching for sustainable ways to increase fuel use efficiency as awareness of global warming, environmental degradation, and the limitations of fossil fuel supplies has grown [1][2][3][4]. There is an unfulfilled need for novel materials with favorable strength-to-weight ratios [2,[5][6][7][8]. The 7000 series has outstanding characteristics among the many classes of Al-alloys, particularly low density, increased specific strength, and stress corrosion cracking resistance [2][3][4][7][8][9][10][11][12].…”

“…Careful control of the hot rolling processing parameters can create materials with exceptional combinations of mechanical properties [2,11]. Most related investigations have focused on analyzing the flow behavior of the alloy during hot compression and hot tension testing to determine the best hot forming conditions [1][2][3][4][5][6][7][8][9][10][11][12][13]. The 7075 Al-alloy is claimed to be highly workable over a wide temperature range and develops a complex microstructure with a reduced grain size due to the occurrence of dynamic recovery and dynamic recrystallization during thermomechanical processing, which improves its mechanical attributes [2,6].…”

“…The presence of these particles has a considerable impact on the alloy's workability at high temperatures as well as its mechanical properties at ambient temperature [2]. Therefore, to gain a deep comprehension of the microstructure and mechanical properties following processing, it is essential to understand the intricate precipitation behavior and interactions between precipitation and dislocation in highstrength Al-alloys [2,6].…”

“…Regarding the post-processing, they [11] also found that T6 heat treatment after hot rolling improved the mechanical properties due to the recrystallization and precipitation of the second phase. Scharifi et al [6] investigated the impact of thermomechanical processing on the aging kinetics and hardness of 7075 Al-alloy. They reported a weak response of hardness to aging as a result of reducing the dislocation density due to the occurrence of recovery and recrystallization mechanisms.…”