Key Takeaways & Executive Findings
- •• Hot deformation increases quench sensitivity of 7085 alloy, as evidenced by the hardness difference between water quenching and air cooling rising from 5.4% to 10.4%. • Recrystallization and subgrain structures with high dislocation density are induced by hot deformation, promoting heterogeneous precipitation during slow quenching. • High-angle grain boundaries and non-coherent Al3Zr particles serve as primary nucleation sites for η and T phases, while high-dislocation-density subgrain boundaries also facilitate nucleation. • A newly observed Y phase precipitates at dislocation sites within subgrains, providing additional insight into quench-induced precipitation mechanisms.
Abstract
The effect of hot deformation on the quench sensitivity of the 7085 alloy was studied through hardness testing and microstructure characterization. The findings indicate that hot deformation enhances the quench sensitivity of the 7085 alloy, with the hardness difference between water quenching and air cooling increasing from 5.4% (before hot deformation) to 10.4% (after hot deformation). In the undeformed samples, the Al3Zr particles within the grains exhibit better coherent with the Al matrix. During slow quenching, only the η phase is observed on Al3Zr particles and at the grain boundaries. Hot deformation leads to a mass of recrystallization and the formation of subgrains with high dislocation density. This results in an increase in the types, quantities, and sizes of heterogeneous precipitates during quenching. In the slow quenching process, high angle grain boundaries are best for the nucleation and growth of the η phase. Secondly, a substantial quantity of η and T phases precipitate on the non-coherent Al3Zr phase within the recrystallized grains. The locations with high dislocation density subgrains (boundaries) serve as nucleation positions for the η and T phases precipitating. Additionally, the Y phase is observed to precipitate at dislocation sites within the subgrains.
1. Introduction
The Al-Zn-Mg-Cu alloy exhibits high strength after undergoing processes such as solution heat treatment, quenching, and aging, making it a widely utilized structural material, particularly in the aerospace industry. With the swift development of the aerospace industry, there is a notable trend towards the integration and large-scale development of aircraft structural components. This trend imposes demands on aerospace aluminum alloys for high strength, high fracture toughness, corrosion resistance, and fatigue resistance. The uniformity and consistency of thick plates are also increasingly emphasized [1 −5]. The 7085 aluminum alloy represents a new generation of high-end aluminum alloy materials, characterized by high comprehensive performance, good quenching penetration, fatigue resistance, and damage tolerance. Hot deformation and quenching are crucial steps in the manufacturing of thick plates of the 7085 alloy. With a reduction in the quenching rate, the quantity and size of heterogeneous precipitated phases increase during the quenching process. This leads to a reduction in age-hardening phases, resulting in a decrease in mechanical performance, a phenomenon known as quench sensitivity [6, 7]. For thick plates with large cross-sectional dimensions, there is a significant reduction in cooling rate from the surface to the core during the quenching process after solution treatment. This can result in insufficient and uneven cooling rates, altering the material’s microstructure and consequently affecting its mechanical properties [8, 9].
As is well known, in the slow quenching of 7xxx series aluminum alloys, a mass of quench-induced phases are formed, and the nucleation sites of quench-induced phases, such as grain boundaries, subgrain boundaries, dislocations, and Al3Zr particles, are closely related to the grain structure [10−13]. Typically, after hot deformation treatment of 7xxx series aluminum alloys, inevitable static recrystallization occurs during the subsequent solution heat treatment process, leading to the formation of partially recrystallized and subgrain structures. During recrystallization, Al3Zr particles maintain their original orientation, while the orientation of recrystallized grains changes, causing Al3Zr particles to lose their coherency with the matrix [14]. ZHANG et al [15, 16] discovered that an increase in the hot rolling deformation of the 7050 and 7A55 alloys leads to an increase in recrystallization fraction and quench sensitivity. PAN et al [13] discovered that
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LI Cheng-bo, ZHAO Cai, CAO Pu-li, ZHU Dai-bo, XIAO Bo (2025). Effect of hot deformation on grain structure and quench sensitivity in 7085 aluminum alloy. Journal of Central South University. https://doi.org/10.1007/s11771-025-5933-3
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Frequently Asked Questions
What is quench sensitivity in aluminum alloys?
Quench sensitivity refers to the reduction in mechanical properties of age-hardenable aluminum alloys due to the formation of coarse heterogeneous precipitates during slow cooling. These precipitates deplete the alloying elements needed for age-hardening phases, thereby decreasing the final strength and hardness.
How does hot deformation affect the quench sensitivity of 7085 aluminum alloy?
Hot deformation increases the quench sensitivity of the 7085 alloy. It promotes recrystallization and the formation of subgrain structures with high dislocation density, which serve as additional nucleation sites for heterogeneous precipitates during slow quenching, leading to a greater loss in age-hardening potential.
What are the primary nucleation sites for quench-induced phases in 7085 alloy?
The primary nucleation sites are high-angle grain boundaries, non-coherent Al3Zr particles within recrystallized grains, and high-dislocation-density subgrain boundaries. These features are particularly effective for the nucleation and growth of η and T phases during slow cooling.
Why does the hardness difference between water quenching and air cooling increase after hot deformation?
After hot deformation, the alloy undergoes recrystallization and forms subgrains with high dislocation density. During air cooling, these features promote excessive heterogeneous precipitation, which reduces the availability of solutes for age hardening. Consequently, the hardness of air-cooled samples drops significantly, widening the gap compared to water-quenched samples from 5.4% to 10.4%.
What role do Al3Zr particles play during quenching of 7085 alloy?
In undeformed samples, Al3Zr particles are coherent with the aluminum matrix and are relatively weak nucleation sites. However, after hot deformation and recrystallization, these particles lose coherency and become potent sites for the nucleation of η and T phases during slow quenching, thereby increasing quench sensitivity.
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