Key Takeaways & Executive Findings
- •• ECAP combined with inter-pass aging promotes bimodal η′ precipitates and high dislocation densities in AA7050. • Grain size refines to 4.8 μm and dislocation density increases to 1.24×10^15 m−2 via precipitate pinning. • Precipitation, fine-grain, and dislocation strengthening synergistically yield UTS ~610 MPa and YS ~565 MPa. • Ductility is maintained through coordinated grain boundary sliding and uniform, fine second-phase dispersion.
Abstract
In this study, the interaction between deformation and precipitates during multiple equal channel angular pressing (ECAP) deformations and inter-pass aging combination and its effect on the mechanical properties of 7050 aluminum alloy are studied. The result show that ECAP induces numerous substructures and dislocations, effectively promoting the precipitation of the ηʹ phase exhibiting a bimodal structure during inter-pass aging. Following inter-pass aging and subsequent ECAP, the decrease in grain size (4.8 μm) is together with the increase in dislocation density (1.24×1015 m−2) due to the pinning effect of the precipitated phase. Simultaneously, the dislocation motion causes the second phase particles to become even finer and more diffuse. The synergistic effects of precipitation strengthening, fine grain strengthening, and dislocation strengthening collectively enhance the high strength of aluminum alloys, with ultimate tensile strength and yield strength reaching approximately 610 and 565 MPa, respectively. Meanwhile, ductility remains largely unchanged, primarily due to coordinated grain boundary sliding and the uniform and fine dispersion of second phase particles.
1. Introduction
Al-Zn-Mg-Cu (7xxx) alloy has great appeal in the fields of transportation, military equipment, and aerospace due to its lightweight, high specific strength, and easy formability [1 −4]. However, considering the limitations of relatively low mechanical strength and difficulty in balancing strength and ductility, the further application of 7xxx Al alloy under some high load conditions is still limited [5, 6]. Therefore, improving the strength of alloys and achieving a balance between strength and ductility are of great significance. Heat treatment and severe plastic deformation (SPD) processes have become important means of strengthening and balancing the strength and ductility of Al-Zn-Mg-Cu alloys [7−9].
Among SPD techniques, equal channel angular pressing (ECAP) is notable for its ability to produce fully dense block samples without changing the material’s cross-sectional area [10 −14]. By applying shear forces that approximate pure shear deformation to refine grains and accumulate dislocations, the strength of the alloy by using ECAP can be improved [15, 16]. However, the ductility of Al alloys after ECAP often tends to decreased significantly [17, 18].
As a representative example of heat treatable strengthening, the Al-Zn-Mg-Cu alloy can achieve high strength through the precipitation of precipitates. To achieve high strength while maintaining ductility, researchers have investigated the relationship between ECAP and aging treatments, as well as studied the impact of microstructure evolution on alloy strength and ductility [19, 20]. Among them, the effect of combining sequences on microstructure evolution and properties of alloys has especially received extensive attention in recent years [20−26].
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Li Jian, He Tao, Du Xiang-yang, Jia Dong-sheng, Vereschaka Alexy (2025). Mechanical properties and microstructure of as-cast AA7050 processed by equal channel angular pressing combined with inter-pass aging treatment. Journal of Central South University. https://doi.org/10.1007/s11771-025-5911-9
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Frequently Asked Questions
What is the purpose of combining ECAP with inter-pass aging for AA7050 alloy?
The combination aims to improve the strength of as-cast AA7050 while maintaining ductility by leveraging precipitation, fine-grain, and dislocation strengthening mechanisms.
How does inter-pass aging affect the precipitate structure?
Inter-pass aging after ECAP promotes the precipitation of η′ phase with a bimodal structure, and subsequent ECAP refines the particles further, enhancing the precipitation strengthening effect.
What are the reported mechanical properties after the combined process?
The ultimate tensile strength and yield strength reach approximately 610 MPa and 565 MPa, respectively, while ductility remains largely unchanged.
Why does ductility remain largely unchanged despite increased strength?
Ductility is preserved due to coordinated grain boundary sliding and the uniform, fine dispersion of second phase particles.
What is the role of dislocations in the process?
ECAP generates high-density dislocations that promote precipitation and, together with the pinning effect of precipitates, increase the dislocation density to 1.24×10^15 m−2, contributing to dislocation strengthening.
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