Key Takeaways & Executive Findings
- •• Pre-thermal treatment at 450°C for 4 h before hot rolling refines precipitate distribution, significantly reducing mechanical anisotropy in rapidly solidified 2195 alloy sheets. • The treatment promotes recrystallization during hot rolling, leading to low in-plane anisotropy factors of 1.15% for ultimate tensile strength and 0.77% for yield strength. • Subsequent peak aging at 165°C for 48 h enhances grain refinement and T1 phase uniformity while suppressing precipitation-free zones, improving strength and toughness. • The optimized process yields yield strength of 547 MPa, ultimate tensile strength of 590 MPa, and elongation of 7.7%, demonstrating potential for aerospace applications.
Abstract
The pronounced anisotropy in mechanical properties presents a major obstacle to the extensive application of aluminum-lithium (Al-Li) alloys, primarily attributed to heterogeneous precipitate distribution, grain structure variations, and crystallographic texture. This study investigates the impact of pre-thermal treatment prior to hot rolling and aging treatment on the anisotropy of mechanical properties of 2195 alloy sheet fabricated by gas atomization, hot pressing and hot rolling. The results demonstrate that pre-treatment at 450 ℃ for 4 h promotes finer and more uniform distribution of precipitates, effectively mitigating mechanical anisotropy of the alloy sheet. Additionally, this treatment facilitates recrystallization during hot rolling, further reducing mechanical anisotropy. The in-plane anisotropy (IPA) factors for ultimate tensile strength (UTS) and yield strength (YS) are 1.15% and 0.77%, respectively. Subsequent aging treatment enhances grain refinement and the uniformity of the T1 phase, suppresses the formation of precipitation-free zones (PFZs), significantly improving the strength and toughness of the alloy sheet. After peak aging at 165℃ for 48 h, the alloy sheet exhibits YS of 547 MPa, UTS of 590 MPa, and elongation (EL) of 7.7%.
1. Introduction
Aluminum-lithium (Al-Li) alloys are widely used in aerospace applications owing to their remarkable properties, such as low density, high specific strength, and superior elastic modulus. To date, Al-Li alloys have evolved through three generations. The first two generations, however, encountered substantial problems during service, including inadequate mechanical properties, processing difficulties, and pronounced mechanical anisotropy. These limitations considerably restricted the broader application of Al-Li alloys. In response, third-generation Al-Li alloys were developed by optimizing the alloy composition: reducing Li content, increasing Cu content, incorporating micro-alloying elements such as Mg, Ag, Zn, Mn, and Zr, and strictly controlling impurity elements like Fe and Si. Consequently, these alloys exhibit reduced anisotropy, enhanced thermal stability, superior strength and toughness, as well as improved formability and weldability, leading to their widespread adoption in the aerospace industry.
The 2195 alloy, a prominent third-generation Al-Li alloy, stands out for its exceptional performance and high specific strength, rendering it a favored option for aerospace applications such as the ultra-lightweight external fuel tanks of the space shuttle. Its superiority is further emphasized by the refined grain structure obtained via rapid solidification, which ensures microstructural uniformity. Compared with traditional cast alloys, the rapidly solidified 2195 alloy demonstrates superior mechanical and physical properties. Despite extensive research on the 2195 alloy, previous studies have primarily focused on manufacturing processes such as spray forming, extrusion, and heat treatment, with limited emphasis on optimizing the performance of rapidly solidified alloy sheets. This gap in research highlights the need for further investigation into improving the mechanical properties and reducing anisotropy in rapidly solidified 2195 alloy sheets.
High anisotropy can give rise to defects such as uneven deformation, thereby adversely affecting the performance and quality of manufactured alloys. Mechanical anisotropy is affected by several factors, such as crystallographic texture, grain morphology, and precipitate distribution. Among these factors, the preferred orientation of grains in polycrystalline alloys plays a major role. However, in Al alloys with an isotropic face-centered cubic (FCC) structure, texture-induced anisotropy is generally limited. Notably, Al-Li alloys, despite having the same FCC structure, exhibit pronounced anisotropic tensile properties after plastic deformation. It is well-established that S, Copper, and Brass textures are commonly observed in thermally deformed Al and Al-Li alloys. However, Al-Li alloys display a significantly higher proportion of Brass textures relative to other textures, which contributes to their anisotropic behavior.
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PENG Xiang, LI Xin-xing, WANG Ri-chu, FENG Yan, YAN Shuai-jiang, CAI Zhi-yong (2025). Anisotropy of rapidly solidified 2195 alloy rolled sheets: Effect of pre-thermal treatment prior to rolling and aging treatment. Journal of Central South University. https://doi.org/10.1007/s11771-025-5979-2
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Frequently Asked Questions
What is the main objective of this study on 2195 alloy?
The study aims to investigate the effect of pre-thermal treatment prior to hot rolling and subsequent aging treatment on the mechanical anisotropy of rapidly solidified 2195 alloy sheets, with the goal of reducing anisotropy and improving overall mechanical properties.
What specific pre-thermal treatment condition was found to be effective?
Pre-treatment at 450 °C for 4 h was found to promote finer and more uniform distribution of precipitates, effectively mitigating mechanical anisotropy and facilitating recrystallization during hot rolling.
How much was the in-plane anisotropy reduced by the optimized process?
The in-plane anisotropy (IPA) factors for ultimate tensile strength (UTS) and yield strength (YS) were reduced to 1.15% and 0.77%, respectively, after the optimized pre-thermal treatment and rolling.
What mechanical properties were achieved after peak aging?
After peak aging at 165°C for 48 h, the alloy sheet exhibited a yield strength of 547 MPa, ultimate tensile strength of 590 MPa, and elongation of 7.7%.
Why is reducing anisotropy important for Al-Li alloys in aerospace applications?
High anisotropy can lead to uneven deformation and degraded performance. Reducing anisotropy ensures more uniform mechanical properties, which is critical for structural components in aerospace applications where reliability and consistency are essential.
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