Key Takeaways & Executive Findings
- •• FSAM effectively refines grains and increases high-angle grain boundaries in 2195 Al-Li alloys, regardless of initial heat-treatment state (T3 or T8). • The heat-treatment state has minimal influence on the final microstructure after FSAM, as processing temperatures exceed the solid solution temperature. • Tensile strengths of the nugget zone reach up to 478 MPa (T3) and 481 MPa (T8) in lap experiments, demonstrating significant mechanical property improvements. • The study provides a foundation for optimizing FSAM parameters to achieve tailored microstructures and enhanced performance in aerospace-grade Al-Li alloys.
Abstract
Friction stir additive manufacturing (FSAM) is an innovative additive manufacturing (AM) method. The various heat treatment conditions of aluminum-lithium alloys using this method have not been widely discussed. In this study, the microstructure evolution and mechanical properties of FSAM 2195 aluminum-lithium alloy in different heat treatment conditions (T3 and T8) were investigated. The results demonstrated that the heat treatment state of 2195 Al-Li alloys was minimally influenced by FSAM as the FSAM temperature exceeded the solid solution temperature. After conducting a single-pass FSAM experiment, a notable grain refinement was observed in the nugget zone (NZ) region compared to the base material (BM). The average grain size of the 2195-T3 alloy decreased from 6.1 to 2.9 μm, while the proportion of high-angle grain boundaries increased from 16.5% to 43.9%. Similarly, the average grain size of the 2195-T8 alloy decreased from 8.9 to 2.8 μm, with an increase in high-angle grain boundary from 37.6% to 59.2%. The tensile strength of the 2195-T3 Al-Li alloy reached 466 and 478 MPa in the NZ of single-pass and lap experiments, respectively. In comparison, the tensile strength of the 2195-T8 Al-Li alloy in the NZ could reach 452 and 481 MPa in single-pass and lap experiments, respectively. These results demonstrate the significant improvements in microstructure and mechanical properties were achieved through the FSAM process.
1. Introduction
Aluminum-lithium alloys are extensively utilized in the aerospace industry as a fundamental structural material, recognized for their remarkable strength, outstanding low-temperature plasticity, and superior corrosion resistance [1−9]. The alloy is currently being effectively employed in a variety of critical aerospace applications. As a standard heat-treatable strengthening alloy, the 2195 Al-Li alloy typically undergoes the T8 heat treatment process. This process enhances the component's performance by subjecting it to a specific deformation following solid solution treatment, and subsequently completing the aging process [10].
DAI et al [10] conducted a low-temperature pre-rolling T8 treatment on Ag-free 2195 Al-Li alloy. Their findings revealed that during the aging process, dislocation rearrangement induced by dynamic recovery significantly accelerates the nucleation kinetics. This, in turn, activates additional diffusion pathways and enhances the interaction within the T1 substructure. Consequently, T8 treatments can readily produce an extra strengthening effect on the substructure that is largely absent in T6 treatments. XIE et al [11] and their colleagues conducted a comprehensive study on the aging process of 2195 Al-Li alloy, focusing on the effects of pre-deformation on its mechanical properties and precipitation behavior. The research findings indicate that pre-deformation plays a pivotal role in facilitating the precipitation of the AlCuLi phase, acting as nucleation sites for this phase through the process of deformation. Moreover, an increase in temperature was observed to enhance the diffusion rate of Cu atoms, thereby significantly accelerating the precipitation of the Al2Cu phase. Furthermore, the integration of two-stage aging and pre-deformation has demonstrated a dual advantage for the 2195 Al-Li alloy, enhancing both its strength and elongation concurrently. TAO et al [12] conducted an investigation into the precipitation behavior of Al-4Cu-1Li alloys at temperatures ranging from 100 to 175 ℃. The results indicated that as the aging temperature increased, the microstructure of the material evolved from GP zone and θ' phase to T1 and θ' phase. This transition led to a gra
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GAO Yong-hui, JIANG Tao, DAI Guo-qing, LI Jun, GUO Yan-hua, SUN Zhong-gang, LIU Chun-hui, ZHAN Li-hua (2025). Microstructure evolution and mechanical properties of 2195 Al-Li alloy with different heat-treatment states via friction stir additive manufacturing. Journal of Central South University. https://doi.org/10.1007/s11771-025-6084-2
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Frequently Asked Questions
What is friction stir additive manufacturing (FSAM)?
FSAM is an innovative additive manufacturing method that uses friction stir welding principles to build components layer by layer, offering advantages such as solid-state processing, fine microstructures, and improved mechanical properties.
How does FSAM affect the microstructure of 2195 Al-Li alloy?
FSAM significantly refines the grain structure in the nugget zone, reducing average grain size and increasing the proportion of high-angle grain boundaries, which enhances mechanical properties.
What are the tensile strengths achieved in this study?
In the nugget zone, the 2195-T3 alloy achieved tensile strengths of 466 MPa (single-pass) and 478 MPa (lap), while the 2195-T8 alloy achieved 452 MPa (single-pass) and 481 MPa (lap).
Does the initial heat-treatment state influence the FSAM outcome?
The study found that the heat-treatment state (T3 vs T8) has minimal influence on the final microstructure after FSAM, as the processing temperature exceeds the solid solution temperature, leading to similar refined microstructures.
What is the significance of this research for aerospace applications?
This research demonstrates that FSAM can produce 2195 Al-Li alloy components with refined microstructures and enhanced mechanical properties, which is crucial for aerospace structural applications where weight reduction and high strength are critical.
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