Effect of T1 precipitate on the anisotropy of AlLi alloy 2090

Effect of Initial Orientation on the Anisotropy in Microstructure and Mechanical Properties of 2195 Al-Li Alloy Sheet during Hot Tensile Deformation

The 2195 Al-Li alloy, as one of the representative third-generation Al-Li alloys, has extensive applications in lightweight aerospace structures. In this paper, the anisotropy in mechanical properties and microstructure evolution of 2195 Al-Li alloy sheets were investigated under a strain rate of 0.01, 0.1, 1 s^-1 and a temperature of 440 and 500 °C. Experimental results showed that the hot tensile properties of the 2195 Al-Li alloy sheet exhibited a strong dependence on loading directions. The peak stress (PS) and elongation (EL) along the rolling direction (RD) were larger than the transverse direction (TD). For the tests carried out at 440 °C-1 s^-1, the PS values of the sheets stretched along the RD and TD are 142.9 MPa and 110.2 MPa, respectively. And, most of the PS anisotropy values are larger than 15%. The anisotropy in EL is less significant than in PS. All the differences are about 10%. Moreover, dimples in the samples stretched along RD were more and deeper than those along TD at 440 °C. The fracture morphology along RD and TD were similar, and both were cleavage fractures at 500 °C. Particularly, the fractions of high angle grain boundaries (HAGBs) along TD were all about 5% larger than those of RD. And, there were more small-sized continuous dynamic recrystallization (CDRX) grains inside the initial grains and discontinuous dynamic recrystallization (DDRX) grains featured with the local bulge of grain boundaries along TD. This was due to the smaller average Schmid factor and the vertical EL trend of the initial grains when the samples were stretched along TD. A model of grain evolution during the dynamic recrystallization (DRX) along RD and TD was proposed based on EBSD results. The Schmid factor and banded structure had a more prominent effect on the hot ductility of the 2195 Al-Li alloy compared with the degree of DRX, thus presenting a higher EL and better hot ductility along RD.

Erosion Layer Growth between Solid 316L Stainless Steel and Al–Li Alloy Melt

The erosion experiments of Al–Li melt on 316L stainless steel were carried out at different temperatures and holding times. In this study, the microstructure and composition of an Al–Li/316L liquid–solid interface was analyzed by inductively coupled plasma atomic emission spectroscope (ICP-AES), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The phase transformation and structure evolution of the erosion process were studied to explain the erosion mechanism and kinetics. The results showed that Fe/Cr/Ni–Al intermetallic compounds (IMC) were formed at the Al–Li/316L interface, and the diffusion of Cr atoms lead to the accumulation of Ti in the Al–Li melt, to form TiAl3 and CrAl4. With the increase in temperature and holding time, the thickness of the Fe-containing erosion layer (EL) increased, and the morphology of Ti-containing erosion particles (EP) became larger and more regular. The apparent activation energy (Ea) of the Fe-containing erosion layer was 124.82 kJ·mol−1. Meanwhile, a kinetics equation for predicting the service life of 316L was obtained. The research results provided a theoretical guidance for the smelting and casting of an Al–Li alloy.

Contribution of a new generation field-emission scanning electron microscope in the understanding of a 2099 Al-Li alloy

Aluminum-lithium alloys are widespread in the aerospace industry. The new 2099 and 2199 alloys provide improved properties, but their microstructure and texture are not well known. This article describes how state-of-the-art field-emission scanning electron microscopy (FE-SEM) can contribute to the characterization of the 2099 aluminum-lithium alloy and metallic alloys in general. Investigations were carried out on bulk and thinned samples. Backscattered electron imaging at 3 kV and scanning transmission electron microscope imaging at 30 kV along with highly efficient microanalysis permitted correlation of experimental and expected structures. Although our results confirm previous studies, this work points out possible substitutions of Mg and Zn with Li, Al, and Cu in the T1 precipitates. Zinc and magnesium are also present in "rice grain"-shaped precipitates at the grain boundaries. The versatility of the FE-SEM is highlighted as it provides information in the macro- and microscales with relevant details. Its ability to probe the distribution of precipitates from nano- to microsizes throughout the matrix makes FE-SEM an essential technique for the characterization of metallic alloys.

Crystallographic Texture and Yield Behavior of Al-Cu-Li (2195) Plate

Existing experimental texture analysis capabilities allow testing of theories on plasticity using polycrystal models. Aluminum-lithium alloys, which are particularly suited for aerospace applications due to excellent strength to weight ratio, typically possess pronounced texture. Al- Cu-Li (2195) thick plates were deformed by cold rolling to various thickness reductions. The plates exhibit a texture gradient through the plate thickness accompanied by a variation in yield strength values. The difference in yield strength values is related to the texture variation in terms of the texture components (ideal crystallographic orientations) identified from experimental measurements. A modified Taylor-based polycrystal plasticity model developed by Kocks and his colleagues is used to predict yield surfaces by incorporating texture data. Results of this investigation show that the texture intensities measured at certain ideal orientations increase or decrease with increasing deformation. These textural changes influence the value and anisotropy of the yield strength of the alloy.