Thermal stability of the lightweight 2099 Al-Cu-Li alloy: Tensile tests and microstructural investigations after overaging

Abstract

Highlights• Lightweight AA2099(Al-Cu-Li) exhibits a thermal stability comparable or even higher than other Al-Cu alloys specifically developed for high temperature applications.• Overaged AA2099 showed high residual hardness and tensile strength, suggesting its potential use in high temperature (yet lighter) automotive components.• STEM investigations revealed the superior thermal stability of the T1 phase (typical of AlCu-Li alloys) compared to ϑ and S. AbstractThe thermal stability of the lightweight, T83 heat treated 2099 Al-Cu-Li alloy was assessed in the temperature range 200-305°C, through both hardness and tensile tests. After prolonged overaging, the alloy exhibited a better performance compared to aluminium alloys specifically developed for high temperature applications, with the advantage of a considerable lower density. The tensile behaviour was modelled through Hollomon's equation as a function of residual hardness. The changes in the alloy performance were explained through both SEM and STEM investigations. 2Microstructural analyses gave evidence of Ostwald ripening, while fractographic analyses revealed a transition from an intergranular to a ductile fracture mechanism in the overaged alloy. STEM investigations highlighted the superior thermal stability of the T1 phase compared to ϑ and S strengthening phases, which dissolved during overaging at 245°C. The study underlines the need to enhance the formation of T1 precipitates when high temperature strength is required. The results of the present study suggest that the 2099 alloy is a very promising candidate for automotive engine components, which are extremely demanding in terms of both thermal resistance and lightweight. Graphical abstract KeywordsAl-Cu-Li alloy; Thermal effect; Hardness test; Tensile test; Microstructure; STEM.

Improved Recrystallization Resistance of Al–Cu–Li–Zr Alloy through Ce Addition

“…addition of Ce and Zr in present alloy also achieves uniform dispersion coverage. In contrast to the rod-like shaped Al20Cu2Mn3 dispersoids [32], the spherical Al8Cu4Ce dispersoids (with much lower aspect ratio) formed in the Al3Zr dispersoid-free bands by joint addition of Zr and Ce, can effectively to control texture, to pin grain and sub-grain migration and to inhibit recrystallization, enhancing fracture toughness at present work [13]. For Al alloy the γ GB is 0.32 J/m 2 .…”

“…Similar with Mn and Zr which have the opposite microsegregation patterns in Al alloy [18], the joint addition of Ce and Zr in present alloy also achieves uniform dispersion coverage. In contrast to the rod-like shaped Al 20 Cu 2 Mn 3 dispersoids [32], the spherical Al 8 Cu 4 Ce dispersoids (with much lower aspect ratio) formed in the Al 3 Zr dispersoid-free bands by joint addition of Zr and Ce, can effectively to control texture, to pin grain and sub-grain migration and to inhibit recrystallization, enhancing fracture toughness at present work [13]. Figure 11 shows that the tensile strength and yield strength of the Ce-containing alloy were higher than those of the Ce-free alloy, by 21 and 38 MPa, respectively, after solid-solution and aging treatment.…”

“…Normally the low solute supersaturation near dendrite boundaries results in the dispersoid-free zones formed in Zr containing alloy, leading to dispersoid banding in rolled plates and a low pinning pressure in the critical region of grain boundaries where recrystallization easily initiates [11]. Similar to the opposite micro segregation patterns of Mn and Zr in Al, the joint addition of Ce and Zr is thought to produce more uniform dispersion coverage [13]. The precipitation of Ce-containing phase along dendrite boundaries easily occur and it is hardly dissolved in solid solution, due to its micro segregation patterns [14,15], and the poor solid solubility of Ce in Al alloy (only 0.05 wt % at 650 • C) [16].…”

Uneven Precipitation Behavior during the Solutionizing Course of Al‐Cu‐Mn Alloys and Their Contribution to High Temperature Strength

“…But usually, these particles formed during aging possess simple structure, and the diffusion coefficient of the constituents is high, such as Cu, Si, and Mg in the Al solution, and thus, these particles will be coarsened quickly even redissolved when they undergo another thermal history [24][25][26][27]. So, the particles of the Al-Cu-Mn phases and metastable θ phase precipitated during the solutionizing and aging courses, respectively, remarkably increase the YS and UTS at room temperature (Figure 10(a) and Table 2).…”

Effect of Transition Metals on Thermal Stability and Mechanical Properties of Aluminum

“…The subject of inter related terms grain growth and thermal stability of nanostructured aluminum alloys has accelerated many researchers to expand their area of significant work on this particular area. Several studies have been performed on Manuscript thermal stability of nanostructured aluminum alloys [4]- [6]. Generally, kinetic stabilization mechanism and thermodynamic stabilization mechanism are two basic mechanisms to control the grain growth at higher temperatures.…”