.2197 Aluminum Lithium Alloy Microstructure And Properties

The relationship between microstructure evolution and properties (including mechanical properties, thermal stability and anisotropy) , and the independent and combined effects of small additions of Sc, Ag and Mg on mechanical properties and aging microstructure of 2197 alloy were studied. By tensile test and TEM observation, the conclusions can be summarized as the following:1. 2197 alloy can obtain the optimistical combination of strength and ductility in T8 temper: Solution-treated at 510℃ for 1h + water quenched + cold working to a level of 6% prior to aging at 177℃ for 20h: σ_b=474.1MPa, σ₀.2=428.2Mpa, 8 =9.2%.2. The major strengthening phase is δ ' particles in the underaged condition and a few δ' , θ' and T1 phase in the peakaged condition in T6 temper in 2197 alloy. 2197 alloy only have medium strength because the strengthening effect of Tl precipitation is much more than that of δ' . Prior deformation leads to an acceleration of aging response and enhances strength greatly because of an increased density of refined Tl precipitations in T8 temper.3. Anisotropy of the properties is attributed to the combination of crystallograthic texture and precipitation (Tl precipitation) in Al-Li alloys. Inhomogeheous distribution of Tl precipitation on the four hahit planes, {111}-, influences the anisotropy of the properties. Depressive Al₆Mn particles can make Tl precipitation more homogeneously nucleat which lower the anisotropy of the properties.4. Lower Li concentration (1.3¹.7wt%) makes 2197 alloy have better thermal stability.5. The addition of Sc doesn't change mechanical properties of 2197 alloy and thekinds of major strengthening phases, but forms . primary AI3SC particles and AlsLi/A^Sc complex phase. On the other hand, formation and accelerated coarsening of the primary AI3SC particles and AI3U/AI3SC complex phase don't improve the strength and ductility of 2197 alloy.6. Independent small addition of Ag enhances peakaging strength to a larger extent and the different aging-strengthening effect is accompanied by the different concentration of Ag. 2197 alloy has the largest solution-strengthening effect and the strongest aging response and aging-strengthening effect by the combined addition of Ag and Mg. Independent and combined roles of small addition Ag and Mg can be interpreted in terms of the solute-vacance interaction and solute-solute atom interaction. After the addition of Ag and Mg, Mg-Ag, Li-Ag, Mg-Cu clusters form rapidly because of the strong interaction between solute atoms. Thus, precipitation of Tl is significantly encouraged by the Mg-Ag co-clusters gathering on the f 111 > 0 habit planes which act as a carrier to link Al,Cu and Li atom together. Independent small addition of Ag can make Tl precipitation longer by reduce nucleating and longing energy.