Precipitates, Anisotropy Of Al-Li Alloys And Influence Of Static Electric Field

Based on the study of 1420 Al-Li alloy strengthened by a single precipitate, the author study strengthening contributions and their anisotropies of each phase and that of deformed textures to anisotropy in 2090 and 2090+Ce alloys strengthened by two precipitates, by reversion treatment and the exponential additional rule. It shows that while crystal textures formed during deforming process have basal contribution to anisotropy of alloys, precipitates also have important contribution to anisotropy of alloys and they decide changes of anisotropy in aging process.Contributions of 8 and TI phases to anisotropy of alloys are analyzed quantitatively. Strengthening contributions of ' phase are maximal in the rolling and transverse directions, minimal in the 45 direction, which means that contribution of ' phase to anisotropy of alloys is consentaneous with that of textures. And strengthening contribution of T1 phase is maximal in the rolling direction, minimal in the transverse direction, and midterm in the 45 direction, which means that contribution of T1 phase to anisotropy of alloys is contrary to that of textures. It is found that ' phase produces coplanar slip and reduces the number of movable slip systems because its particles are cut by moving dislocations in deforming process, for its large critical size of cut-bypass, accordingly its strengthening contribution is anisotropic. And strengthening contribution of T1 phase is also anisotropic because it distributes on the four {111} slip planes while its critical size is small.Addition of minim cerium to the Al-Li alloy enhances textures of alloys, thereby increases anisotropy of the alloy, on the other hand it influences anisotropy of the alloy by its effect on aging process. In early stage of aging, cerium lessens influence of coplanar slip on anisotropy by making ' phase particles smaller and more disperse, while it makes contribution of T1 phase to anisotropy contrary to that of textures. Further more, cerium stays aging process to some extent in 2090 alloy.Influences of electric field applying during solution process on mechanical properties, fracture characters and precipitates in aged alloys are studied. It is found that the electric, field improves elongations in 2090 and 2090+Ce alloys markedly, especially in 2090 alloy, but has little effect on strengths. At the same time, the electric field lessenes percentages of intergranular delamination and increases transgranular fracture and microscopic plastic deformation. Besides, the electric field makes both average particle size and its distributing range of 8 ' phase smaller, and reduces the halfwidth of PFZ in aged alloys.Kinetics of 8' phase precipitation and influence of electric field applying during solution process are studied by differential scanning calorimetry (DSC) technique. Caculation is carried through adopting mechanism function of the first order reaction, F1: f( )=l - . The results have good linear relativities, a, the precipitated fractions are excellently representative, and F1 is ascertained the most probably mechanism function of ' phase precipitation. The electric field reduces activation energies of ' phase precipitation and average sizes of ' particles both in 2090 and 1420 alloys. Caculation results accord well with those of TEM experiments.Influences of electric field applying during aging process on mechanical properties, fracture characters and precipitate in 1420 alloy are studied. It is found that the electric field improves elongations in 1420 alloy markedly, but has little effect on strengths. At the same time, the electric field lessenes percentages of intergranular delamination and increases transgranular fracture and microscopic plastic deformation. Besides, the electric field increses both average particle size and of 8' phase and the half width of PFZ.Kinetics of 8' phase dissolution in aged 1420 alloy and influence of electric field applying during aging process are studied by DSC technique. Caculation is carried through adopting mechan...