Strengthening mechanisms, deformation behavior, and anisotropic mechanical properties of Al-Li alloys: A review

Aluminium-lithium alloys hold promise of providing a breakthrough response to the crying need for lightweight alloys for use as structurals in aerospace applications. Considerable worldwide research has gone into developing a range of these alloys over the last three decades. As a result, substantial understanding has been developed of the microstructure-based micromechanisms of strengthening, of fatigue and fracture as well as of anisotropy in mechanical properties. However, these alloys have not yet greatly displaced the conventionally used denser Al alloys on account of their poorer ductility, fracture toughness and low cycle fatigue resistance. This review aims to summarise the work pertaining to study of structure and mechanical properties with a view to indicate the directions that have been and can be pursued to overcome property limitations.

http://www.dunand.northwestern.edu/refs/files/Pe1062.pdf

Mechanical behaviour of aluminium-lithium alloys

A large-scale billet of 2195 Al-Cu-Li alloy was prepared by spray deposition technology. The hot extrusion, solution treatment, pre-stretching, and aging treatment were performed on the deposited billet. It was found that the yield strength, ultimate tensile strength and elongation of the T83-treated alloy reach 600 MPa, 632 MPa and 10%, respectively. The microstructures of the deposited alloy in the thermo-mechanical processing were studied by optical microscopy, scanning electron microscopy and transmission electron microscopy. The mechanical properties were examined by tensile test. It was found that the spray deposited alloy presents a microstructure with fine equiaxed grains and low segregation degree. After hot extrusion, a typical fibrous structure with incomplete recrystallization is formed. After solution and aging treatments, lots of T1 and δ ′ phases precipitate in the matrix, leading to significant increase of the tensile strength. Pre-stretch prior to aging treatment produces a fine homogeneous distribution of the T1 plates throughout the matrix, which lead to an excellent tensile performance. The ductility of aged alloys is affected by the microstructure of grain boundary. Narrow precipitate free zone and dispersed grain boundary precipitates with small size are beneficial to improvement of alloy's ductility.

Microstructures and mechanical properties of spray deposited 2195 Al-Cu-Li alloy through thermo-mechanical processing

On the AA2198-T851 alloy microstructure and its correlation with localized corrosion behaviour

Yield strength of an Al–3.7Cu–1.5Li–0.50Zn–0.37Mg–0.30Mn–0.14Zr alloy aged at 165 °C has been examined as a function of time. Phases existing in this alloy were identified by selected area electron diffraction analysis. Microstructure evolution was examined by transmission electron microscopy (TEM). The peak-ageing time determined is 50 h with yield strength of 453 MPa. Beside commonly distributed precipitates T 1 , δ ′ and θ ′, σ phase has been observed too. This is the first experimental evidence for the existence of σ in Al–Cu–Li alloys. The strength of the alloy increases rapidly during the first 24 h of ageing due to the combinative hardening effect of T 1 , θ ′, θ ″, δ ′ and σ . Additional strengthening was obtained for further ageing up to 50 h due to evolution of T 1 and θ ′ plates. Finally, coarsening led to strength decrease at prolonged ageing process.

Effect of ageing time on strength and microstructures of an Al–Cu–Li–Zn–Mg–Mn–Zr alloy

Low cycle fatigue (LCF) resistance data from binary Al–Li, ternary Al–Li–Cu, and quaternary Al–Li–Cu–Mg alloys have been compiled and discussed. The LCF resistance is measured in terms of the variation of the number of reversals to failure 2N fwith the plastic strain amplitude Δɛ p /2 as well as a modified average plastic strain energy per cycle (ΔW p )modified , obtained at different applied total strain amplitudes (Δɛ t /2). The data show the effects of microstructural features, namely dominant strengthening precipitates and the degree of recrystallisation as well as crystallographic texture. Lithium content, when in excess of 2·5 wt-%in aluminium decreases the low cycle fatigue resistance the most. The degree of aging, the degree of recrystallisation, and the degree of texture also influence the LCF resistance; among which the effect of the degree of aging is the most pronounced. The effects of lithium content in aluminium solid solution and strengthening precipitates obtainable by the change i...

P. Rama Rao

Papers

Mechanical behaviour of aluminium-lithium alloys

Low cycle fatigue resistance of Al-Li alloys