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Abstract The microstructures and mechanical properties of cast and extruded Al-4Cu-1Li-0.4Mg-0.1Zr- x Zn alloys were investigated and the amount of Zn additions was up to 1.1 wt%. The results showed that Zn addition could bring additional MgZn 2 phases at the grain boundary and slightly refine the grain size in the as-cast alloy. The mechanical properties of extruded Al-4Cu-1Li-0.4Mg-0.1Zr -x Zn alloy increased gradually with the Zn content under different conditions. The yield strength (YS) and ultimate tensile strength (UTS) of T8 treated (stretched by 4% and aged at 150 °C for 32 h) 1.1 Zn alloy could reach 639 MPa and 666 MPa, while elongation (EL) remained at 10.9%. For alloys peak-aged at 175 °C for 32 h (T6 treated), Zn could effectively promote the precipitation of T 1 phases (Al 2 CuLi) but decrease the volume fraction of θ′ phases (Al 2 Cu) in the matrix. The coarsening of T 1 phases could be obviously suppressed by the addition of Zn under overaged condition. However, the precipitate of T 1 phases promoted by Zn under the T8 condition is not as obvious as the T6 condition. [ABSTRACT FROM AUTHOR]

In this paper, mechanical properties and microstructures of the cast and extruded Al- x Cu-1Li-0.4Mg–1Zn-0.1Zr alloys (x = 2.0, 3.0, 4.0, 4.5, 5.5, 6.5 wt%) were investigated. The results showed that the as-cast micrographs of alloys with different Cu content primarily consist of dendritic α-Al grains, and the intermetallic phases at the grain boundaries were Cu and Zr rich phases. After solution treatment, no recrystallization took place in extruded alloys, and the alloys mainly represented mixed textures composed of <111> and <100> fibers. Cu significantly affected the precipitation behavior of the extruded alloys. Only T 1 (Al 2 CuLi) phases were observed in T6 (aging at 175 °C for 32 h) and T8 (3% pre-strain followed by aging at 150 °C for 32 h) treated alloy with 2 wt% Cu. Further increasing Cu contents (4.5 and 6.5 wt%) enabled the co-precipitation of T 1 and θ' (Al 2 Cu) phases, as well as increased their density. In addition, the microstructures of grain boundaries of alloys with different Cu content showed dramatic differences. T 1 phases precipitated at the grain boundaries of alloy containing 2 wt% Cu, while rare precipitation of T 1 phases was observed at the grain boundaries of alloy with 6.5 wt% Cu. The yield strength (YS) of the alloys increased with the Cu content and the elongation (EL) showed an opposite trend. A good combination of ultra-high strength (YS = 684 MPa, ultimate tensile strength = 726 MPa) and ductility (EL = 6.3%) was obtained in T8 treated alloy containing 4.5 wt% Cu. The presence of the undesired coarse T 2 (Al 6 CuLi 3) phases at the grain boundaries resulted in the premature failure of the high Cu content alloys. [ABSTRACT FROM AUTHOR]

In this work, a novel Al-4.7Cu–1Li-0.5Mg-0.1Zr–1Zn alloy was designed with the purpose of developing ultra-high strength and low-cost Al–Cu–Li alloy. The mechanical properties and microstructure evolution of the studied alloy under T6, T8, and two-stage aged conditions were investigated. The alloy showed a non-recrystallization feature during solution treatment. A strong <111> fiber texture was presented in the as-quenched alloy. The yield strength (YS), ultimate tensile strength (UTS), and elongation (EL) of the alloy was largely depended on the aging process parameters. A good combination of ultra-high strength (YS = 731 MPa, UTS = 753 MPa) and ductility (EL = 5.5%) were obtained in the T8 treated specimen (pre-stretched by 3% and aged at 150 °C for 32 h). The pre-strain prior to artificial aging and aging temperature significantly affect the distribution, density, and size of precipitates. Strengthening mechanism of the alloy was discussed in detail. The strong <111> texture preserved in the as-quenched alloy and the finely dispersed T 1 (Al 2 CuLi) phases distributed in the T8 treated specimens could account for the ultra-high strength of the present alloy. Image 1 • Zn is a candidate for Ag to develop cost-effective high strength Al–Cu–Li alloys. • A novel ultra-high strength Al-4.7Cu–1Li-0.5Mg-0.1Zr–1Zn alloy was designed. • The mechanical properties and microstructure of the alloy under different aging conditions were systematically investigated. • A high density of fine T 1 phases was distributed in the T8 treated alloy. • The introduction of pre-strain and improving the aging temperature could promote the precipitation of S' phases. [ABSTRACT FROM AUTHOR]

In this work, the influence of Sc content on the microstructure and mechanical properties of cast Al-2Li-2Cu-0.5Mg-0.2Zr alloy was investigated. It was found that the grain size of As-cast alloy was significantly reduced in steps with the increase of Sc addition, accompanied by the arising and increasing of cubic primary Al 3 (Sc, Zr) phases. No evidence for the presence of the ternary W (Al 8−x Cu 4+x Sc) phase was obtained. The volume fraction of nanoscale Al 3 (Sc, Zr) dispersoids was improved with the increase of Sc content, and the presence of Sc was observed to refine the S′ (Al 2 CuMg) morphology during ageing. The addition of Sc lowered the growth rates of δ′ (Al 3 Li) particles and δ′-Precipitate-free zones (δ′-PFZs) of the base alloy. The tensile property results showed that, with the increasing Sc content and ageing times, the yield strength (YS) and ultimate tensile strength (UTS) were continuously increased, and the highest elongation of 6.0% was obtained in the 0.2Sc-containing alloy aged for 32 h at 175 °C. The results indicated that the optimal Sc addition in cast Al-2Li-2Cu-0.5Mg-0.2Zr alloy was 0.2 wt%. [ABSTRACT FROM AUTHOR]

The microstructure, electrical conductivity and mechanical properties of cast Al-2Li-2Cu-0.5Mg-0.2Zr alloy during heat treatment were investigated. The results indicated that a population of secondary phases enriched along grain boundaries in as-cast studied alloy, most of which dissolved into the α-Al matrix after solution treatment. Profound enhancement in mechanical properties of the studied alloy was obtained after T6 heat treatment. TEM observations revealed competitive precipitation of T 1 (Al 2 CuLi) and S′ (Al 2 CuMg) phases during ageing, while no θ′ (Al 2 Cu) phase was observed. The anomalous decrease in conductivity observed during ageing was attributed to the precipitation of T 1 phases. Fine δ′ (Al 3 Li) particles were homogeneously distributed after quenching, gradual coarsening of which was observed with prolonged ageing time. As ageing proceeded, the δ′ coarsened and δ′-Precipitate-Free Zones (PFZs) developed, resulting in diminishing ductility observed from as-quenched to peak-aged state. Precipitation and continuous coarsening of T 1 phases kept on at the expense of gradual δ′ dissolution. The improvements of ductility observed in over-aged samples arose mainly from the presence of T 1 , S′ phases, Al 3 (Li,Zr) composite precipitates and progressive δ′ dissolution. Moreover, continuous coarsening of T 1 and S′ phases contributed primarily to the strength loss in over-aged studied alloy. [ABSTRACT FROM AUTHOR]

Heat treatment process is one of the key methods to improve the mechanical properties of age-hardening Al–Cu–Li alloy, and pre-stretching can further increase nucleation sites of precipitates by introducing dislocations. In this study, the effects of solution treatment, artificial ageing, and 4% pre-stretching on the microstructure evolution, mechanical properties, and fracture mechanism of extruded 2050 Al–Cu–Li alloy were investigated. The results indicated that the residual secondary phase, including Al 2 Cu and Al 2 CuLi, precipitated in hot extrusion were dissolved and a non-recrystallization characteristic for the 2050 alloy was presented after solution treated at 530 °C for 90 min. During artificial ageing at 150 °C, the precipitation sequence of the alloy without pre-stretching was: SSS → GP zone + δ′/β'→ θ' + T 1. Pre-stretching led to denser dislocations thus a higher nucleation rate of T 1 phase in compared with the alloy without pre-stretching. Additionally, the segregations of non-Cu atom at dislocations inhibited the formation of GP zones in the early ageing state, thereby providing sufficient Cu atoms for accelerating the growth of T 1 phases. After pre-stretched by 4% and aged at 150 °C for 12 h, a good combination of strength (YS = 671 MPa, UTS = 682 MPa) and ductility (EL = 10.3%) was obtained. The fracture mode changed from transgranular fracture to intergranular fracture with increasing ageing time due to the dislocation density and the distribution, size, and number density of the precipitates. [ABSTRACT FROM AUTHOR]

The influence of Zn addition on microstructure evolution and mechanical performance of a novel cast Al-Li-Cu-Mg alloy is studied in detail. The results reveal that Zn modifies the precipitation behaviors and improves the tensile strength effectively. As Zn content increases to 1 wt%, the precipitation of T 1 (Al 2 CuLi) phase is greatly enhanced at the expense of S′ (Al 2 CuMg) phase. Zn atoms are observed to enrich in T 1 phase by using high-angle annular dark field-scanning transmission electron microscope (HADDF-STEM), possibly attributed to some Cu atoms being substituted by Zn atoms. The precipitation of δ′ (Al 3 Li) is increased as Zn addition, suppressing the widening of δ′-precipitation-free zones. A more uniformly distribution of S'is also observed in the Zn-containing alloys. With the collaborative effect of both T 1 and δ′ precipitates, the optimal ultimate tensile strength of 504 MPa is obtained in 1 wt% Zn-containing alloy aged at 175 °C for 64 h, which is the highest value in cast Al-Li alloy field at present. • The alloys studied in this study are high Li-containing cast Al-Li alloys with low density. • The optimal Zn content significantly promotes content of T 1 precipitation. • The mechanism of Zn in aging process is analyzed in detail by microstructure characterization. • The UTS of 504MPa obtained in this study is the highest value in all the cast Al-Li-Cu alloys at present. [ABSTRACT FROM AUTHOR]