Search

2195 Al-Li alloy was deformed through extrusion followed by cold-rolling. The textures of the extruded plate and cold-rolled sheet after solutionization were investigated. The longitudinal strength and precipitates after T8 aging were measured and observed, respectively. Compared to those in the sheet, T1(Al2CuLi) precipitates in the extruded plate after T8 aging are non-uniform, and their incubation time is shorter. The extruded plate after solutionization is not recrystallized and contains 55.28% deformation textures of Brass and S. In the cold-rolled sheet after solutionization, massive recrystallization occurs and S component disappears. Due to the higher fraction of Brass and S textures with higher Schmid factor and lower equivalent sliding system number, the extruded plate possesses an yield strength not higher or even lower, but a tensile strength higher, than the cold-rolled sheet after solutionization. In addition, during the aging after pre-stretch, these textures promote T1 precipitation on preferred sliding planes of cold-rolled sheet and cause its higher yield strength and tensile strength after T8 aging.

In this work atomic-resolution techniques of high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM), energy-dispersive X-ray spectroscopy (EDXS)-STEM and first-principles calculations have been combined to study a hitherto unreported sandwich structure formed in aged samples of Al-Cu and Al-Cu-Au alloys. This sandwich structure comprises a stack of regularly spaced plates of metastable precipitate phases of GP zones, θ″ and θ′. Within the sandwich structure, the separation between the broad surface of θ′ and its adjacent GP zone, as well as that between two neighbouring GP zones, is always three {002}α planes. This sandwich structure is observed for θ′ precipitates of various thicknesses. Based on experimental results and calculations, it is inferred that the formation of the sandwich structure is induced by the θ′/Al interfacial segregation of Cu atoms, rather than the misfit associated with θ′ formation. In the sandwich structure formed in the ternary alloy, Au atoms distribute mainly in the central part of θ′ plate, but not at the θ′/Al interface or in the GP zone. Calculations confirm the experimental observations and further indicate that, energetically, Au atoms prefer to substitute for Cu, rather than Al, atoms within θ′.

The effect of cold rolling reduction (50%–90%) on the grain structures of solutionized 1445 Al–Li alloy sheet at 525–575 °C was investigated through electron backscatter diffraction (EBSD). Although the solutionization temperature is elevated to 575 °C, the sheet is not completely recrystallized. The main recrystallization model is subgrain coalescence and growth, and the non-recrystallization is due to the formed nano-sized Al3(Sc,Zr) dispersoids, which pin the grain boundaries, subgrain boundaries and dislocations. With increasing the cold rolling reduction, the fraction and size of the recrystallized grains in the sheet solutionized at 525 °C are decreased, but the fraction of the subgrains is increased, leading to a decrease in the fraction of the deformed structures. Meanwhile, the number fraction of high-angle boundaries (HABs) is increased. Due to the decreased fraction of the deformed structures and increased fraction of the HABs, the T8-aged 1445 Al–Li alloy sheet displays a decrease trend in the strength and heterogeneity with increasing the cold rolling reduction. At higher solutionization temperature of 575 °C, the fraction of the recrystallized grains and their size are obviously increased.

During the search for a highly sensitive sensor of CO2 gas molecule, the adsorption of CO2 gas molecule on both intrinsic and detected graphene sheets was studied by first-principles calculations. We explored that the CO2 gas molecule adsorption on the different elements X (B, N, P, Al) doped mono-vacancy graphene, the results showed that Al-MG was better than B-MG, N-MG and P-MG for the CO2 gas molecule with suitable adsorption strength and apparent band gap. Moreover, Al-MG had a chemical reaction with CO2 gas molecule and came into obvious charge transfers. So sensitivity to CO2 gas molecule made Al-MG was a promising candidate for highly sensitive gas sensor.

The tensile properties, microstructures and fracture behaviors of an Al-Zn-Mg-Cu alloy during ageing after solution treating and cold-rolling have been investigated. Tensile results show that high strength and acceptable ductility can be achieved simultaneously for the alloy. The enhanced strength, resulting from the combination of high-density dislocations, increased rolling textures, refined grains and nano-sized precipitates, changes with the precipitation characteristics and decreased dislocation densities. The improved ductility is attributed mainly to the decreased dislocation densities and meanwhile influenced by precipitation characteristics. The tensile fractographies are dominated by the dimple-induced transgranular fracture accompanied by small amount of intergranular fracture.

The effect of the thickness reduction on the intergranular corrosion (IGC) of under–aged Al–Mg–Si–Cu alloy sheets during cold–rolling is investigated. The accelerated corrosion test shows that the IGC susceptibility increases firstly and then decreases gradually with increasing the thickness reductions of the cold–rolled sheets. Microstructural observations indicate that the increased IGC susceptibility results from the transformation of the initial low–angle grain boundaries to high–angle ones, whereas its decrease correlates with the small–sized grains formed at the high–angle grain boundaries. Furthermore, the difficulty for removing IGC by cold–rolling increases gradually in the sequence of short–transverse, longitudinal–short and longitudinal–transverse grain boundary planes.

The influence of aging treatment on microstructures, tensile properties and corrosion properties of Al–Cu–Li alloy was investigated. The results show that the T8 duplex aging treatment was more effective than T6 and T8 single aging treatment in enhancing the tensile properties and improving the intergranular corrosion (IGC) resistance. Based on the microstructure observation, tensile test, electrochemical experiment and IGC measurement, the factors which affect the microstructures, tensile properties and IGC behavior changing of Al–Cu–Li alloy during aging treatments were discussed in detail.

The influences of annealing prior to solution treatment on the grain structure, subsequent aging precipitates, and intergranular corrosion (IGC) of Al-Cu-Li alloy (AA2050) sheet with T6 aging at 448 K (175 °C) were investigated. Annealing impedes the full recrystallization during solution treatment, increasing the population density of T1 (Al2CuLi) precipitates, but decreasing that of θ′ (Al2Cu) precipitates, of the aged alloy. Meanwhile, annealing leads to the heterogeneous distribution of T1 precipitates, increasing the alloy hardness, and decreasing the open-circuit potential of the aged alloy. With prolonged aging time, the corrosion mode of the aged AA2050 samples with and without annealing evolved in a similar manner. The corrosion mode as a function of aging may be summarized as local IGC with pitting and general IGC with pitting (following initial aging and under the underaged condition), pitting corrosion (later in the under-aging stage), pitting with slight IGC (near the peak-aged condition), and pitting with local IGC (under the overaging condition). The annealing treatment hinders IGC propagation on the rolling surface while accelerating the IGC on transverse surfaces.

Hot compression tests of 2050 Al–Li alloy were performed in the deformation temperature range of 340–500 °C and strain rate range of 0.001–10 s–1 to investigate the hot deformation behavior of the alloy. The effects of friction and temperature difference on flow stress were analyzed and the flow curves were corrected. Based on the dynamic material model, processing map at a strain of 0.5 was established. The grain structure of the compressed samples was observed using optical microscopy. The results show that friction and temperature variation during the hot compression have significant influences on flow stress. The optimum processing domains are in the temperature range from 370 to 430 °C with the strain rate range from 0.01 to 0.001 s–1, and in the temperature range from 440 to 500 °C with the strain rate range from 0.3 to 0.01 s–1; the flow instable region is located at high strain rates (3–10 s–1) in the entire temperature range. Dynamic recovery (DRV) and dynamic recrystallization (DRX) are the main deformation mechanisms of the 2050 alloy in the stable domains, whereas the alloy exhibits flow localization in the instable region.

Microstructural evolution of friction stir welded 2099 Al Li alloy was evaluated. Friction stir welding (FSW) resulted in significant grain refinement, dissolution of original phases T 1 (Al 2 CuLi) and δ ′ (Al 3 Li), and precipitation of ultrafine δ ′ phases in the nugget zone (NZ). In the heat affected zone (HAZ), heavy precipitation of T 1 phases led to a peak hardness of 105 HV. A strong rotated Cube texture {013} 〈100〉 was obtained in the base metal (BM). After FSW the NZ was characterized by shear texture {111} 〈110〉, while Bass texture {110} 〈112〉 and S texture {123} 〈634〉 were developed in the thermo-mechanically affected zone (TMAZ). Compared with the BM, the dislocation density was decreased in the welding zones, which resulted from recovery and recrystallization.

The intergranular corrosion (IGC) susceptibility of 2024 Al alloy during re–ageing after solution treating and cold–rolling was investigated by accelerated corrosion testing, open circuit potential testing, transmission electron microscopy and scanning electron microscopy. The absence of IGC in both the peak–re–aged and over–re–aged samples is related to the dislocation pile–ups which prevent the supersaturated solutes from diffusing into the grain boundaries and precipitating the continuous S–Al2CuMg phase. The aggregated pitting corrosion in the over–re–aged samples arises from the S–phase precipitates on the dislocation cell walls which accelerate the anodic dissolution of the cell interiors.

The influence of pre-deformation on aging precipitates of three near peak-aged Al–Cu–Li alloys, 1460 alloy with a low Cu/Li ratio (1.46), 2050 alloy with a high Cu/Li ratio (4.51) and 2A96 alloy with a medium Cu/Li ratio (2.97), was investigated. The strength of the aged alloys is enhanced by the pre-deformation. The effectiveness of pre-deformation on precipitates is dependent on the alloy’s composition. With increasing the pre-deformation, the population density of T1 (Al2CuLi) precipitates increases in all three Al–Cu–Li alloys and their diameter decreases in 2050 and 2A96 alloys, and the greatest effectiveness is observed in 2A96 alloy. The pre-deformation also increases the population density of θ′ (Al2Cu) precipitates and decreases their diameter in 2050 and 2A96 Al–Li alloys, but the effectiveness is smaller compared to that on T1 precipitates. In 1460 alloy subjected to two-step aging at 130 °C for 20 h followed by 160 °C for 12 h, the main precipitates are δ′ (Al3Li). At 2%–6% pre-deformation, GP-I zones form and pre-deformation displays little influence. Eight percentage pre-deformation promotes θ″/θ′ precipitation and increases their population density.

Predeformation on tensile properties and microstructure of three Al-Cu-Li alloys, 1460, 2050 and 2A96 was investigated. The strength of the alloys is enhanced by the predeformation. Meanwhile, predeformation impacts the precipitation of T1 (Al2CuLi) and θ′(θ′′) (Al2Cu) phases. The precipitation (nucleation rate) of T1 is accelerated by the predeormation, and the effect is increased with the predeformation degree. While, effect on θ′(θ′′) precipitation is dependent on the alloy composition feature. In the 2A96 alloy with a medium Cu/Li ratio, it is decelerated by the predeformation. In the 2050 alloy with high Cu/Li ratio and 1460 alloy with low Cu/Li ratio but subjected to two-step aging at 130°C and 160°C, the θ′(θ′′) precipitation is accelerated at lower predeformation but decelerated at higher predeformation.

Generating or recycling water and resources from wastewater other than just treating wastewater is one of the most popular trends worldwide. Photosynthetic bacteria (PSB) wastewater treatment and resource recovery technology is one of the most potential methods. PSBs are non-toxic and contain lots of value-added products that can be utilized in the agricultural and food industries. They are effective to degrade pollutants and synthesize useful biomass, thus realizing wastewater treatment, bioresource production, and eliminating waste sludge. If all the nutrients in wastewaters could be bio-converted by PSB, then pollutant reductions and economic benefits would be achieved. This review paper firstly describes and summarizes this technology, including PSBs classification, metabolism, and the market application. The feasibility, technical procedures, bioreactors, pollutant removal, and bioresource production are also summarized, compared and evaluated. Issues that concern the advantages and industrialization of this technologies at the plant scale are also discussed.

The microstructural evolution and mechanical properties of a new Al–3.8Cu–1.2Li–0.4 Mg–0.4Zn–0.4Ag–0.3Mn–X alloy treated at different solution temperatures were investigated. The grain size was measured in optical micrograph (OM). The residual particles and the major precipitates were identified by electron probe microanalysis (EPMA), scanning electron microscopy (SEM) and transmission electron microscope (TEM), respectively. The results show that the peak strength appears at 530 °C/1 h + T6(165 °C/20 h) and the values are 566.2 MPa (tensile strength) and 538.2 MPa (yield strength) with the elongation of 6.5 %. The strength of the alloy increases rapidly with the amount of the precipitates T1 and θ′ increasing when the solution temperature is 530 °C. The increase in density of precipitates is resulted from the residual particles Al2Cu, and particles enriched with Cu, Mg, Zr and Ag dissolve into matrix gradually with the solution temperature increasing. Finally, the number of precipitates decreases and part of the grain boundary weakens with a further increase in solution temperature from 540 to 550 °C, leading to a decline of strength.

Usually, underaged or peakaged Al-Mg-Si-Cu alloys are susceptible to intergranular corrosion (IGC), whereas overaging can eliminate the IGC susceptibility. However, it is found that the IGC susceptibility can be formed again when the alloys are heavily overaged further. The IGC susceptibility in the heavily overaged condition results from the anodic dissolution of the precipitation-free zones (PFZs) with the closely-neighbored grain boundary Q-phase (Al 4 Mg 8 Si 7 Cu 2 ) precipitates acting as the continuous cathodes. The formation of the closely-neighbored grain boundary precipitates is attributed to their further growth via dissolving the adjacent matrix precipitates based on the Ostwald ripening process during the long-time overaging.

The microstructural evolution of a Mg, Ag and Zn micro-alloyed Al–3.8Cu–1.28Li (mass fraction, %) alloy ingot during two-step homogenization was examined in detail by optical microscopy (OM), differential scanning calorimetry (DSC), electron probe micro-analysis (EPMA) and X-ray diffraction (XRD) methods. The results show that severe dendritic segregation exists in the as-cast ingot. There are many secondary phases, including T B (Al 7 Cu 4 Li), θ (Al 2 Cu), R (Al 5 CuLi 3 ) and S (Al 2 CuMg) phases, and a small amount of (Mg+Ag+Zn)-containing and AlCuFeMn phases. The fractions of intermetallic phases decrease sharply after 2 h of second-step homogenization. By prolonging the second-step homogenization time, the T B , θ, R, S and (Mg+Ag+Zn)-containing phases completely dissolve into the matrix. The dendritic segregation is eliminated, and the homogenization kinetics can be described by a constitutive equation in exponential function. However, it seems that the AlCuFeMn phase is separated into Al 7 Cu 2 Fe and AlCuMn phases, and the size of Al 7 Cu 2 Fe phase exhibits nearly no change when the second-step homogenization time is longer than 2 h.

The hot deformation behavior of 2060 alloy has been studied using thermal simulation test, EBSD technique and transmission electron microscopy. The flow stress could be described by a Zener-Hollomon parameter in hyperbolic sine function with the hot deformation activation energy of 205 kJ/mol. Dynamic recovery is the main dynamic soften mechanism of 2060 alloy. The relative volume fraction of subgrains increases from about 30% to 90% as the temperature rises from 350 °C to 400 °C. When the temperature is higher than 400 °C, both the relative volume fraction of the deformed grains and subgrains remain steady. The processing maps are similar in the strain ranging from 0.1 to 0.5, and the unsafe domains increase with the increase of strain. The optimum hot-working condition for 2060 alloy is 380–500 °C and 0.01–3 s−1.

In this study, the crack-free parts have been successfully fabricated by Laser Engineered Net Shaping (LENS) based on a Ni-Co-Cr-Al-Ti-Fe-Nb-Mo nickel-based superalloy powder, and its microstructure evolution and formation mechanism were investigated. The results revealed that the microstructure along the deposition direction is stray dendrites with disordered growth direction in the bottom two layers, epitaxially growing elongated columnar dendrites dominating the whole cross-section of the as-deposited, fine equiaxed grains in the upper of the last layer, respectively. Moreover, it can be found that although the as-deposited layer contains many high angle grain boundaries, no cracks can be observed. According to the chemical composition and phase analyses, it can be concluded that crack-free microstructure is ascribed to the homogeneous distribution of elements and the formation of single-phase γ in the as-deposited. The effect of 1.34 Al, 1.37 Ti, 0.41 Nb, and 0.50 Mo (wt%) on the formation of low melting point substances is discussed. The room-temperature ultimate tensile strength is about 807 MPa, while the high-temperature ultimate tensile strength is 654 MPa.

To develop super-high strength Al–Li alloy, the microstructures and mechanical properties of Mg, Ag and Zn micro-alloyed Al–(3.2–3.8)Cu–(1.0–1.4)Li alloys (mass fraction) with T8 temper were studied. The results showed that 1% of lower Li content restricted the strengthening effect of increasing Cu content, while simultaneous increase in Cu and Li contents contributed effectively to the enhancement of strength. The alloys were mainly strengthened by plenty of fine and well dispersed T1(Al2CuLi) precipitates. There were also some minor precipitates of θ ′(Al2Cu) and δ′(Al3Li), which became less in number density, even disappeared during the aging process. Meanwhile, higher Li content favored the formation θ ′ and δ ′ and a small amount of S′(Al2CuMg) phases. In addition, strengthening effect and microstructure variation were analyzed through total non-solution mole fraction of Cu and Li and their mole ratio. To obtain Al–Li alloy with super-high strength, the total mole fractions of Cu and Li should be increased, and their mole ratios should also be kept at a certain high level.

A novel production method of the Al–Mg–Si–Cu cold-rolled sheets was proposed in the present work, which was characterized by solution treatment substituting for conventional intermediate recrystallization annealing before the final cold-rolling of the sheets. After further solution and peak-ageing treatment, the newly produced 6061 Al sheets exhibited markedly higher mechanical properties (ultimate tensile strength (UTS): 454 MPa, yield strength (YS): 438 MPa and elongation (El): 13%) than those of the conventionally produced ones (UTS: 384 MPa, YS: 368 MPa and El: 11%). The quantitative estimation of strengthening mechanisms indicated that the increased peak-ageing strength of the newly processed 6061 alloy sheets was mainly attributed to their high average Taylor factor value, which resulted from the P texture with high volume fraction. Furthermore, the fracture characteristics of the newly produced and peak-aged 6061 alloy sheets were dominated by dimple induced cracking accompanied by small amount of intergranular cracking.

The present work aims to clarify the formation of the W phase (AlCuSc) and its formation time in the high Cu content alloy with Sc addition. The microstructure evolution during the two-step homogenization annealing process was investigated in the 1469 Al–Cu–Li–Sc alloy. No evidences of the Al3Sc phase and the W phase were found in the solidification structure. The arrays of the W phases were found to form after homogenization. The AlCu phases with traces of Sc that formed during solidification suppose to be the precursor of the W phases, and then transform into the W phases by consuming the Sc atoms that fixed in the supersaturate solid solution. The formation of the W phase inhibits the precipitation of the Al3Sc phase. A corresponding model of the W phase formation mechanism is proposed.

A novel thermo-mechanical treatment consisting of conventional pre-aging, cold-rolling and re-aging was developed to enhance the tensile properties and intergranular corrosion resistance of Al–Mg–Si–Cu alloys simultaneously. The thermo-mechanically treated 6061 Al sheets exhibit higher ultimate tensile strength and yield strength (being 466 MPa and 451 MPa) than those of the conventionally peak-aged alloys (being 365 MPa and 347 MPa), and meanwhile have no intergranular corrosion susceptibility and good elongation of 8.1%. Based on the microstructure evolution during the thermo-mechanical treatment, the factors that enhance the tensile properties and intergranular corrosion resistance of the treated sheets are discussed in detail.

The influence of 0.72 pct Zn addition on the tensile properties of Al-2.7Cu-1.7Li-0.3Mg alloys was investigated. Their intergranular corrosion (IGC) dependence on aging [T6 type at 423 K (150 °C) and 448 K (175 °C) and T8 type at 423 K (150 °C)] time was studied. An IGC diagram associated with aging process was established. The addition of 0.72 pct Zn enhanced the strength of the Al-Li alloy with T6 type aging at 448 K (175 °C). With aging process, the corrosion mode of the T6-aged Al-Li alloys was changed in the following order: pitting and local IGC (initial aging stage), general IGC (underaging stage), local IGC (near peak-aging stage), and pitting (overaging stage) again. The IGC depth was increased first and then decreased with aging time extension. The corrosion potential change of grains and the microstructure variation were used to explain the IGC sensitivity of the Al-Li alloy with different tempers. Meanwhile, 0.72 pct Zn addition decreased the IGC sensitivity of the Al-Li alloy, especially the T6-aged Al-Li alloy.

A novel thermo-mechanical treatment, composed of under-aging, cold-rolling and re-aging, has been developed to improve the strength and ductility of Al–Mg–Si–Cu alloys pronouncedly. The thermo-mechanically treated 6061 Al sheets exhibit much higher ultimate tensile strength and yield strength (being 560 MPa and 542 MPa, respectively) than those of the conventional peak-aged sheets (being 365 MPa and 348 MPa, respectively), while maintaining rather good elongation to failure and uniform elongation (being 8.5% and 7%, respectively). The microstructure analyses show that the high strength is attributed to a combination of precipitation strengthening, dislocation strengthening, sub-structure strengthening and high Taylor factor value and the good ductility is attributed to both the recovery process and the re-precipitation of the GP zones. Furthermore, the contributions of different strengthening mechanisms are quantitatively estimated.

The influence of aging (T6 at 150°C and175°C, T8 at 150°C) and 0.72% Zn addition on the mechanical properties, microstructures and intergranular corrosion (IGC) behavior of Al-2.7Cu-1.7Li-0.3Mg alloys was investigated. With 0.72% Zn addition, the strength of the Al-Li alloy was increased. As the aging time was extended, the corrosion type of the studied Al-Li alloys was changed in the following order: pitting, local IGC, general IGC, local IGC and pitting again. For the T6 temper, as the aging temperature was elevated from 150°C to 175°C, the aging time period for IGC appearance was shortened. The pre-deformation before aging (T8 temper) also greatly shorten the aging time period for IGC. Meanwhile, the addition of 0.72% Zn decreased the IGC sensitivity and shortened the aging time period for IGC.

Microstructure evolution and mechanical properties of a 1469 alloy and a Sc-free1469 type alloy were examined. SEM observation indicates that AlCuSc ternary phases (W) are formed after homogenization annealing, and cannot be dissolved during the following heat treatments. These coarse particles consume abundant Cu atoms from the Al matrix that are available for solutioning, which results in the decrease of precipitation of the T1 phase during aging treatment. The W phase has negative effects on the examined alloy’s mechanical properties. The tensile strength of Sc-added alloy is 40MPa lower than that of the Sc-free alloy. The formation of the W phase has a close relationship with Cu/Sc ratio, which shows the importance of controlling the concentration of Cu and addition of Sc. Formation of W phase suppress the effect of precipitation hardening of the T1 phase in high strength Al-Cu-Li alloys

In this work, a new ultra-high strength Al-Cu-Li alloy was investigated. The ultimate strength, yield strength and elongation of the newly designed alloy by artificial aging are 647.2MPa, 609.4MPa and 7.3% respectively. Among the main strengthening phases of T1, θ′ and S′ in the experimental alloys, T1is the dominant one. The combined addition of Mg and Ag promoted the precipitation of T1and increased the strength of the new alloy greatly. Zn had a similar effect as Ag during the aging strengthening progress, when added with Mg. Among the three micro-alloying elements, Mg, Ag and Zn, Mg had the strongest influence on age strengthening. Compared with the combined additions of (Mg +Ag) and (Mg + Zn), (Ag + Zn) had the weakest influence on aging strengthening. Pre-deformation before aging promoted the precipitation of T1 phase which weakened the influence of micro-alloying elements (Mg, Ag and Zn) on strengthening the alloys and minished the strength difference between alloy containing (Mg + Ag + Zn) and alloys containing two of them.

The microstructure, tensile property and fracture toughness of Al-Li alloy 2397-T87 rolled plate were investigated by optical microscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, tensile and plane-strain fracture toughness tests. The results show that a pronounced texture variation through the plate thickness was found. Near the surface, Goss texture dominated. While in the center of the plate, typical β fiber texture and a scattering of cube texture were observed. And the subsurface layer exhibited a very weak texture. From the center to the subsurface, the fraction of β fiber texture and cube texture decreased. In contrast, the fraction of shear type texture reaching the maximum in subsurface layer increased. The tensile properties in different layers along the thickness direction were inhomogeneous. The strengths near the surface were lower than those in the center. And the through-thickness strength properties variation in the rolling direction was more remarkable than that in the long transverse direction. In the same thickness layer, the fracture toughness and the strengths were anisotropic. The strengths in the rolling direction were higher than those in the long transverse direction and the short transverse direction, and the strengths in the short transverse direction were the lowest. The fracture toughness in L-T orientation was the highest, followed by that in T-L orientation, and the fracture toughness in S-L orientation was the lowest.

The microstructure and mechanical properties of high performance Mg-2.6Sm-1.3Gd-0.6Zn-0.5Zr (wt.%) alloy was investigated. The alloy was mainly composed α-Mg and (Mg,Zn)3(Sm,Gd)1 eutectic phase in the as-cast state. After solution treatment at 510 °C for 4 h and subsequent aging at 200 °C, the alloy exhibited remarkable mechanical properties. The ultimate tensile strength, yield strength and elongation of the alloy at peak-aged state were 282, 185 MPa and 6.1% at room temperature. These good mechanical properties were mainly attributed to the fine microstructure and fine metastable phase precipitates in the matrix during aging at 200 °C for 32 h.

The effect of Zinc (Zn) additions (0, 0.3, and 0.6 wt.%) on the microstructure and mechanical properties of Mg–3Sm–0.5Gd–0.5Zr (wt.%) alloy has been investigated by optical microscopy, scanning electron microscope, X-ray diffraction and transmission electron microscopy. The peak-aged Mg–3Sm–0.5Gd–0.3Zn–0.5Zr alloy exhibits an good ultimate strength, of above 270 MPa. The plate precipitates β ′ are formed on the prismatic plane of the matrix in peak-aged state, which contributes to the strengthening of the alloy. The peak-aged Mg–3Sm–0.5Gd–0.6Zn–0.5Zr alloy precipitates basal plane phase γ , which has a bad effect on the mechanical property.

The fatigue crack initiation and early propagation behavior of 2A97 Al–Li alloy was studied. The smooth specimens were fatigued at room temperature under constant maximum stress control when stress ratio (R) is 0.1 and frequency (f) is 40 Hz. Microstructure observations were examined by optical microscopy, transmission electron microscopy, scanning electron microscopy and electron back scattered diffusion, in order to investigate the relationship between microstructure and fatigue crack initiation and early propagation behavior of 2A97 alloy. The results show that the fatigue cracks are predominantly initiated at inclusions and coarsen secondary phases on the surface of 2A97 alloy. The fatigue crack early propagation behavior of 2A97 alloy is predominantly influenced by the interactions between grain structure and dislocations or persistent slip bands (PSBs). When the misorientation of two neighbouring grains is close to the orientations of the favorable slip plane within these two grains, high-angle grain boundary severely hinders the PSBs passing through, and thus leads to crack bifurcation and deflection.

The influence of the solution treatment on microstructures and mechanical properties of 2099 Al–Li alloy was investigated by means of optical microscopy, scanning electron microscopy, transmission electron microscopy and tensile properties measurement. With increasing solution temperature, the quantity of primary particles in the alloy decreased, and the degree of recrystallization gradually increased, leading to softening of solution treated alloy. Dissolution of primary particles in the solution treatment process promoted δ ′ and T 1 phases to precipitate during sequent aging treatment resulting in increase of strength. The number of T 1 phases increased to peak value when the alloy was solution treated at 540 °C because almost no further dissolution of Cu-containing particles occurred at higher temperature. However, exorbitant solution temperature caused the drastic increase in the size and quantity of recrystallized grains that softened the alloy. Thus, mechanical properties of aged alloy were determined by two mechanisms: precipitation strengthening and solution softening. Compared with solution temperature, solution time had less effect on microstructures and mechanical properties of alloy. The suitable solution treatment for 2099 Al–Li alloy was 540 °C for 1 h, treated by which the yield strength of the aged alloy was 604 MPa with the elongation of 7.9%.

In order to improve the intergranular corrosion (IGC) resistance of Al–Mg–Si–Cu alloys without strength loss compared to that of the T6 temper, a new two-step aging treatment has been developed in the present study. The two-step aging treatment includes pre-aging at a relatively higher temperature for a shorter time and then re-aging at a lower temperature for a relatively longer time. The microstructural observation shows that after the optimized two-step aging of 180 °C/2 h+160 °C/120 h, the microstructural characteristics of the alloy combines the matrix of high number density β″ precipitates and grain boundaries of discretely distributed GBPs. The type of microstructures is responsible for the improvement of IGC resistance of the alloy without strength loss.

In order to study the workability of a Al-Cu-Li alloy, isothermal hot compressive deformation was investigated in the temperature range of 350-500 °C at strain rates in the range of 0.01-10/s up to a true strain of 0.9 on Gleeble-1500 mechanical testing machine. The flow stress increased rapidly to a peak value. The peak stress decreased with increasing deformation temperature and decreasing strain rate. The effects of strain rate and temperature on hot deformation behavior can be represented by a Zener-Hollomon parameter including an Arrhenius term. The influence of the strain has also been incorporated in the constitutive equation and four material constants α, n, A, and the activation energy Q were calculated by compensation of strain. The proposed constitutive equation (considering the compensation of strain) gives an accurate description for the flow stress of the Al-Cu-Li alloy.

In this study, microstructures and properties of 2099 Al-Li alloy were investigated during the thermo-mechanical processing. Treated by two-step homogenization treatment (12 h at 510 °C + 36 h at 530 °C), the coarse dendritic structures cannot be observed in the alloy. At the same time, the level of grain boundary segregation was lowered, and a few of small AlCuFeMn/AlCuMn particles remained at the grain boundaries. Following homogenization treatment, the alloy was extruded at 470 °C. During extrusion process, dynamic recrystallization occurred in the surface layer of alloy, and the depth of dynamic recrystallized layer increased with solution treating at 540 °C. The central zone of alloy with solution treatment exhibited {111} and {111} textures, while {112} texture presented at the surface zone. The corresponding central hardness of alloy in central zone was 95 HV, and the surface hardness was 120 HV. After solution treatment, two-step aging treatment was followed. In the peak-aged condition (12 h at 121 °C + 48 h at 152 °C), a large amount of T1 phases as well as δ′ phases precipitated in the matrix. The tensile strength, yield strength and elongation of alloy on peak aging were 613 MPa, 575 MPa, and 7.9%, respectively. The SCC susceptibility of alloy decreased with aging time, and the strength loss rate of alloy on over-aging was 5.5%.

During ageing at 200 °C, a trace (0.2 wt%) addition of Ge to a base Al–3.5Cu–0.4Mg alloy resulted in anomalous precipitation processes by stimulating the formation of nanoscale precipitate and suppressing the formation of S′(Al2CuMg) precipitate. This behavior was demonstrated to be closely related to the preferential Mg–Ge cluster which formed in the early ageing stage. The increased hardening response and enhanced hardness in Ge-containing alloy were due to the rapid precipitation of high density of fine nanoscale precipitate. The transmission electron microscopy (TEM) investigation indicated that nanoscale precipitate, θ′ (Al2Cu), θ′II (Al2Cu) and σ (Al5Cu6Mg2) precipitates could coexist in Al matrix for prolonged ageing at 200 °C. And the nanoscale precipitate was demonstrated to own 〈001〉α needle-shaped morphology and be enriched with aluminum, copper, magnesium and germanium. The Mg/(Cu+Ge) atomic ratio in them is close to 1:1. High-resolution TEM observation indicated that the nanoscale precipitates appeared to be coherent with Al matrix and their orientation relationship is 〈100〉nano//〈100〉Al and {010}nano//{010}Al. A modified structure with composition of Al10Mg3Cu3−xGex (0

Effects of heat treatment processes on tensile properties of 2A97 Al-Li alloy were investigated. The results show that one new heat treatment process which was developed from traditional T8 temper can effectively improve the tensile properties of Al-Li alloy. In the peak-aged condition, a large quantity of fine T1 dispersedly precipitated in the matrix. At the same time, few secondary phases precipitated at the grain boundaries, and precipitation-free zone was unobvious. The corresponding tensile strength, yield strength and elongation of alloy were 597 MPa, 549 MPa and 7.4%, respectively. In addition, BP neural network model was developed for prediction of the tensile properties of alloy subjected to different heat treatment processes. A very good correlation between experimental and predicted results was obtained, which indicates that the BP neural network can be used for the prediction of tensile properties of 2A97 Al-Li alloy.