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Regenerated silk fibroin (RSF), made from discarded silk cocoons, can be processed into regenerated silk fibers by a simple, inexpensive, and environmentally friendly wet-spinning process. However, the breaking strength and toughness of most RSF fibers are lower than those of natural silk. In this study, Ag nanoparticles (NPs) of different sizes were introduced into RSF to form RSF/AgNPs hybrid fibers by wet spinning. The effects of AgNPs of different sizes on the mechanical properties and structure of the hybrid fibers were investigated. The results demonstrated that the mechanical properties of hybrid fibers were significantly improved, especially the breaking strain, after the addition of four different sizes of AgNPs. With the reduction in AgNPs size (2–60 nm), the breaking strength and breaking strain of hybrid fibers tended to increase. The results showed that the hybrid fibers containing 2 nm AgNPs were remarkable, with excellent mechanical properties and toughness, and the breaking strain reached 138.27%, which was far greater than blank RSF fibers (15.02%) and even natural silk (about 21%). The S-FTIR and WAXD showed that, compared with the larger AgNPs, the smaller AgNPs contributed more to the formation of silk fibroin β-sheet and crystallinity, and reduced the β-crystallite size. This study is helpful to understand the relationship between the size of nanoparticles and the mechanical properties of hybrid fibers. [ABSTRACT FROM AUTHOR]

• Mechanical properties of Al-Cu-Li alloy were enhanced via optimizing Ag/Mg ratios. • The variation of Ag/Mg ratios modifies the precipitation sequence of the alloy. • High relative volume fraction and large size of T 1 phases lead to improved strength. • The coexistence of T 1 , θ́, and Ś phases contributes to high ductility. Wrought Al-Cu-Li alloys usually necessitate pre-stretching to improve their mechanical properties. A novel insight into enhancing the mechanical properties of a non-stretched Al-Cu-Li alloy has been proposed by optimizing the Ag/Mg ratios and investigating their impact on precipitation behavior. Four alloys having Ag/Mg ratio between 0.24–5.63 and a combined Ag + Mg content of 1.1 wt% were designed. The results indicated that the strengthening precipitates were mainly plate-like T 1 and θ́ precipitates. With decreasing Ag/Mg ratios from 5.63 to 1.87, T 1 phase fraction increased from 28 % to 39 %, and the corresponding θ́ phase fraction reduced from 72 % to 61 %. Comparatively, S' phases dominated the microstructure while impeding the formation of θ' and T 1 precipitates at Ag/Mg ratio was 0.24. The alloy at Ag/Mg ratio of 0.95 had optimum mechanical properties owing to T 1 , Ś, and θ́ phases uniform dispersion within the matrix, among which T 1 had the highest volume fraction (48 %). [ABSTRACT FROM AUTHOR]

Herein, the effects of Zn/Y and Zn/Gd addition on microstructural evolution and mechanical properties of the superlight Mg–14Li‐based alloy are investigated. The results show that Mg–14Li‐based alloys are characterized by predominantly single β‐Li phase. Zn/Y addition leads to the introduction of homogeneous distribution of Mg3Zn3Y2 (W phase), Mg2Zn11, and MgLiZn phases. With the strengthening effect of grain refinement and a large number of precipitates, the mechanical properties of Mg–14Li‐based alloy are improved, whereas MgGd3, MgGd, Mg2Zn11, and GdZn5 phases appear with the addition of Zn/Gd, which enhance the Mg–14Li‐based alloy significantly due to grain refinement strengthening, the second phase strengthening, and solid solution strengthening. After hot extrusion, dynamic recrystallization (DRX) significantly refines β‐Li into equiaxed grains, and broken precipitated phases are distributed along the extrusion direction. Mechanical properties of those alloys are improved because of grain refinement and distributed precipitates. [ABSTRACT FROM AUTHOR]

Cast Al-Li alloys show attractive potential for application in the field of manufacturing large-size and complex parts as a result of profound weight reduction and good fluidity. However, the ductility and strength of sand-cast Al-Li alloys are relatively poor due to the low cooling rate of sand casting. In this study, Sc and Ti were added to sand-cast Al-Li-Cu-Mg-Zr casting alloy to investigate the microstructure evolution and tailor the final performance for the first time. The results showed that grain decreased from 189 µm to 56 µm and the needle Cu-rich phase increased in the vicinity of grain boundaries as the total element content of Sc and Ti increased. After aging at 175 °C, the enrichment of the T 1 and S′ phases, the finer δ′, the higher number density of core-shell composites, and the narrowed δ′-precipitation free zones (δ′-PFZs) were stimulated by Sc and Ti, leading to a significant increase in strength of the peak-aged alloy. The SZT alloy exhibits the best yield strength of 359 MPa and ultimate tensile strength of 452 MPa with an adequate elongation of 4.6 %. In addition, a Li-rich zone was observed and intersected with T 1 phase, which provided a new precipitation path for Li atom diffusion and nucleation of T 1 precipitates. The present study suggests that microalloying with Sc and Ti is expected to be an effective strategy to simultaneously improve the strength and ductility of sand-cast Al-Li alloys. • The effect of Sc and Ti on the microstructure evolution of strengthening phases is analyzed. • A good combination of strength and elongation is obtained by the combined addition of Sc and Ti. • The contributions from different strengthening mechanisms for peak-aged Al-Li-Cu-Mg-Zr alloy were studied in detail. [ABSTRACT FROM AUTHOR]

• Precipitation microstructures and mechanical properties of Al-2Li-2Cu-0.5 Mg-0.15Sc-0.1Zr-0.1Ti alloy aged at 175 °C are investigated. • The precipitates of alloy aged at 175 °C mainly consisted of T 1 , δ′, core–shell phase, S′ and cubic phase. • The cubic phase was transformed from Al 6 Cu 5 Li 2 to Al 6 Cu 5 Mg 2 with the aging time increasing from 8 h to 64 h. The microstructure evolution corresponding to the mechanical properties of cast Al-2Li-2Cu-0.5Mg-0.15Sc-0.1Zr-0.1Ti alloy aged at 175 °C was investigated, especially in the identification and variation of the cubic phase. The yield strength and ultimate strength of the peak-aged alloy reach 449 MPa and 502 MPa, respectively. From the transmission electron microscopy characterization, it was found that the precipitates primarily consisted of the cubic phase, T 1 (Al 2 CuLi), S′(Al 2 CuMg), core–shell particles and δ′(Al 3 Li) phases. Longer exposure to temperature changed the composition from Al 6 Cu 5 Li 2 to Al 6 Cu 5 Mg 2 , and these two phases are in competition with the T 1 and S′ phases. [ABSTRACT FROM AUTHOR]

Abstract This work was undertaken to investigate the influence of independent and combined additions of Mg and Sc on the microstructure, mechanical properties, and thermal stability of cast Al-2Li-2Cu-0.2Zr base alloy after thermal exposure. All studied alloys were exposed at 100 °C for 1000 h after a prior artificial ageing of 24 h at 150 °C to simulate the thermal exposure under service conditions. A significant increase in strength took place in all alloys, accompanied by different variations of toughness as a result of exposure. It is proposed that the toughness reduction in base Al-2Li-2Cu-0.2Zr alloy should be primarily attributed to the precipitation of θ′′/θ′ (Al 3 Cu/Al 2 Cu) plates together with complementary nucleation and coarsening of δ′ (Al 3 Li) particles. Addition of Mg has a pronounced effect on the competitive precipitation behavior, which will suppress the precipitation of θ′′/θ′ plates and encourage formation of S′ (Al 2 CuMg) phase. Significant grain refinement and increased Al 3 (Li, Sc, Zr) precipitation was obtained with minor Sc addition, contributing to the significant enhancement of ductility. Sc addition is revealed to promote the precipitation of refined θ′′/θ′ plates, primarily contributing to the significant strength enhancements. The additions of Mg and/or Sc could efficiently improve the strength and thereby reduce the susceptibility to exposure embrittlement of the base alloy during exposure. An excellent combination of strength (YS = 377 MPa, UTS = 478 MPa) and ductility (EL = 8.4%) after exposure could be obtained in the alloy with combined Mg and Sc addition. Graphical abstract Image 1 Highlights • Microstructural stability of cast Al-Li-Cu alloys was investigated. • Mg addition greatly retards the precipitation of θ′′/θ′ during exposure. • Sc addition synchronously improves the alloy strength and toughness. • The highest UTS of 497 MPa is obtained. [ABSTRACT FROM AUTHOR]

As a kind of cast aluminum alloy with high strength, Al–Li–Cu–Mg series alloys exhibit desirable stiffness and formability, while a limited investigation has discussed the influence of cooling rate on microstructure and mechanical properties of these alloys. In this work, the effect of cooling rate during casting on microstructure evolution and mechanical properties of cast Al–2Li–2Cu-0.5Mg-0.15Sc-0.1Zr-0.1Ti alloy was investigated using a step-like iron mold. The results showed that the increased cooling rate refined the grain size and augmented the volume fraction of second phase in the as-cast microstructure. In the aging process, the rapid cooling rate markedly promotes precipitation and suppresses coarsening of the δˊ(Al 3 Li), T 1 (Al 2 CuLi) and Sˊ(Al 2 CuMg) phases, which plays a vital role in enhancing strength of the peak-aged alloy. In addition to diffusion and vacancy mechanisms, a Li-rich zone offers a new precipitation pathway for T 1 precipitates. Notably, the rapid cooling rate of 16.1 °C/s significantly facilitated the formation and inhomogeneous distribution of the cubic σ(Al 6 Cu 5 Mg 2) phase, which competed with the T 1 and Sˊ phases for Cu and Mg atoms. Finally, the formation mechanism of the σ phase under different cooling rates was discussed, and the strengthening and fracture mechanisms were quantified. The present work is expected to enlighten the understanding of the microstructure evolution of Al–Li alloys with varied cast cooling rates. [ABSTRACT FROM AUTHOR]

In third-generation Al–Cu–Li alloys, T 1 , S', and θ' precipitates are the primary strengthening phases, and the strength-ductility synergy of the alloys depends strongly on their precipitation behavior. This study aimed to regulate the precipitation behavior among these precipitates by optimizing Ag/Mg ratio in Al–Cu–Li alloys, and its influence on mechanical properties and fracture mechanism was investigated. To this end, four alloys were designed with a total content of 1.1 wt% of Ag and Mg, and an Ag/Mg ratio ranging from 0.24 to 5.63. The results shows that an increase in the Ag/Mg ratio dramatically accelerated the ageing process and shortened the peak-ageing time. At 150 °C, the precipitation sequence of alloys with an Ag/Mg ratio below 0.95 was SSS→GPB zone +δ′/β'→S'+T 1 , which transformed into SSS→GP zone +δ′/β'→θ'+T 1 when the Ag/Mg ratio was above 1.87. The T 1 , S', and θ' precipitates coexisted and were dispersedly distributed among studied alloys with an Ag/Mg ratio ranging from 0.95 to 1.87. An Ag/Mg ratio of 1.87 resulted in the fastest ageing hardening response and the highest strength (YS = 705 MPa, UTS = 717 MPa) because of the highest volume fraction of T 1 precipitates. Moreover, the fracture mode changed from transgranular fracture to intergranular fracture with increasing Ag/Mg ratio due to the difference in distribution and number density of these precipitates between the matrix and grain boundary. [ABSTRACT FROM AUTHOR]

This paper reports the impacts of direct feeding silkworms with different nanoparticles (Cu, Fe, and TiO 2 ) on the morphology, structures, and mechanical properties of the resulting silk fiber (SF). The contents of the Cu nanoparticles were 38 times higher in the posterior silk glands and only 2–3 times higher in the SF and in the middle silk glands compared with the controlled groups. Significant changes of the surface morphology, structures, and diameter of the Cu nanoparticle fed SF have been observed, which are attributed to a slight SF protein reconstruction or conformational change in the mixture of silk fibroin and sericin in the silk glands. The resulting Cu-containing SF exhibits good tensile strength of 360 MPa and reaches a strain of 38%, which are 89% and 36% higher than those of the natural SF. This study offers a new green strategy for the easy modification to achieve robust composite SF. [ABSTRACT FROM AUTHOR]

In this study, a high-performance Mg-3Nd-3Gd-0.2Zn-0.5Zr alloy is prepared. The precipitate microstructures of the studied alloy during isothermal aging at 225 °C are characterized by HAADF-STEM observations, and the corresponding mechanical properties are also investigated. It is noted that the evolution of the precipitate microstructure is mainly divided into three stages: the precipitation and growth of β″, the transition from β″ to β 1 , and the ripening of β 1. There are apparent differences in the mechanical properties of alloy in these three stages. At the beginning of aging treatment, due to the precipitation and growth of β″, the yield strength of alloy increases rapidly while the elongation decreases. Afterwards, the transition of precipitates from β″ to β 1 leads to the simultaneous increment in the yield strength and elongation of the alloy. Finally, as the β 1 precipitates ripen, the yield strength of the alloy decreases while its elongation shows a trend of increment owing to the significantly improved dimensions and reduced number density. • Precipitate microstructures and mechanical properties of Mg-3Nd-3Gd-0.2Zn-0.5Zr alloy aged at 225 °C are investigated. • A good combination of strength and elongation is achieved at over-aged Mg-3Nd-3Gd-0.2Zn-0.5Zr alloy • Transition from β″ to β 1 leads to simultaneous increments in the yield strength and elongation. [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]

Rheo-squeeze casting combined with gas bubbling process was proved effective to improve the mechanical properties of AZ91-2 wt%Ca (AZX912) alloy. Increase of gas flow led to improvement of the quality of AZX912 semi-solid slurry and improved ductility of rheo-squeeze casting AZX912 alloy samples. Increase of applied pressure brought refinement in as-cast microstructure and reduction of porosity, as well as continuous improvement in both tensile strength and elongation. Heat treatment at 410 °C promoted dissolution of β-Mg 17 Al 12 phase, morphology modification of Al 2 Ca phase and further increase of both tensile strength and ductility. Compared with conventional squeeze casting, the mechanical properties of rheo-squeeze casting AZX912 alloy were improved by more than 20%. The improvement in mechanical properties was mainly attributed to the grain refinement in microstructure. [ABSTRACT FROM AUTHOR]

Abstract: The present study investigated the effect of cooling rate on the microstructure and mechanical properties of sand casting Mg–10Gd–3Y–0.5Zr alloy with a cooling rate range of 0.7–3.6°C/s. When the cooling rate was increased, the average grain size of α-Mg decreased from 59μm to 39μm, the volume fraction of the second phase increased from 17.6% to 24.5%, and the eutectic compound exhibited continuous network instead of coarsening discontinuous network of plate-shaped microstructure. Energy-dispersive X-ray test results suggested that solute content of RE elements (Gd and Y) was low within the area near the grain boundary of α-Mg with high cooling rate, and solid-solution reaction occurred in the sand casting process. In addition, Vickers hardness (HV) testing indicated that HV increased with the increasing cooling rate, and the volume fraction of second phase (V) played a main role in hardness of the alloys. There was a linear relationship between them, the fitting function was HV=1.25V+63.05, R 2=0.9989. Tensile strength test showed that both of ultimate tensile strength (UTS) and tensile yield strength (TYS) first increased and then decreased with the increasing cooling rate. Based on fracture observations, the types of fracture surface characteristics are correspondingly classified into three modes, transgranular, dimple-like fracture and intergranular fracture with the increasing cooling rate. [Copyright &y& Elsevier]

Abstract: New fluxes containing YCl3 were developed to refine Mg–10Gd–3Y–0.5Zr (GW103K) alloy, with the aim to suppress the loss of expensive heavy rare earth element Y, but also to improve the removal of nonmetallic inclusions. The Y loss, microstructure, mechanical and corrosion properties were investigated. It was found that the loss of Y in the alloy decreased with the increasing of YCl3 in the flux. Thermodynamic calculation indicated that the main reason could be attribute to the decline of the Gibbs free energy, which slows down the reaction rate between MgCl2 and Y. The study demonstrated that the fluxes containing 5wt.% YCl3 additions also exhibited excellent capability of removing nonmetallic inclusions. This greatly improved the mechanical and corrosion properties of GW103K alloy. [Copyright &y& Elsevier]

Abstract: The influence of Zr on the microstructure, mechanical properties and corrosion resistance of Mg–10Gd–3Y (wt.%) magnesium alloy was investigated. The grain size of alloys decreased with Zr content from 0% to 0.93% (wt.%). The addition of Zr greatly improved the ultimate tensile strength (UTS) and the elongation (EL), while slightly improved the tensile yield strength (TYS). The UTS and the EL of the alloy containing 0.93% Zr increased by 125.8MPa and 6.96% compared with base alloy, respectively. The corrosion resistances were found to decrease with Zr content from 0% to 0.42% and then increase from 0.42% to 0.93%. The differences in the sizes and distributions of the Zr-rich particles have significant effects on the corrosion behaviors. The alloy with 0.42% Zr addition revealed the optimum combination of mechanical properties and corrosion resistance. [Copyright &y& Elsevier]

The distinctive mechanical and photothermal properties of Molybdenum sulfide (MoS2) have the potential for improving the functionality and utilization of silk products in various sectors. This paper reports on the preparation of regenerated silk fibroin/molybdenum disulfide (RSF/MoS2) nanoparticles hybrid fiber with different MoS2 nanoparticles contents by wet spinning. The simulated sunlight test indicated that the temperature of 2 wt% RSF/MoS2 nanoparticles hybrid fibers could rise from 20.0 °C to 81.0 °C in 1 min and 98.6 °C in 10 min, exhibiting good thermal stability. It was also demonstrated that fabrics made by manual blending portrayed excellent photothermal properties. The addition of MoS2 nanoparticles could improve the toughness of hybrid fibers, which may be since the mixing of MoS2 nanoparticles hindered the self-assembly of β-sheets in RSF solution in a concentration-dependent manner because RSF/MoS2 nanoparticles hybrid fibers showed a lower β-sheet content, crystallinity, and smaller crystallite size. This study describes a new way of producing high toughness and photothermal properties fibers for multifunctional fibers' applications. [ABSTRACT FROM AUTHOR]

• T 1 and Al 3 (Li, Sc, Zr) phases possess higher thermal stability than that of δ'. • Coarsening/growth kinetics of δ' and T 1 in a cast Al-Li-Cu-X alloy are investigated. • Activation energies for δ' coarsening and T 1 growth are estimated to be 98.7 kJ/mol and 95.6 kJ/mol. High-performance cast Al-Li alloys are highly desirable for a wide range of weight-critical and stiffness-critical applications. This work was undertaken to investigate the microstructural evolution, coarsening kinetics of main precipitates and related mechanical characteristics of a newly-developed cast Al-Li-Cu-Mg-X alloy during aging at 150, 175, 200 and 225 °C. The as-aged alloys studied primarily comprised of δ′ (Al 3 Li), T 1 (Al 2 CuLi), S′ (Al 2 CuMg) and core-shell Al 3 (Li, Sc, Zr) phases. δ′ phases exhibited the relatively lowest thermal stability. The increasing aging temperature led to the greatly enhanced coarsening rate of δ′. It was found that the coarsening of metastable δ′ was a diffusion-controlled process and a linear relationship of cube average particle radius ( R ̅ 3) against aging time t was revealed. The activation energy for the δ′ coarsening was estimated to be ~98.7 kJ/mol, which was somewhat lower than those in wrought Al-Li alloys. Besides, the activation energy for the growth of T 1 plate was measured to be ~95.6 kJ/mol, which was close to that of grain boundary diffusion of Cu in α-Al (~105 kJ/mol), indicating that the growth of T 1 should be governed by the diffusion rate of Cu toward T 1 plates. With the successively increased aging temperature and prolonged aging time, the number density and volume fraction of δ′ particles were significantly reduced, primarily contributing to the significant strength reduction. The relatively best combination of strength and ductility was achieved in the studied alloy aged at 175 °C for 32 h. [ABSTRACT FROM AUTHOR]

This work was undertaken to investigate the specific role of element Gd on the microstructural evolution and mechanical properties of Mg-3Nd-0.2Zn-0.5Zr alloy. It is noticeable that, as the Gd content increases, the average grain size of as-cast alloys is continuously reduced, accompanied by the main secondary phases changing from Mg 12 Nd to Mg 3 Gd. Tensile tests reveal that addition of Gd (1.5–4.5 wt%) could lead to substantial enhancements of alloy strength (25–70 MPa) and an excellent combination of strength and ductility is obtained in the alloy with 4.5 wt% Gd addition (YS = 200 MPa, UTS = 343 MPa, EL = 5.4%). Microstructure characterization indicates that the improved solid-solution strengthening effect originated from increasing Gd additions plays a key role in the significant strength improvements obtained in as-quenched alloys. HAADF-STEM observations suggest that Gd is highly enriched in the dominantly disc-like prismatic β″ phases, leading to the strongly enhanced precipitation kinetics and greatly augmented volume fraction of β″ phase. A quantitative microstructural comparison of peak-aged specimens indicates that the significant strength enhancements should be primarily derived from the denser dispersion of β″ phases with higher aspect radio arising from Gd addition. • Microstructure evolution and mechanical properties of Mg-3Nd-0.2Zn-0.5Zr alloys doped with varied Gd were investigated. • Significant strength enhancements (~70 MPa) is obtained by addition of Gd. • Gd is observed to be incorporated into β″ precipitates and is likely to be substituting for Nd atoms. • Increasing amounts of Gd additions are found to greatly improve the number density and aspect ratio of β″ precipitates. [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]

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]

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 microstructure characterization and mechanical properties of the as-cast and as-extruded Mg- x Li-5Zn-0.5Er (x = 8, 10 and 12 wt%) alloys are investigated. The as-cast Mg- x Li-5Zn-0.5Er alloys contain α -Mg, β -Li, Mg–Zn–Er and Mg–Li–Zn phases. Besides the matrix phase change (α -Mg + β -Li phases or only β -Li phase), the quantity and size of the Mg–Li–Zn phase decrease and the Mg–Zn–Er phase is from discontinuous clubbed dispersion to discrete distribution of irregular masses with the increasing Li content from 8 wt% to 12 wt%. The grains of Mg- x Li-5Zn-0.5Er alloys are all refined after extrusion. A part of the Mg–Zn–Er phase is crushed along the extrusion direction and the Mg–Li–Zn phase which is solid dissolved into matrix during homogenization separates out. The fiber texture of β -Li becomes weaker and the <001> fiber texture appears with the Li addition from 8 wt% to 10 wt%. The strength difference of the as-extruded alloys is primarily attributed to the different precipitated Mg–Li–Zn phase evolution. The highest strength (ultimate tensile strength = 252 MPa) among three as-extruded alloys is obtained in the as-extruded Mg–10Li–5Zn-0.5Er alloy with the most dispersed and fine Mg–Li–Zn particles. • The texture becomes weaker and the <001> texture appears with the Li addition from 8 wt% to 10 wt%. • The evolution of Mg–Li–Zn phase is analyzed in detail. • The highest strength is obtained in the as-extruded Mg–10Li–5Zn-0.5Er alloy with the finest Mg–Li–Zn particles. [ABSTRACT FROM AUTHOR]

In this study, effects of Al and Y contents on microstructural evolutions and mechanical properties of the as‐cast Mg–14Li alloy are investigated. The results show that Mg–14Li–xAl (x = 1, 2, 3 wt%) alloys are characterized by predominantly single β–Li and MgLiAl2 phases. Slight refinement of β–Li grains is obtained with the increasing of Al content. The increased Al addition greatly improves the hardness, ultimate tensile strength, and yield strength of the Mg‐14 base alloy, accompanied by a significant reduction in ductility. Meanwhile, with addition of minor Y (0.5 wt%) addition leads to the introduction of homogeneous distribution of Al2Y particles in the Mg–14Li–3Al alloy, which plays a positive role in the strength enhancement. However, the uneven distribution of apparently coarsed Al2Y particles contributes to a significant reduction in tensile strength as the Y content is increased up to 1 wt%. In the alloy of Mg–14Li–3Al–0.5Y, β–Li phases are dramatically spheroidized after addition of surface‐active element Y. Round‐like Al2Y phases locate along grain boundaries. And considerable secondary crack sources initiate both at grain interiors and along grain boundaries and propagate with a combination of inter‐granular and trans‐granular way. [ABSTRACT FROM AUTHOR]

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]

Abstract This study was undertaken to investigate the influence of Er addition on microstructure and mechanical properties of as-cast Mg-10Li-5Zn alloy. With addition of Er, the grain size of as-cast alloys is greatly reduced, meanwhile, Mg-Zn-Er phase forms and increases gradually and Mg-Li-Zn phase decreases. The Mg-Zn-Er phase is mainly W-phase. The size of W-phase becomes larger with the increase of Er content from 0.5 wt% till 3.5 wt% and W-phase is mainly distributed from in the grain interiors to along the grain boundaries as well. The size, quantity and distribution of W-phase is an important factor that influences the mechanical properties of Mg-10Li-5Zn- x Er alloys. Overmuch coarse W-phase in the grain boundaries is detrimental to strength. The Mg-10Li-5Zn-0.5Er alloy exhibits an optimum combination of tensile properties with the ultimate tensile strength, yield strength and elongation of 198 MPa, 223 MPa and 14.7%. The optimal Er addition in as-cast Mg-10Li-5Zn alloy is ~0.5 wt%. [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]

This study was undertaken to evaluate the effect of heat treatment on the microstructure and mechanical properties of extruded Al–4Cu–1Li–0.4Mg–0.4Ag–0.18Zr alloy. After a three-step homogeneous treatment (480 °C/12 h + 500 °C/12 h + 540 °C/2 h), a Cu-containing secondary phase was found to be dissolved in the α-Al matrix and distributed along the grain boundary in the as-cast state. The effect of the aging temperature, aging time, and amount of pre-deformation on the mechanical properties at ambient temperature was investigated. The results showed that higher aging temperature and longer aging time resulted in higher yield strength (YS), ultimate tensile strength (UTS), and lower elongation (EL). The increase in the amount of pre-deformation significantly promoted YS of the studied alloy, at the cost of a minor decrease in EL. Among the tested samples, the one stretched by 4.5% and aged at 125 °C for 32 h exhibited the highest yield strength. Good mechanical properties, characterized by YS = 629 MPa, UTS = 663 MPa and EL = 9.2% were obtained at ambient temperature. The precipitation behavior and strengthening mechanism were also investigated. The variations in size, number density, and distribution of the T 1 (Al 2 CuLi) and θ′ (Al 2 Cu) phases under different treatment conditions were the main reason for the change in mechanical properties. [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]

In this work, the influences of Mn content on the microstructures and mechanical properties of cast Al-3Li-2Cu-0.2Zr alloy were investigated. The results showed that with the increase of Mn addition, the as-cast grain size was gradually reduced, and the primary Al 20 Cu 2 Mn 3 phase was formed in as-cast higher Mn alloys (0.8Mn and 1.2Mn alloy). The formation of Al 20 Cu 2 Mn 3 dispersoids can restrict the grain growth during solution treatment, but decrease the number density of Cu-rich precipitates during ageing treatment (mainly T 1 -Al 2 CuLi) because they consume the solute Cu available for precipitation. The tensile property results showed that Mn addition had little effect on the yield strength (YS) but a detrimental effect on the ductility of the as-quenched alloys due to the presence of Al 20 Cu 2 Mn 3 dispersoids and/or primary Al 20 Cu 2 Mn 3 phase. With increasing the Mn content, the YS of ageing-treated alloys was continuously decreased, and the highest elongation of 3.5% was obtained in 0.3Mn-bearing alloy after ageing for 32 h at 175 °C. From the comprehensive consideration of ductility and strength, the optimal Mn addition in cast Al-3Li-2Cu-0.2Zr alloy was 0.3 wt.%. [ABSTRACT FROM AUTHOR]

Effects of Sc addition on the microstructure and mechanical properties of cast Al-3Li-1.5Cu-0.15Zr alloy were investigated by microscopy methods and tensile tests. With the addition of 0.15 wt% Sc, the grain size of studied alloy in as-cast state decreased from 120 µm to 30 µm and did not grow obviously after two-step solution treatment (32 h at 500 °C+24 h at 560 °C). After aging at 175 °C for 32 h, the elongation (EL) of Sc-containing alloy reached 5.5%, which increased by 83% compared with Al-3Li-1.5Cu-0.15Zr alloy. The key factors for improvement of comprehensive mechanical properties in Al-3Li-1.5Cu-0.15Zr-0.15Sc alloy could be summarized as follows: grain refining, size reduction of δ’ phases and the precipitation of core/double-shell Al 3 (Li, Sc, Zr) composite particles. [ABSTRACT FROM AUTHOR]

The effects of aging treatment on the high temperature mechanical properties of cast Al–2Li–2Cu-0.5Mg-0.15Sc-0.15Zr-0.05Ti alloy were investigated. Different test temperature (25 °C, 175 °C, 200 °C, 225 °C) and aging time (aging for 8 h, 32 h, 64 h at 175 °C) were designed for comparison. The results showed that at room temperature, the strength of the alloy improved with the prolongation of aging time. When the test temperature increased from 175 °C to 225 °C, the δ′(Al 3 Li)-Precipitation Free Zone (δ′-PFZ) widened from 31.25 nm to 110.83 nm, causing a decrease in strength. In addition, the presence of the dynamic recrystallization at 225 °C resulted in an increase in elongation. As the aging time prolonged from 8 h to 64 h, the high temperature strength of the alloy at 225 °C decreased first and then enhanced. The improvement of alloy strength aged for 64 h was mainly due to the increase of T 1 (Al 2 CuLi), S′(Al 2 CuMg) phases and the decrease of δ′(Al 3 Li) phases. The alloy aged for 64 h exhibiting excellent high-temperature performance at 225 °C, which the yield strength reached 302 MPa, the tensile strength reached 312 MPa and the elongation reached 4.4%. The results indicated that δ′-PFZ widening, precipitation strengthening and dynamic recrystallization were the main factors which influenced the high temperature mechanical properties of Al–Li–Cu alloy. [ABSTRACT FROM AUTHOR]

[Display omitted] • The prepared Mg-Li matrix composite achieves a combination of high Young's modulus (60 GPa) and ductility. • Precipitations on the TiB 2 surface are observed and identified for the first time in Mg-Li matrix composites. • The precipitations on the TiB 2 ′s surface improves ductility by absorbing stress and reducing dislocations. The development and application of lightweight materials boasting an elevated elastic modulus have emerged as a focal point in the realm of materials research. A novel Mg-8Li-3Al-2Zn-0.5Y (wt.%, LAZ832) matrix composite reinforced with ex situ micron-sized TiB 2 particles was introduced in this work. The uniformly distributed TiB 2 particles were achieved through ball milling pretreatment and subsequent hot extrusion. A comprehensive analysis of the composite's microstructure and mechanical properties was conducted. Mg-Li-Al-Zn precipitation regions formed at the TiB 2 interface was identified firstly. This softening region significantly enhanced the ductility of the composite by reducing the dislocation density and stress concentration around the TiB 2 particles. The ductility and the elastic modulus of the as-extruded composite increased significantly with ideal ultimate tensile strength (UTS = 270 MPa). This work highlights an ultra-light Mg-Li matrix composite attaining high modulus (60 GPa) and notable elongation to fracture (19.1 %), demonstrating significant potential for future applications. [ABSTRACT FROM AUTHOR]

Abstract: In order to improve the purifying efficiency of RJ6 flux, 5wt.% YCl3 additions were introduced into the flux to refine Mg–10Gd–3Y–0.5Zr (GW103K) alloy. The results show that the RJ6 flux containing 5wt.% YCl3 additions exhibits excellent adsorption ability to nonmetallic inclusions. Thermodynamic analysis indicates that the main reason could be attributed to the decrease of the surface tension of the flux. Moreover, the mechanical, corrosion and fluidity properties of the alloy were investigated. It was found that these properties were improved to a certain degree due to the removal of nonmetallic inclusions in the alloy. [Copyright &y& Elsevier]

In this work, solution and low-temperature (50–125 °C) aging treatment is utilized to develop a novel Mg-Li alloy with an excellent combination of strength and ductility. After optimizing the solution time, effects of aging treatment on microstructure and mechanical properties of the Mg-8Li-3Al-2Zn-0.5Y alloy were investigated. The highest strength is obtained after solution heat treatment at 350 °C for 4 h, accompanied with relatively low ductility. The following low-temperature aging treatment is used to balance the strength and ductility. With the increase of aging temperature, the ductility of the alloy was improved, accompanied by continued decrease in strength. The formation and aggregation of Al-Li phase during aging treatment is the major factor that influences the mechanical properties of the aged alloys. The reduced solid solution strengthening of Al and the aggregation of Al-Li phase are detrimental to strength. The evolution of Al-Li phase during aging treatment at different temperature is analyzed in detail. Through promoting the precipitation and preventing the aggregation of Al-Li phase by optimizing aging temperature, well-designed low-temperature aging treatment (75 °C × 4 h) results in favorable microstructural evolution and optimum combination of strength (yield strength = 216 MPa, ultimate tensile strength = 276 MPa) and ductility (elongation = 11.1%). • The reduced solid solution strengthening of Al and the aggregation of Al-Li phase are detrimental to strength. • The evolution of Al-Li phase during aging treatment at different temperature is analyzed in detail. • Well-designed aging treatment results in optimum combination of strength and ductility. [ABSTRACT FROM AUTHOR]

This study was undertaken to evaluate the effect of extrusion ratio on the microstructure and mechanical properties of Mg–8Li–3Al–2Zn–0.5Y (wt%) alloy, which was prepared by casting and then deformed by hot extrusion at 200 ℃ with four different ratios of 4:1, 9:1, 16:1 and 25:1, respectively. It was identified that the as-cast Mg–8Li–3Al–2Zn–0.5Y alloy is composed of α -Mg, β -Li, AlLi, MgLi 2 Al and Al 2 Y phases. After hot extrusion with all four ratios, the microstructure was significantly refined. The mechanical properties of Mg–8Li–3Al–2Zn–0.5Y alloy at room temperature were improved, mainly caused by grain refinement and precipitation strengthening. As the extrusion ratio increases from 4 to 25, the grains of the alloy become elongated and refined, and the tensile properties first increase and then decline. Among all the tested alloys, the alloy with the extrusion ratio of 16 exhibits the highest yield strength, ultimate tensile strength and elongation of 214 MPa, 243 MPa and 41%. In addition, the fracture behavior and strengthening mechanism of the studied alloys were also investigated systematically. [ABSTRACT FROM AUTHOR]

In this study, the microstructure evolution and mechanical properties of as-cast Mg–8Li–3Al–2Zn–0.5Y alloy during solid solution treatment from 300 °C to 450 °C were firstly investigated, and then the effect of Y content (from 0.5 wt% to 1.5 wt%) on the age softening of solid solution treated Mg–8Li–3Al–2Zn alloy was also analyzed. The results show that the as-cast Mg–8Li–3Al–2Zn–0.5Y alloy mainly consists of α -Mg, β -Li, Al 2 Y and AlLi phases. With the increase of solid solution temperature from 300 °C to 450 °C for as-cast Mg–8Li–3Al–2Zn–0.5Y alloy, the AlLi phase is decomposed and the atoms of Al and Li dissolve into the matrix gradually. The hardness, yield strength and ultimate tensile strength of the tested alloy are increased dramatically; however, the ductility is relatively decreased. Meanwhile, the room temperature aging treated Mg–8Li–3Al–2Zn–0.5Y has age hardening during initial time, and the addition of Y is helpful to the thermal stability of Mg–8Li–3Al–2Zn alloy. In addition, the fracture behavior and strengthening mechanism of the studied alloys were also investigated systematically. [ABSTRACT FROM AUTHOR]

In this study, effect of Y on microstructure and mechanical properties of as-cast Mg–8Li–3Al–2Zn alloy was investigated. The results show that microstructure of the Mg–8Li–3Al–2Zn alloy mainly consists of α -Mg, β -Li, AlLi and MgLiAl 2 phases. With addition of Y, the Al 2 Y compound forms and increases gradually, the AlLi phase decreases and the β -Li phase increases, meanwhile, the microstructure is significantly refined and equiaxed. The addition of 1 wt% Y produces the smallest grain size. Mg–8Li–3Al–2Zn–0.5Y alloy exhibits an optimum combination of tensile properties with the ultimate tensile strength, yield strength and elongation of 153.0 MPa, 218.5 MPa and 16.9%, which are improved by about 6.4%, 13.2% and 13.4% compared with those of Mg–8Li–3Al–2Zn alloy (143.8 MPa, 193.0 MPa and 14.9%), respectively. The mechanisms of improvement are related to grain refinement and second phase strengthening. [ABSTRACT FROM AUTHOR]

The effect of Al additions on grain refinement and mechanical properties of Mg–Sm alloys has been investigated. The addition of 3 wt.% Al led to significant grain refinement of Mg– x Sm ( x = 4, 6 and 8 wt.%) alloys due to the formation of Al 2 Sm particles which acted as active nucleant particles for the Mg matrix. An orientation relationship ( 1 ¯ 1 1 ) Al 2 S m / / ( 0 0 0 2 ) Mg , [ 1 ¯ 2 ¯ 1 ] Al 2 Sm / / [ 1 1 2 ¯ 0 ] Mg , [ 0 1 ¯ 1 ] Al 2 Sm / / [ 0 1 1 ¯ 0 ] Mg was reproducibly observed between α-Mg and Al 2 Sm. Furthermore, the Mg–4Sm alloy refined by Al additions had higher ultimate tensile strength and elongation than that refined by Zr which is considered as the most potent grain refiner for Mg alloys. [ABSTRACT FROM AUTHOR]

Abstract: The effect of additions of 0.5–1wt% Al on grain refinement, heat treatment and mechanical properties of Mg–10Gd–3Y (wt%) alloy has been investigated. The additions of 0.6–1wt% Al showed a dramatic grain refinement effect, which is associated with the formation of the Al2(Gd0.5Y0.5) particles that act as nucleants for α-Mg grains. Compared to the Zr refined counterpart, the Al refined alloy needed to be solution treated at a higher temperature to dissolve the majority of the intermetallic particles. Subsequent ageing at low temperatures led to pronounced precipitation hardening and consequently a large improvement in strength. In the peak-aged condition, the strength of the Al refined alloy is comparable to that of the Zr refined counterpart. [Copyright &y& Elsevier]