Search

It is well known that the development of lightweight alloys with improved comprehensive performance and application value are the future development directions for the ultra-high-strength 7xxx series Al-Zn-Mg-Cu alloys used in the aircraft field. As the lightest metal element in nature, lithium (Li) has outstanding advantages in reducing the density and increasing the elastic modulus in aluminum alloys, so Al-Zn-Mg-Cu alloys containing Li have gained widespread attention. Furthermore, since the Al-Zn-Mg-Cu alloy is usually strengthened by aging treatment, it is crucial to understand how Li addition affects its aging precipitation process. As such, in this article, the effects and mechanism of Li on the aging precipitation behavior and the impact of Li content on the aging precipitation phase of Al-Zn-Mg-Cu alloys are briefly reviewed, and the influence of Li on the service properties, including mechanical properties, wear resistance, and fatigue resistance, of Al-Zn-Mg-Cu alloys are explained. In addition, the corresponding development prospects and challenges of the Al-Zn-Mg-Cu-Li alloy are also proposed. This review is helpful to further understand the role of Li in Al-Zn-Mg-Cu alloys and provides a reference for the development of high-strength aluminum alloys containing Li with good comprehensive properties. [ABSTRACT FROM AUTHOR]

Electrically actuated movement of liquid metals is quite promising in mechanical engineering and applied physics. However, little work has so far been performed on the effect of current polarity on the actuation of the eutectic gallium–indium (EGaIn) alloy moving on metal substrates. In this work, the spreading of EGaIn on copper (Cu) substrate under different direct-current (DC) polarities in the 0.5 mol/L NaOH solution was investigated, and the underlying mechanisms were addressed. When the Cu substrate was connected to cathode, the wetting was essentially attributed to the reduction in the oxidized surface of the Cu substrate; whereas, under the opposite polarity, the spreading was related to the tension gradient along the EGaIn–solution interface, which induced Marangoni flow, despite the fact that the EGaIn–Cu system was non-wetting in this case. Unlabelled Image • Application of DC drives the spreading of EGaIn on Cu substrate. • The spreading behavior varies greatly with DC polarity. • Spreading under wetting condition is primarily attributed to deoxidation of Cu surface. • Spreading under non-wetting condition is mainly due to Marangoni flow. [ABSTRACT FROM AUTHOR]

Abstract The present work revealed a potential to control the static recrystallization kinetics through regulating the feature of pre-existing Mg 17 Al 12 particles in Mg-Al-Zn alloys. The AZ31 (Mg-3Al-1Zn) with rarely dispersoids exhibits the fastest recrystallization rate, while the AZ61 (Mg-6Al-1Zn) with only fine particles (∼100 nm) recrystallizes slower than AZ91 (Mg-9Al-1Zn) containing Mg 17 Al 12 precipitates with scattered size distribution (ranging from less than 100 nm to above 0.6 μm). Especially, we found that coarse Mg 17 Al 12 particles in AZ91 are easier to trigger particle stimulated nucleation (PSN) at 275 °C than 175 °C, which compensates the strong recrystallization inhibition of fine dispersoids, leading to the recrystallization dramatically transforms from retarded to accelerated. Graphical abstract Image 1 Highlights • The precipitate feature notably affects the kinetics of static recrystallization. • Recrystallization of alloys with mixed particle size is sensitive to temperature. • Coarse particles in Mg-9Al-1Zn accelerate recrystallization at high temperature. • The study shows an efficient route to control the static recrystallization process. [ABSTRACT FROM AUTHOR]

Abstract Al–Si–Mg alloys manipulated by in-situ synthesized nanoparticles have been prepared by casting method in this work. The addition of different contents of refiners promoted the obvious grain refinement of the Al–Si–Mg alloys. It was found that 0.10 wt% refiners addition caused a significant and efficient refinement on α-Al (from 1675 µm to 199 µm) and Mg 2 Si in the inoculated Al–Si–Mg alloys. The morphology of the eutectic Si in the inoculated Al–Si–Mg alloys transformed from needle-like structure to a fibrous one, and the mean size sharply decreased (from 26.56 µm to 11.89 µm) and increased a little with the increase of FeBSi amorphous refiners content. Tensile property tests showed that both strength and ductility of the alloys were improved by the addition of FeBSi amorphous refiners. The yield strength, tensile strength, fracture strain and elongation of the alloy inoculated with 0.10 wt% FeBSi amorphous refiners for 20 min were 226 MPa, 343 MPa, 18.4% and 16.7%, compared to those of the uninoculated alloy (170 MPa, 289 MPa, 13.7% and 12.2%), respectively. It was found that the Fe 2 B and Fe 3 Si nano-sized particles which were crystallized from FeBSi amorphous refiner contributed to the grain refinement of α-Al, resulting in higher strength. Moreover, grain refinement shortened the atomic diffusion distance and refines Mg 2 Si. The grain refinement and spheroidization of eutectic Si enhance uniform deformation during tension, and reduce the possibility of crack initiation and expansion, thus improving the plasticity. Graphical abstract fx1 Highlights • The inoculated Al–7Si–0.3Mg alloy appeared as 199 µm fine grains. • The inoculated alloy reached 226 MPa, 343 MPa, 18.4%(δ) and 16.7%(ε f). • This work achieved the refinement of α-Al and Mg 2 Si and the spheroidization of eutectic Si. • The Fe 2 B, Fe 3 Si had better lattice mismatch with α-Al and eutectic Si. [ABSTRACT FROM AUTHOR]

The overall microstructure-manipulated Al-13Si-5Cu-0.6 Mg alloy was successfully fabricated via introducing 0.1 wt% Zr 55 Cu 30 Al 10 Ni 5 amorphous alloy manipulator with short time of 60 s, to determine its suitability for applications at room and higher temperatures. The microstructure manipulation mechanism, mechanical properties and strengthening mechanism in manipulated Al-13Si-5Cu-0.6 Mg alloy were discussed. The Zr 55 Cu 30 Al 10 Ni 5 amorphous alloy manipulator provides more nucleation sites in the formation of primary Si, Al Si eutectic and Al 2 Cu. As a result, the optimal microstructure is composed of finer α-Al grains, Al 2 Cu and more rounded primary and eutectic Si, with sizes decreased to ∼52%, 13%, 73% and 42%, respectively. The yield strength, tensile strength, elongation and fracture strain of manipulated Al-13Si-5Cu-0.6 Mg alloy are improved by 22.9%, 16.8%, 58.2% and 47.7% at room temperature than those of the unmanipulated Al-13Si-5Cu-0.6 Mg alloy, respectively. The improved tensile properties at room temperature are attributed to the significant strengthening effect of smaller precipitates and grain refinement while the excellent plasticity is derived from finer α-Al grain, round-corner primary Si and eutectic Si spheroidization. The yield strength and tensile strength are increased by 28.1% and 15.3% at 250 °C, and 28.3% and 10.8% at 300 °C, respectively. The strengthening mechanism at high temperature is mainly the second phase strengthening and the effect of finer eutectic Si on the pinning grain boundary. The overall microstructure manipulation in this work provides better comprehensive mechanical properties and a practicable method to fabricate the Al-Si-Cu-Mg alloy with superior strength and ductility, especially for die-casting alloy with short-time and high-efficiency. [Display omitted] • Fully microstructure-manipulated alloy was made via adding trace nanoparticles. • Nanosized ZrCu(B2) and Zr 2 Cu have ideal lattice mismatch with Si, α-Al and Al 2 Cu. • The sizes of primary Si, α-Al, eutectic Si and Al 2 Cu decreased simultaneously. • The tensile strength and elongation of manipulated alloy are greatly improved. [ABSTRACT FROM AUTHOR]

Insufficient performance, especially at high temperatures, limits the extensive application of cast Al–Cu alloys. This study proposes a novel method of direct reaction synthesis (DRS) for the simultaneous synthesis and dispersion of hybrid-sized in situ TiC–TiB 2 particles in the melt to prepare a trace-particle-reinforced high-performance cast Al–Cu 5.5 –Mn 0.45 –Ti 0.3 –V 0.3 –Cr 0.2 –Zr 0.14 –B 0.04 alloy. The particulate-reinforced alloy achieved strength–ductility synergetic enhancement at room and high temperatures. In comparison to the Al–Cu matrix alloy, the yield strength of 0.7 wt% (TiC–TiB 2)/Al–Cu alloy at 298 K (529 MPa), 493 K (214 MPa), and 533 K (183 MPa) had an increase of 28%, 18% and 35%, meanwhile their elongation increased by 4%, 50% and 62%, respectively. The yield strength enhancement primarily benefited from the thermal mismatch between the particles and matrix, and Orowan strengthening. The strength–ductility performance improvement is due to the optimization of the microstructure: significantly refined α-Al grains with smaller and more dispersed θʹ precipitates. Further, the improvement mechanism of the microstructure is due to the action of the nanoparticles on the heterogeneous nucleation stimulation and dendrite growth inhibition of α-Al during the solidification process. Meanwhile, the segregation of the Cu atoms was inhibited by the particles. The precipitation was significantly promoted because of more uniformly distributed Cu atoms, and more defects induced by particles improved diffusion of the Cu atoms the number and density of the precipitation sites. The results of this study provide an economical and accessible synthesis strategy for industrial manufacturing. [ABSTRACT FROM AUTHOR]

We report a new rolling route combining one pass of hard-plate rolling and two passes of conventional rolling. This route is efficient in achieving near-spherical Mg 17 Al 12 phase (~0.5 µm) and uniform fine-grained structure (~3 µm) featuring a weakened texture in AZ91-0.4Sn plates after a total thickness reduction of ~86.4% via 3 rolling passes. Moreover, the processed alloy exhibited superplasticity-like fracture strain of ~96% at 200 °C, owing to fine α-Mg grains distributed with a high volume fraction of Mg 17 Al 12 . This new route significantly reduces rolling passes and hence has a great potential for industrial production. [ABSTRACT FROM AUTHOR]

Adding alloying elements to increase precipitation is a common method to strengthen aluminum (Al) alloys, but an excessively high alloying element content causes segregation and a reduction in plasticity. In this work, the tradeoff between alloying element content and segregation was explored along with the simultaneous increase in precipitation and dislocation density under the action of trace TiB 2 +TiC particles with the aim of giving a full play to the strengthening effect of dislocation and precipitation and maximizing the strength and toughness of the alloy. The cast Al–Zn–Mg–Cu alloys contained various alloying elements (Zn, Mg), and the alloys were reinforced with 0.5 wt% TiB 2 +TiC particles via in-situ reaction in the Al melt. The TiB 2 +TiC particles blocked the diffusion of the alloying elements and inhibited segregation, promoting solution of alloying elements and yielding dispersed and finer precipitates after solution and aging. Meanwhile, owing to the difference in the thermal expansion coefficients of the matrix and particles, the dislocation density of the alloy doubled. Therefore, the yield strength, elongation, and the product of the tensile strength and elongation of the Al-6.60Zn-3.15Mg-1.60Cu alloy with particles reinforcement were 562 MPa, 4.5%, and 3163 MPa·%, respectively, representing increases of 31.6%, 108.9%, and 186.0%, respectively, compared with the cast 7075 alloy. This study is significant for the successful preparation of high-strength and high-toughness cast aluminum alloys with high alloying-element content. [ABSTRACT FROM AUTHOR]

It is challenging to concurrently control the microstructure evolutions after undergoing casting, sheet forming and welding. This study successfully addressed this challenge via trace TiC–TiB 2 nanoparticles in the amelioration of solidification-rolling-welding microstructural evolution. Nanoparticles refined the solidified microstructures and significantly increased the net driving force for recrystallization, promoting the precipitation of nanoscale Guinier–Preston zones and β'' phases. The coarsening of the fusion and heat-affected zones was also effectively suppressed. The yield strength (YS) and ultimate tensile strength (UTS) of the rolled plates were enhanced by 31.3% and 16.3%, respectively, without significantly sacrificing ductility. Additionally, the YS and UTS of the as-welded welding joints were enhanced by 30.2% and 7.8%, respectively. The amelioration mechanism of TiC–TiB 2 throughout the microstructural evolution and strengthening process was systematically investigated. This study provides a typical model for the complete amelioration of microstructural evolution in aluminum alloys under multiple processing conditions. • The nucleation of solidified phases is promoted, and their growth is hindered. • Recrystallization and formation of coherent nanoscale precipitates are promoted. • Coarsening of fusion zone and heat affected zone is suppressed. • Building better microstructure configuration for improved properties. [ABSTRACT FROM AUTHOR]

Primary Mg2Si with a truncated octahedral morphology and size over a range of 8–15 μm were prepared by simultaneously adding Ca and Sb into the Al–Mg–Si melt. It is revealed for the first time that CaSb2 can act as the nucleus of primary Mg2Si during solidification, which changes the morphology and refines the size of primary Mg2Si significantly. It is useful for improving the mechanical properties of the Al–Mg–Si alloy. The skeleton-type growth processes of truncated octahedral primary Mg2Si crystals were identified by observation of the three-dimensional (3-D) morphologies of the crystals extracted from the Al–Mg–Si alloy. The content of Ca and Sb plays an important role in determining the morphologies of primary Mg2Si, which can be transformed from coarse dendrites to defective truncated octahedra and finally to the coexistence of perfect truncated octahedra and flat truncated octahedra with increasing the content from 0 to 0.2 and then to 0.5 wt%. Our study provided a one-step less-cost method to change the morphologies and sizes of primary Mg2Si, which is important to tailor new light-weight alloys with high strength and toughness. [ABSTRACT FROM AUTHOR]

Wetting of hot-pressed polycrystalline WC substrates by a Zr55Cu30Al10Ni5 bulk metallic glass (BMG)-forming alloy was investigated at 1133–1253 K in a high vacuum using a modified sessile drop method. The alloy melt spread rapidly on the WC surface, reaching no more than 30° within 3 s, and then slowly (at T < 1213 K) or even remained steady (at T ≥ 1213 K) in the subsequent isothermal dwelling stage. The final equilibrium contact angles were between 11° and 20°, slightly increasing with rising temperature and thus presenting an appreciably anomalous temperature-dependent behavior. The reaction between WC and the Zr-base melt was moderate, slightly enhancing with increasing temperature, and yielded W, ZrC and W5Zr3 at the interface. The wetting, in principle, was driven by the formation of a precursor film in front of the triple line as a result of the adsorption of active atoms (primarily Zr) rather than by the interfacial reaction. From the viewpoint of the wettability and reactivity, WC is a good reinforcement for the preparation of the Zr-base BMG matrix composites. [ABSTRACT FROM AUTHOR]

Abstract: After combined additions of Sr and Sb, most primary Mg2Si crystals in Mg–3.5Si–1Al and Mg–5Si–1Al alloys transformed from equiaxed-dendritic shapes to octahedral morphologies; while eutectic phases also changed from Chinese script to short rod-shapes. The mechanisms of complex modification of Sr and Sb were attributed to the heterogeneous nucleation of primary Mg2Si on Sr11Sb10 nucleus, together with change in growth manners caused by incorporation of Sb in Mg2Si crystals. [Copyright &y& Elsevier]

Abstract: As-cast Mg–3Al–3Sn (AT33) alloy exhibits strong strain hardening ability, which is illustrated by the very high H c and n values. Decrease in generalized stacking fault (GSF) energies in AT33 alloys by Al and Sn additions facilitates the production of dislocations and activation of deformation twins, causing the accumulation of dislocations at twin boundaries, resulting in a high dislocation density in deformed alloys during tension deformation, which thereby mainly accounts for the strong strain hardening ability. [Copyright &y& Elsevier]

Abstract: The wetting and evaporation behaviors of Mg–Al alloys over a full composition range on partially oxidized polycrystalline α-SiC substrates were studied in a flowing Ar atmosphere using an improved sessile drop method. The time dependence of the changes in contact angle and drop geometry was monitored and representative wetting stages were identified. The initial contact angles at 1173K were 100° for pure Al and 76° for pure Mg, with the maximum value of 106° for the 7.6mol.% Mg–Al alloy. The interfacial reaction and the evaporation of Mg led to the decrease in the apparent contact angle in the spreading stage and their respective contribution was evaluated. After the pinning of the triple line, the decrease in the contact angle resulted from the diminishing drop volume as a consequence of the Mg evaporation. The effects of Mg concentration on the wetting and evaporation behaviors were discussed. A mechanism for the time-dependent diminishing drop volume was proposed in light of the competition between the Mg evaporation and its diffusion from the drop bulk to the surface. Finally, the interfacial reaction was analyzed based on thermodynamic considerations. [Copyright &y& Elsevier]

Abstract: The modification of Mg2Si in Mg–5Si alloys with KBF4 was investigated in detail. With the increase of KBF4 content, the alloys exhibited sub-modified and fully modified microstructures, but no over-modified microstructure was found. In the fully modified alloys, most of the primary Mg2Si particles exhibited the morphology of octahedrons. It is believed that B which came from the decomposition of KBF4 effectively confined the growth of primary Mg2Si to the octahedron morphology. [Copyright &y& Elsevier]

A new design method of Al-Si-Mg alloy manipulated by in situ nanosized crystals was proposed. Starting from source design of the microstructure manipulation agent with a high crystallographic matching relationship with the α-Al, eutectic Si and Mg 2 Si phases in Al-Si-Mg alloy, the interatomic misfit (f r) between NiTi(B2) and α-Al or Mg 2 Si is 5.0% or 5.3%, respectively, and that between NiTi(B2) and Si is 9.9%, corresponding to good crystallographic matching. Based on calculations, in situ nanosized crystals could be considered as heterogeneous nucleation sites of α-Al, eutectic Si and Mg 2 Si, thus, uniformly fine α-Al grains, near-spherical eutectic Si and fine precipitated Mg 2 Si were obtained. The solidification behavior analysis also highly corresponded to the E2EM calculations. In the alloy manipulated by 0.05 wt% NiNbTi manipulation agent, the average sizes of α-Al, eutectic Si and Mg 2 Si were greatly decreased by nearly 8, 2 and 20 times, respectively, thus achieving comprehensive multiscale manipulation of the microstructure of the alloy in one step. Specially, the huge energy stemmed from the B2 to B19' phase transformation will generate a large number of crystal defects, which provides nucleation sites and driving force for the formation of Mg 2 Si and greatly refines the Mg 2 Si.Moreover, the yield stress, tensile stress and fracture strain of the manipulated alloy were simultaneously improved by 34.1%, 20.4% and 35.0%, respectively. The excellent strength and plasticity could be ascribed to grain-refinement strengthening, Orowan strengthening and eutectic Si refinement and spheroidization, which reduced the stress concentration during deformation. The comprehensive microstructure manipulation of Al-Si-Mg alloy using nanosized crystals formed by in situ physical crystallization, especially the manipulation of the precipitated phase, is an innovative work that not only avoids the "poisoning" effect between multiple manipulation agents but also realizes comprehensive manipulation of the overall microstructure, consequently broadening further industrial applications. • The low fr shows good mismatch between Al, Si, Mg 2 Si and NiTi. • The new method achieves multiscale manipulation of the alloy in one step. • The mean sizes of α-Al, eutectic Si and Mg 2 Si were decreased by nearly 8, 2 and 20 times. • The yield strength and plasticity were simultaneously improved by 34.1% and 35.0%. [ABSTRACT FROM AUTHOR]

• Al matrix composites reinforced with different nanoparticles were investigated. • The corrosion behaviors of the composites were related to the passive film. • TiC p were beneficial for improving the corrosion behavior, but TiB 2p were not. • TiC p reduced the grain boundary phases, improving the corrosion behavior. • TiB 2p at grain boundaries form more corrosion channels, increasing the corrosion rate. Nanosized TiC and TiB 2 particles (TiC p , TiB 2p) can increase the mechanical properties of Al alloys. However, their effects on the corrosion performance of Al alloys are relatively less understood. The corrosion behavior of Al-Mg-Si alloys is improved by adding TiC p and worsened by adding TiB 2p. These changes result from i. TiC p refining the grain structure by acting as nucleants and reducing the number of grain boundary phases and ii. TiB 2p segregating at grain boundaries and accelerating the corrosion. This provides a selection criterion that can be utilized for reinforcement nanoparticles for wrought Al alloys that are applied in corrosive environments. [ABSTRACT FROM AUTHOR]

Al Cu alloys inoculated by in-situ nano-sized particles crystallized from Ni-Nb-Ti amorphous alloys were prepared by casting method in this work. Different compositions of Ni-Nb-Ti amorphous alloys significantly enhanced heterogeneous nucleation for α-Al and promoted obvious grain refinement of the Al Cu alloys. It was found that 0.05 wt% Ni-Nb-Ti amorphous alloys addition caused a significant and efficient refinement on α-Al (from 200 μm to 39 μm) and θ′ phase (from 146.4 nm to 37.6 nm). The strength and ductility of the inoculated alloy were improved significantly at high temperature. The tensile strength and fracture strain of the alloy inoculated by 0.05 wt% Ni-Nb-Ti amorphous alloy for 20 min at 533 K under the strain rates of 10−1 s−1 were increased by 32.63% and 90.35% respectively, compared to those of the uninoculated alloy. The nano-sized NiTi particles contributed to the grain refinement of α-Al, and grain refinement shortened the solute atomic diffusion distance and refined θ′ phase during heat treatment, resulting in higher strength and plasticity at high temperature. The model developed for this new type Al Cu alloy is found to be efficient in predicting the stress at 453 K–533 K under the strain rates of 10−4 s−1 to 10−1 s−1. • In-situ nano-sized NiTi can serve as efficient heterogeneous nuclei of α-Al. • Inoculation caused a significant refinement on α-Al and precipitation θ′ phase. • The tensile strength and fracture strain were increased by 32.63% and 90.35% respectively at 533 K with 10−1 s−1. • The enhanced tensile property was due to the finer θ′ phase which impeded dislocation motion. • A stress prediction model was presented at 453 K–533 K under the strain rates of 10−4 s−1 to 10−1 s−1. [ABSTRACT FROM AUTHOR]

At high temperatures, the weakened strength and decreased ductility of Al alloys limit their industrial applications. (TiB 2 –TiC)/Al–Cu–Mg–Si composites were synthesized by adding in situ dual-phased and bimodal-sized (TiB 2 –TiC)/Al master alloys to molten Al–Cu–Mg–Si alloys. The addition of minor amounts of TiB 2 and TiC particles (0.05 and 0.1 wt%, respectively) effectively refined the α-Al grains and θ′ and Q′ precipitates and increased the elevated-temperature strength and uniform elongation of the Al–Cu–Mg–Si alloys. The 0.1 wt% (TiB 2 –TiC)/Al–Cu–Mg–Si composite showed the best yield strength (279 MPa), ultimate tensile strength (366 MPa), and uniform elongation (10.6%) at 493 K, with enhancements of 9.4%, 15.1%, and 24.7% compared to the Al–Cu–Mg–Si matrix alloy (255 MPa, 318 MPa, and 8.5%). The simultaneous increases in the elevated temperature strength and ductility of the composites were attributed to the strengthening effects of the bimodal-sized TiB 2 and TiC particles, θ′ and Q′ precipitation strengthening, and the refined partial recrystallization microstructure. [ABSTRACT FROM AUTHOR]