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The application of 6005A aluminum alloy in transportation is increasing, which puts forward higher requirements for the fatigue performance of welding process. In this study, friction stir welding (FSW) enhanced treatment was applied on the traditional metal inert gas (MIG) weld. The results show that the fatigue life of FSW plate is three times higher than that of original MIG welded plate at 140 MPa stress level. Under 107 cycles, the fatigue life limit was increased by 16 MPa compared with as-received MIG plate. The main reason of FSW leading to the increasing fatigue life are the reduction of porosity to reduce crack initiation and grain refinement to delay crack propagation.

Grains with size of 4.5–20.5 μm were studied for their corrosion behavior and electrochemical performance in a Mg-3Al-5Pb-1Ga-Y sacrificial anode using immersion testing, electrochemical measurements and microstructure analysis. The results show that fine-grained microstructure has higher chemical activity and more negative discharge potentials than coarse-grained samples. The sample with the smallest average grain size of 4.5 μm exhibits corrosion current density of 7.473 × 10−5 A/cm2, and work potentials of −1.721 V at current density of 10 mA/cm2. The density of grain boundaries and LAGBs increases with grain refinement, which leads to higher rates of dissolution and diffusion for the atoms. The secondary phases promote the occurrence of corrosion and improve the chemical activity of alloy due to their higher potential than the substrate. Higher corrosion rate and discharge activity are directly attributed to the higher density of grain boundaries and LAGBs, as well as the secondary phase.

We herein report our investigation into the influence of cold-rolling on the recrystallization texture of the Zr-1Sn-0.3Nb-0.3Fe-0.1Cr alloy during annealing. The as-received plates were cold-rolled at 25 °C with different reductions of 6, 10, 14, 18, 30, 40, 50 and 70%. All cold-rolled sheets were annealed at 580 °C for 3 h, while 14 and 30% cold-rolled samples were also annealed at 580 °C for 12 h. The microstructures of the annealed samples were characterized by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). Abnormal grains growth with about 23 μm in size appeared in the samples with 14% reduction and annealed at 580 °C for 3 h, which corresponded to the critical degree of alloy deformation. The texture of the 14% cold-rolled sheet was typical rolling texture //ND, after annealing, cold rolling texture was still retained. While the texture of the 30% cold-rolled sheet was 2 ¯ 0> parallel to the rolling direction ( 2 ¯ 0>//RD), which changed to the recrystallization texture //ND, 1 ¯ 0>//RD and 2 ¯ 0>//RD characteristics after annealing. The loading direction is along the rolling direction (RD), the slip system and the Schmid factor are analyzed to more deeply understand and evaluate the plasticity of further rolling or punching. When the loading direction is along the rolling direction (RD), the predominant slip systems of annealed 14% reduction samples was prismatic and pyramidal plane system, and the annealed 30% reduction samples were prismatic with a pyramidal plane system. This implies that the use of 30% cold-rolled reduction and annealing at 580 °C for 12 h imparts a superior plasticity to the alloy, which may allow its application in future deformations, such as rolling or punching.

The objective of the present study is to investigate the high-cycle fatigue (HCF) and fatigue crack propagation (FCP) characteristic in relation to the microstructure in the 5083-O aluminum alloy. The HCF strengths of the 5083-O Al alloy in parallel to rolling direction (PD) and vertical to rolling direction (VD) specimens are 164 MPa and 165 MPa, respectively, However, the FCP resistance of the specimens reveals evident anisotropy. The FCP resistance of the PD specimen is less than that of the VD specimen, which is predominantly caused by the main crack expanding along the chain-shaped coarse inclusions in PD specimen. These chain-shaped coarse inclusions, particularly, Fe/Mn containing particles with secondary microcracks, might accelerate FCP rate and decrease FCP resistance.

Microstructure characteristics and restoration mechanism were studied in a near-β Ti-5Al-5Mo-5V-1Cr-1Fe alloy after the single- and multi-pass compression at 800 °C (below the β-transus) and 950 °C (above the β-transus) with the strain rate of 5s−1, 30s−1 and 50s−1. The results showed that the restoration mechanism of the alloy in β phase during the compression in β phase region was dynamic recovery (DRV) while DRV and dynamic recrystallization (DRX) occurred during the compression in α+β region. The involvement of α phase in α+β phase region promoted the DRX of β phase. Multi-pass compression at 800 °C has greater impact on the microstructure evolution of the alloy than strain rate change. The frequency of fine β grains/subgrains (grain size of 0∼5 μm) in the 800 °C/5-pass compressed sample was significantly higher than that in the 800 °C/1-pass compressed one. 5-pass compression at 800 °C results in enhanced fragmented α, which promoted the formation of finer β subgrains by introducing the heterogeneous deformation. This deformation route provides an effective way to obtain fine subgrain structure for quick forging parts of this alloy.

A spheroidal Al3(Zr,Sc) precipitate with a double-shell structure, comprising a Sc-enriched core enveloped by a Zr-enriched inner shell and a Sc-enriched outer shell (∼9 nm in thickness), appears in an Al–0.2Zr–0.1Sc alloy cable after thermomechanical treatment. The average diameter of the spheroidal Al3(Zr,Sc) precipitate is approximately 80 nm. The double-shelled Al3(Zr,Sc) precipitate presents three different interfaces and is semi-coherent with the Al matrix. Atom probe tomography (APT) analyses further show that the outer shell of Al3(Zr,Sc) precipitate is Sc element enrichment. The electrical conductivity of Al–0.2Zr–0.1Sc alloy cable increases by 6.5 MS/m within the aging time from 0.2 to 100 h at 350 °C, with double-shelled Al3(Zr,Sc) precipitate.

Alumina-reinforced copper matrix composites with Ag addition were fabricated by internal oxidation. The effects of slight Ag addition (0.92 at%) on electrical conductivity (EC) and oxidation resistance of internal-oxidized copper alumina composites were investigated. The annealing treatments were carried out to promote the diffusion of Ag in copper matrix. Ag was observed to segregate at Cu/Al2O3 interface after being annealed, which may lead to the lower interfacial energy between Al2O3 and copper matrix. The EC increased more than 7.8% after Ag was added. Moreover, annealing Cu Al2O3 Ag composite at 500 °C for 10 h results in the improvements of both oxidation resistance and EC. The initial oxidation temperature increased from 169 °C to 189 °C and the EC increased from 81.98 ± 0.56% International Annealed Copper Standard (IACS) to 88.19 ± 0.27%IACS. While the EC of Cu Al2O3 composites always remained ∼76%IACS which suggests that the annealing treatment has insignificant impacts on EC of Cu Al2O3 without Ag.

Four component solder alloys (Sn-3.0Ag-0.5Cu-xZr; x = 0, 0.05, 0.2, and 0.5 wt%) were obtained using vacuum induction melting. The microstructure of the solder alloys and solder joints was characterized via OM, SEM, XRD and EPMA. Tensile and shear tests were performed to evaluate the mechanical properties. The results showed that with the increase of the Zr content, the size of the primary β-Sn phases decreased gradually, and Ag3Sn decreased first and then increased. The SAC305-0.2Zr solder exhibited the finest microstructure. The size of the primary β-Sn phase decreased by 59%, and the Ag3Sn resembled a dot 1 μm in size. Tensile tests indicated that as the Zr content increased, the strength of the solder increased, and the elongation first increased and then decreased. Compared to the original joints, the joints fabricated with Zr-modified solders had thinner intermetallic compound (IMC) layers and exhibited higher shear strength. The SAC305-0.2Zr/Cu joints had a 17% reduction in the interfacial reaction layer thickness and a 20% increase in the maximum shear force. Moreover, the Zr-modified solders showed a significant decline in undercooling. The melting range and melting point was slightly reduced. In this study, 0.2 wt% was determined to be the optimum amount of Zr in the SAC305 solder.

Theoretical models for predicting the change of electrical resistivity of Al–Zr–Sc cable with Al3(Zr,Sc) core–shell dispersoids during aging were developed through integrating thin slices of core–shell cell. The theoretical electrical resistivity decreased with increasing volume fraction and size of dispersoids. As the aging time at 350 °C increased from 0.2 to 400 h, the experimental electrical resistivity of aged Al–Zr specimens decreased from 3.46 to 2.77 μW cm, and that of Al–Zr–Sc specimen decreased from 3.65 to 2.93 μΩ cm. Meanwhile, the theoretical electrical resistivity of aged Al–Zr–Sc specimen ranged from 3.6 to 2.85 μΩ cm, showing the prediction matched well the experimental results. The difference in the electrical resistivity between Al–Zr and Al–Zr–Sc specimens may be caused by the shell of the Al3(Zr,Sc) dispersoids. The possible scope of electrical resistivity difference value ranged from 0.05 to 0.20 μΩ cm.

α Macrozones are usually observed in near-α/α+β titanium alloys but have not been reported in near-β titanium alloys. This article shows that a new type of α macrozone has been observed using electron backscatter diffraction (EBSD)-orientation maps in a near-β titanium alloy Ti-5Al-5Mo-5V-1Cr-1Fe after thermo-mechanical processing. The microstructure in the macrozone was comprised of primary α plates (αp) and secondary α platelets (αs) with insignificant differences in shape. The majority of α platelets had similar orientation after aging.

The surface stability and equilibrium morphology of MoO3 were investigated by the first principles calculations. The thermodynamic energies of the stoichiometric surfaces of MoO3 are in the order (0 1 0)

Microstructure plays a crucial role on mechanical properties of materials. The as-prepared Al-Cu-Li alloy exhibits excellent thermal stability during longer aging treatment at 160 °C. Transmission electron microscopy, high angle annular dark field scanning transmission electron microscopy and first-principle energy calculations were used to evaluate the evolution of different phases in the alloy. The results show that the microstructure evolution goes as follows: SSS→δ′, θ′, T1→θ′, T1, cubic Al5Cu6Li2 phase. The cubic Al5Cu6Li2 phase was not precipitated from the matrix until 104 h aging, and the number density increased with prolonging of aging time. Its formation compensates the strength loss caused by the decreased number density and coarsening of θ′(Al2Cu) and T1(Al2CuLi) during longer aging treatment.

The precipitation behavior of a cast Al-4.5Cu-3.5Zn-0.5Mg alloy was comprehensively analyzed using differential scanning calorimetry (DSC), Vickers hardness measurement, electrical conductivity measurement, and transmission electron microscopy (TEM). The results revealed that three exothermic reactions occur during the heating process of DSC, giving rise to exothermic peaks at around 130, 250, and 280 °C due to the formation of Guinier-Preston (GP) zones and the precipitation of Ω phase and θ′ phase, respectively. TEM observations indicated that the predominant phase was the Ω phase, with only small amounts of the θ′ phase precipitating at 280 °C. STEM analysis showed that elements Zn and Mg segregate at the Ω–α interface. The precipitation of the Ω phase was remarkably promoted by the addition of Zn. The tensile strength and elongation heated up to 280 °C with the heating rate of 5 °C/min were 403 MPa and 9.2%, respectively. It was thus concluded that the precipitation sequence of the cast alloy was supersaturated solid solution (SSS)→GP zone→Ω phase→θ′ phase. The cast alloy possesses high strength and high toughness due to the predominance of the Ω phase and the lack of substantial θ′ phase.

The effect of the addition of 0.1 wt% Sc and 0.1 wt% Er on the deformation microstructure, Vickers microhardness, and electrical conductivity of Al-0.2 wt% Zr-based alloy cables annealed at 400 °C for different times was investigated. The comprehensive properties of Al-0.2Zr-0.1Sc were better than those of Al-0.2Zr-0.1Er. The optimal conditions for the Al-0.2Zr-01Sc alloy cable were a microhardness of 575 MPa, an electrical conductivity of 34.5 MS/m for an annealing time of 36 h, and those for the Al-0.2Zr-0.1Er alloy cable were a microhardness of 550 MPa, an electrical conductivity of 33.6 MS/m for an annealing time of 8 h. During the annealing process, dispersed Al3(Zr,Sc/Er) precipitates were generated, which substantially impeded recrystallization by Zener pining of grain boundaries. Based on the ratio of volume fraction (FV) to average diameter ( d ¯ ) of the precipitates, their capability to inhibit recrystallization was as follows: Al3(Zr, Sc) > Al3(Zr, Er) > Al3Zr. Moreover, the electrical conductivity of Al-0.2Zr-0.1Sc was better than that of Al-0.2Zr-0.1Er, probably because Sc could better inhibit recrystallization than Er, leading to fewer grain boundaries and hence lesser electron scattering.

In this study, the effect of Sc content on the phase transformation of the 2519 alloy during solidification is investigated through microstructure characterization and thermodynamic calculations. The results show that the grain size of the 0.3–0.4Sc alloy is reduced by 70% (approximately 28.9 μm) to achieve maximum refinement in the as-cast 2519(Sc) Al alloy. The phase diagram calculation shows that the sequence of intermetallic formation during the solidification of 2519(Sc) Al alloy is as follows: Al3Sc, W phase, θ. The primary Al3Sc particles appear at the center of the α–Al grains and evidently acted as heterogeneous nucleating agents. Transmission electron microscopy shows that the nano-sized bean-like Al3Sc phase precipitated from the saturated solid solution. Moreover, the phase transition analysis of the 0.3–0.4Sc alloy during solidification shows that the formation of the W phase underwent two different types of reactions: the peritectic-eutectic reaction (L + Al3Sc → α–Al + W) and eutectic reaction (L → α–Al + W, L → α–Al + θ + W). The W phase formation mechanism of these two reactions is revealed through experiments. Simultaneously, W phases with different morphologies are observed in the 0.3–0.4Sc alloy, i.e., the W phase of the spherical-shell structure is formed by the peritectic-eutectic reaction, and the long strip W phase (~6 μm in size) is precipitated by the eutectic reaction.

Electrical contact material's properties such as processability and switching behavior is strongly depend on the fabrication method. Here we present a study for evaluating the potential impact of fabrication technology for Ag/10SnO2 electrical contact materials. The result indicated that fabrication technology had an important influence on electrical contact physical phenomena, arc erosion morphology and arc erosion model of Ag/10SnO2 electrical contact materials. The mass change measured by volumetric method is 0.3765 mg larger than that of weighing method. In addition, the formation process and mechanism on arc erosion of Ag/10SnO2 electrical contact materials fabricated by different technology were discussed.

The influence of trace La on the oxidation of Ag-Sn alloy has been widely discussed. Here we present a detailed study for evaluating the potential impact of high content La for the oxidation of Ag-Sn alloy. We found that there are two kinds of intermetallic compounds in Ag-2Sn-4La alloy. The intermetallic compounds underwent a preferential oxidation, and the corresponded precipitation sequence of oxides was La2O3, La2Sn2O7 and SnO2. Based on the acquired insight, we suggest that high content La can accelerate the oxidation of Ag-Sn alloy oxidation but is not beneficial for the microstructure design of Ag-SnO2 electrical contact material.

The effects of Sc additions and isothermal aging on the microstructure and mechanical properties of 2055 aluminum alloy have been investigated. The isothermal aging temperatures investigated were 175 °C and 200 °C. Results show that the aging temperature does not affect the type of precipitates in both Sc-free and Sc-added 2055 Al alloys. While remarkable changes in the size and number density of T1 (Al2CuLi) precipitates have been observed. For samples aged at 175 °C for 8 h, the average length of T1 precipitates was increased from 39.9 nm to 45.6 nm, the number density decreased from 5.77 × 1022 m−3 to 3.68 × 1022 m−3 after Sc addition. On the contrary, when samples were aged at 200 °C for 8 h, the length decreased from 59.89 nm to 43.32 nm and number density increased from 2.13 × 1022 m−3 to 3.00 × 1022 m−3 by adding trace Sc. Slight deterioration of tensile strength and yield strength with higher ductility was founded at the aging temperature of 175 °C for 8 h due to the larger size and lower number density of T1 precipitates along with the formation of a W (AlCuSc) phase during the casting or homogenization processes. When aging temperature increased to 200 °C, tensile strength and yield strength were significantly improved by Sc addition without losing ductility. Highly dense fine T1 precipitates take responsible for the strength improvement, and to some extent it compensated the strength loss caused by the formation of W phase. A “vacancy-prison” mechanism was adopted to explain the effect of Sc additions on the precipitation of T1 phase as a function of aging temperature.

The morphological evolution of the stress-induced α″ martensite with increases in the stretching and rolling deformation degrees as well as the related orientation relationship were investigated in a β titanium alloy (Ti–19Nb–1.5Mo–4Zr–8Sn)·For a stretching deformation of 1%, the α″ martensite exhibited a packet morphology consisting of parallel lamellar structures. On the other hand, in the 2%-rolled sample, the α″ martensite exhibited a long lath-like distribution, which was accompanied by a few small pieces. With an increase in the deformation degree, the α″ martensite gradually exhibited a ladder-like structure consisting of long and short α″ laths or ellipsoids. The existence of these self-accommodating martensitic variants decreased the elastic energy. The parallel α″ laths present within a single packet were found to have the same orientation. The interface between the α″ and β phases was coherent, and their lattice constant relationships were identified as 2 a β ≈ b α ″ ≈ c α ″ and aβ ≈ aα″. Further, with the increase in the deformation degree, the hardness of the alloy first decreased and then increased; this was the case both the stretched as well as the rolled samples.

High-temperature compression deformation of a Zr-4 metal matrix with dispersed coated surrogate nuclear fuel particles was investigated at 750 °C–950 °C with a strain rate of 0.01–1.0 s−1 and height reduction of 20%. Scanning electron microscopy was utilized to investigate the influence of the deformation conditions on the microstructure of the composite and damage to the coated surrogate fuel particles. The results indicated that the flow stress of the composite increased with increasing strain rate and decreasing temperature. The true stress–strain curves showed obvious serrated oscillation characteristics. There were stable deformation ranges at the initial deformation stage with low true strain at strain rate 0.01 s−1 for all measured temperatures. Additionally, the coating on the surface of the surrogate nuclear fuel particles was damaged when the Zr-4 matrix was deformed at conditions of high strain rate and low temperature. The deformation stability was obtained from the processing maps and microstructural characterization. The high-temperature deformation activation energy was 354.22, 407.68, and 433.81 kJ/mol at true strains of 0.02, 0.08, and 0.15, respectively. The optimum deformation parameters for the composite were 900–950 °C and 0.01 s−1. These results are expected to provide guidance for subsequent determination of possible hot working processes for this composite. Keywords: Zr-4 metal matrix, Coated surrogate nuclear fuel particles, High-temperature deformation, Processing map, Microstructure

The effect of electrostatic potential (EP), specifically without current and Joule heating effect, on the precipitation in aluminum alloy during artificial aging (180 °C) was investigated via microhardness testing, transmission electron microscopy (TEM), positron annihilation spectroscopy (PAS), and measurements of vacancy formation enthalpy and vacancy migration enthalpy. The results elaborated that EP promoted the nucleation of solute clusters/GP zones in the early stage during aging. After extended aging, highly dense fine precipitates were retained in Al matrix leading to an improved strength. EP-assisted artificial aging provides a new pathway to tailor the precipitation behavior in Al alloys.

An intricate understanding of the fundamental β→α phase transformation upon the presence of metastable ω phase is vital for tailoring the multiphase microstructures of titanium and titanium alloys for various specific applications. To approach this, the structures and energetics of heterophase interfaces among α, β, and ω in titanium were thoroughly investigated, using the combination of high-resolution transmission electron microscopy and first-principles density functional theory calculations. The results strongly suggest that metastable ω does not necessarily act as the precursor of α but can reduce the energy barrier for α nucleation in β. The ω/β interfaces acts as favorable nucleation sites for α which, once forms, tends to grow favorably into the β matrix. These findings validate the ω-assisted α nucleation mechanism, and adequately rationalize many TEM observations on titanium alloys.

Al-Mg-Si alloys are medium-strength high-conductivity alloy cable materials that are ideal candidates for electrical engineering applications, but their related electrical conductivity, mechanical properties and textures must be studied in greater detail before such applications can be realized. Different deformation strains (0.98, 1.73 and 2.24) and annealing temperatures (200–500 °C) were applied to optimize these properties in Al-Mg-Si alloy cables. The results show that the recrystallized Al-Mg-Si alloy cables exhibit medium yield strength and higher electrical conductivity compared to the non-recrystallized Al-Mg-Si alloy cables with larger average grain sizes. After annealing, the main contributors to the overall texture were the Brass and Goss textures. According to theoretical evaluations, the significant increase in electrical conductivity and decrease in yield strength can be attributed to the decreasing dislocation density and changes to the grain boundaries.

CuSn10 matrix composites with hexagonal boron nitride (h-BN) in concentrations of 4, 7, 10, and 14 vol.% were prepared using a powder metallurgy process. The effect of modifying the h-BN with anionic polyacrylamide (APAM) by high-energy ball milling was investigated. The bonding mechanism between h-BN and APAM was characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). The microstructure, hardness, tensile strength, and bending strength of sintered composites were investigated. The composite CuSn10-4 vol%h-BN showed the lowest porosity of 20.1%. The long APAM chains could be introduced on the h-BN surface without altering its crystal structure. The surface modified h-BN exhibited less agglomeration in the matrix than pristine h-BN, due to the physical entanglement and chemical bonding between h-BN and APAM. Comparing the composites with 4 vol.% h-BN, without and with APAM modification, a reduction in the porosity from 20.1% to 5.5%, and increase in the tensile strength from 134 to 147 MPa, and a significantly increased in the bending strength from 238 to 351 MPa, respectively, were observed.

Texture and microstructure evolution of the 2524 Al-Cu-Mg cold rolled sheet in the annealing at 140–560 °C (for 1 h), was investigated carefully using X-ray diffraction, scanning electron microscopy, and electron backscatter diffraction. The characteristic texture transition rate spectral curve (CTTS), texture index, and orientation streamline approach were utilized to study the successive rules and unknown micro-mechanisms. The results demonstrated that the CTTS could precisely obtain the rule, tendency, and abnormal region of texture evolution within a large temperature range. An abnormal valley zone of texture evolution was observed at 380–440 °C, which is related to the rotation of Cube texture, and huge pinning force from the second phase. The orientation streamline approach effectively revealed the potential evolutional mechanisms of the texture, including α55° {φ1 = 55°, φ = 45°, φ2 = 0°}, Cu35° {φ1 = 35°, φ = 90°, φ2 = 45°}, and F {φ1 = 90°, φ = 55°, φ2 = 45°}. The content of ∑3 twin grain boundary and texture index FCGB weaken each other in the temperature ranges of 320–400 °C and 440–560 °C.

Undesirable damping capacity and mechanical properties resulted from coarse α-Al dendrites and network eutectoid structures of high-Zn aluminum casting alloys are the main problem restricting their practical applications. Rare-earth microalloying offers an effective means to improve the microstructure of Al alloys. Hence, in this study, the microstructure, damping capacities, and mechanical properties of newly developed Al–40Zn–xYb (x = 0, 0.1, 0.3, 0.5 wt%) cast alloys were systematically evaluated by optical microscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The experimental results indicated that Yb3Zn11 and YbZn2 intermetallic compounds were successively formed by adding Yb in Al–40Zn alloys. The α-Al grain and the α + η eutectoid structures of the Al–40Zn alloy were significantly refined with increasing Yb content. Among them, the 0.3Yb alloy exhibited the smallest grain size (approximately 157 µm) and the minimum interlamellar spacing of the α + η eutectoid structures (approximately 243 nm). Moreover, the same alloy presented partial curved α + η eutectoid structures. The 0.3Yb alloy possessed optimal damping capacity and mechanical properties; in comparison with Al–40Zn, the damping values of 0.3Yb increased by 74.7% at 300 K and by 32% at the internal friction peak P (approximately 563 K), whereas the yield strength, tensile strength, and elongation increased by 25.4%, 14.9%, and 58.6%, respectively. The remarkable improvement in damping capacity and mechanical properties was mainly attributed to the high density of grain boundaries (GBs) and fine α + η structures.

In present study, Cu-Al2O3 composites with both higher micro-hardness and electrical conductivity were fabricated by internal-oxidizing Cu-Al and Cu-Al-Ag sheets at 950 degrees C for 2 h. A small amount of Ag was doped as additives with atomic ratio of Ag/Al ranging from 0 to 0.25. Effects of Ag addition on microstructures, electrical conductivity and micro-hardness were investigated. Results show that the morphology and size distribution of Al2O3 in internal-oxidized Cu-Al alloys were highly sensitive to Ag addition. The size of Al2O3 precipitates decreased from similar to 63 nm to similar to 37 nm when increasing Ag content. Moreover, a large number of triangular Al2O3 precipitate with similar size was observed by field emission scanning electron microscope (FESEM) and high-resolution transmission electron microscopy (HRTEM) in Ag-doped Cu-Al2O3 composites. The orientation relationship between triangular Al2O3 and Cu matrix was [112](Cu)//[110](Al2O3), (11 (1) over bar)(Cu)//(002)(Al2O3) and (2 (2) over bar 0)(Cu)//(2 (2) over bar 0)(Al2O3). Increasing the amount of Ag enhances the electrical conductivity and mechanical strength simultaneously. The optimal electrical and mechanical properties which were 85.9% IACS and 162 HV respectively, were obtained when atomic ratio of Ag/Al was similar to 1: 4 in internal-oxidized Cu- Al2O3-Ag alloy.

The influence of Cr-, Nb- and W-doping on the mechanical properties of C11 b MoSi 2 has been investigated using first-principles calculations. Firstly, the formation enthalpies of both C11 b - and C40-structured MoSi 2 with various doping concentrations are calculated and compared, revealing that the C11 b structure can retain good structural stability at low doping concentrations of Cr, Nb or W up to ∼9.2 at.%. Based on the calculated elastic constants, the elastic moduli, hardness and several thermodynamic properties of doped MoSi 2 have been further predicted. Cr-doping decreases the elastic moduli drastically and W-doping decreases the Debye temperature, while doping with Nb increases the B/G ratio and Poisson ratio significantly, leading to good ductility and strong metallic bonding. As revealed in the three-dimensional contours of the elastic moduli, Cr- and W-doping does not obviously affect the anisotropy of the Young's and shear moduli, but Nb-doping shows a remarkable influence. Finally, in order to clarify the doping effects, the electronic properties of doped MoSi 2 are further discussed, based on the analysis of the charge density and density of states.

The creep behavior and microstructural evolution of 8030 alloy at 90–150 °C and 50–90 MPa of applied tensile stress were investigated by creep testing and transmission electron microscopy. The 8030 alloy possesses excellent creep resistance at low temperatures. The sizes of a small number of subgrains increase during the creep process due to subgrain merging. An Al 3 Fe phase non-uniformly pinned on the subgrain boundary made the pinned subgrains difficult to merge with the surrounding subgrains. At 90–120 °C/50–90 MPa, the stress exponent n was 5.1–5.7 and the activation energy Q c was 49.7–66.5 kJ/mol, suggesting that dislocation climb controlled by the grain boundary diffusion is the primary creep mechanism. At 150 °C, the ability of Al 3 Fe secondary phase to hinder the dislocations significantly decrease. When the tensile stress is 50–70 MPa, n = 6.8 and Q c = 49.7–66.5 kJ/mol, but n = 10.0 at a stress of 90 MPa. A creep activation energy of 123.2 kJ/mol is close to that of the lattice self-diffusion in aluminum, implying that a lattice self-diffusion mechanism is dominant at 150 °C/90 MPa.

The effect of Sc addition on creep resistance properties in the Al-0.7Fe-0.2Sc and Al-0.7Fe alloy has been studied. The microstructures before and after creep of Al-0.7Fe and Al-0.7Fe-0.2Sc alloy were investigated by optical microscopy, electron probe micro-analysis and transmission electron microscopy. In creep tests, the steady state creep rates of Al-0.7Fe-0.2Sc alloy were much lower than that of Al-0.7Fe alloy at 90–150 °C/70 MPa, it indicates that Sc addition significantly affected the creep resistance in Al-0.7Fe alloy cables. According to EPMA data and the known formation enthalpies of Al 3 Fe and Al 3 Sc phases, both of them are thermally stable. Additionally, TEM imaging showed that Al 3 Fe phases non-uniformly pinned on the subgrain boundary, and the average size of Al 3 Fe phase is approximately 0.4 µm. The nanosized Al 3 Sc precipitates (25–40 nm) both pinned on subgrain boundary and dislocation, making the pinned dislocations and subgrain boundary difficult to shift. The Orowan stress increment of ∆ σ Or in crept Al-0.7Fe-0.2Sc alloy is 61.3 MPa, whereas the ∆ σ Or of crept Al-0.7Fe alloy is 30.1 MPa, indicating that Al-0.7Fe-0.2Sc alloy cables possess higher creep resistance than Al-0.7Fe alloy cables.

The present study investigates the influence of Ce addition on the thermal behavior, microstructure, and mechanical properties of Sn-3.0Ag-0.5Cu (SAC305) solder alloy. The intermetallic compound (IMC) layer evolution and shear strength of SAC305-xCe solder joints were also studied under different aging processes. Four different alloys with Ce concentrations ranging from 0 wt% to 0.5 wt% were prepared by vacuum induction melting, followed by pouring into a steel mold and cooling to room temperature. The microstructure was characterized using optical microscopy, scanning electron microscopy, X-ray diffraction analysis and electron probe microanalysis, tensile and shear tests were conducted to evaluate the mechanical properties of the solder alloys and solder joints. The results show that the addition of Ce can refine the microstructure and improve the tensile strength of SAC305 alloys. The joints fabricated with Ce-bearing alloys possessed thinner IMC layers and slower IMC growth rate, and exhibited higher shear strength. Moreover, the addition of Ce can facilitate the aggregation of nano-Ag3Sn particles on the surface of Cu6Sn5 particles at the interface between the solder alloy and the Cu substrate. These Ag3Sn particles can act as small connection skeletons and contribute to strengthening the solder joints. The best mechanical performance during both reflowing and isothermal aging was achieved for SAC305 joints with a Ce concentration of 0.15 wt%.

The effect of varying the Cu content of Al-Mg-Si-xCu (x = 0.5, 1.0, 2.5 and 4.5, in wt.%) alloys on precipitation and their age-hardening behavior was investigated through hardness measurements, transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM). The results indicated that aging at 165 °C, the peak aging hardness increased from 109 to 218 HV with the Cu content increasing from 0.5 to 4.5 wt%. Similarly, there was an increase in the peak aging time with Cu content. However, in over-aging stage, the hardness of 4.5Cu alloy decreased more rapidly than that of 0.5, 1.0 and 2.5Cu alloys. Furthermore, an increase in Cu content brought about an apparent change in the main precipitate of the peak-aged samples from needle-shaped β″ phase in 0.5Cu alloy to: needle-shaped β″ phase and granular Q′ phase in 1.0Cu alloy, granular Q′ phase and θ′ platelets in 2.5Cu alloy, and θ′ platelets with a small amount of Q′ phase in 4.5Cu alloy.

s The effects of secondary particle-induced local recrystallization on fatigue crack growth in electromagnetically cast AA2524/Al Cu Mg T3 alloy sheets were investigated using X-ray diffraction, scanning electron microscopy, transmission electron microscopy and fatigue tests. A neck-lace-like structural model, which was composed of coarse secondary particles and fine grains, was established to describe the observations. The results showed that the fatigue crack growth rate was significantly lowered by the pronounced secondary particle-induced local recrystallization, owing to the resulting stress concentration and the microstructural scale effect. The sheets with a more dispersed distribution of the secondary particles, which corresponded to a larger inter-particle spacing, exhibited the highest fatigue crack growth resistance in the stable stage of crack extension.

The stress corrosion cracking (SCC) behavior of Ti-6Al-4 V alloy with different lamellar α microstructures in simulated oilfield brine was investigated in this study. The SCC susceptibility of the Widmanstatten sample was 11.0%, lower than that of the bimodal and trimodal samples (19.9%, and 18.0%, respectively). In the Widmanstatten sample, the crack growth path transitioned from a zigzag to a linear path when the crack moved from one colony to another because of the sliding variations in the slip bands with different orientations. The decrease in a SCC resistance of bimodal and trimodal samples resulted from the decrease in α/β colony size. Owing to the larger thickness and different orientation of lamellar α, the trimodal sample exhibited a slightly higher SCC resistance and more circuitous crack propagation than that in the bimodal sample. The deflection angle of the crack increased with an increase in the angle between the slip system, and the favorable slip system was prismatic in three samples. It can be concluded that one of the strategies to improve the SCC and crack growth resistance of Ti-6Al-4 V alloy in oil field applications is to tailor the lamellar α microstructure with different orientations and larger α colonies.

In order to improve the impact toughness of h-BN/CuSn10 composites, and to realize their industrial application in urban rail transit, we prepared Ag/h-BN/CuSn10 composites containing 3 wt% Ag using a powder metallurgy process. The microstructure of the composite was characterized by scanning electron microscopy, electron probe microanalysis, and energy dispersive spectroscopy. The transformation of the Ag-rich phase was recorded using confocal microscopy. The experimental results show that the Ag-rich binder phase, formed during the sintering process, promoted the dissolution and rearrangement of matrix particles, simultaneously filling the matrix pores. Thus, the continuity of the matrix was effectively improved, and the porosity of the composite material was significantly reduced. Compared with the original pristine composite, the relative density of the Ag/h-BN/CuSn10 composite increased from 86 to 93%, and the impact toughness significantly increased from 2.9 to 8.4 J/cm2, a 189% improvement.

The stress relaxation (SRT) behaviour and α phase evolution of Ti-55511 alloy with bimodal and lamellar microstructures were investigated at 350, 400, 450 and 500 °C. The results indicated that, the stress decreased with SRT time and the decreasing rate increased with temperature at the initial stage for both bimodal and lamellar samples. While, the stress relaxation limit (σ∞) of lamellar sample was obviously larger than that of bimodal sample at the same temperature. Dislocation annihilation and coarsening of secondary α (αS) phase always took place during SRT especially at higher temperature, and they were less significant for lamellar sample due to the fencing effect of long lamellar α (αL) on dislocations. Besides, the fragment of globular primary α phase (αp) occurred along subgrain boundaries during SRT at 500 °C which led to obvious refinement of αp. The αL in lamellar structure fractured into many pieces along local shear bands during SRT at 350 °C, and some of them coarsened and spheroidized apparently during SRT at 500 °C.

The emergence of gradient structures has realized the possibility of improving the strength and plasticity of metals simultaneously. This study analyses the effects of introducing ultrasonic and liquid nitrogen during conventional stirring and friction treatment. The results show that the mechanical properties and damage tolerance of 5083 aluminum (Al) alloy can be substantially improved by the simultaneous application of two external fields (called UNFSP specimens). The average yield strength and tensile strength of the UNFSP specimens were 58.2% and 27.5% higher than those of the as-received 5083 Al alloy without reduction in its elongation, respectively. In addition, compared with the as-received 5083 Al alloy, the threshold of fatigue crack propagation and the fracture threshold of the UNFSP specimens also increased by 62.9% and 25.7%, respectively. The main reason for these improvements was the contribution of the gradient structure with high density of geometrically necessary dislocations, thicker fine grains layer, and seriously refined Fe/Mn-containing particles.

The weld reinforcement has a strong impact on mechanical properties of MIG welded joints. This paper investigates the effect of weld reinforcement on tensile, high cycle fatigue and fatigue crack propagation properties of 5083 MIG welded joint through experimentation and numerical simulations. The results show that the existence of reinforcement significantly increases the tensile strength of the welded joint, even exceeding that of base material. But the weld reinforcement is detrimental to fatigue properties. Another significant discovery is that the weld reinforcement alters the mechanism of fatigue crack initiation and rupture relative to the smooth specimens.

This study investigated the microstructure and mechanical properties of interrupted aged cast Al–4.5Cu–3.5Zn–0.5 Mg alloy. Small Cu-rich Guinier–Preston (GP) zones and Mg-rich clusters (GPI zones) formed during the initial aging stages. Zn addition promoted the formation of a uniformly dispersed fine plate-like Ω phases in the matrix. The microstructure of the interrupted aged alloy comprised fine highly dense Ω and θ′ phases within the matrix, compared to that of isothermal aged alloy. The enhanced mechanical properties of the cast Al–4.5Cu–3.5Zn–0.5 Mg alloy were attributed to this microstructure.

Electron backscatter diffraction (EBSD) and backscattered electron imaging (BSE) were used to study the origin of microtextured region and how thermo-mechanical processing affects the macro/microtexture in near-β titanium alloys. Multi-step heat treatments were conducted on an (α+β)-warm-compressed Ti-55511 bar. It includes two-step sub β-transus annealing (830 °C, 2 h, 750 °C, 2 h) and a sub β-transus aging (600 °C, 8 h). The results show that microtextured regions, consisted of similar-shaped αp+αs lamellae and αag platelets, formed after the final aging. By analyzing the α and β texture during each thermomechanical step, the microtextured region (macrozone) formation was related to the maintained Burgers Orientation Relationship between α/β. In addition, the variant selection mechanism also leads to microtexture development.

The limited ductility and impact toughness of titanium alloys is a critical issue that limits the use of titanium alloys in the oil and gas industry. In this study, we obtained the highest impact toughness (55.7 J/cm2) for an extruded Ti–Al–V–Mo–Zr alloy tube using a three-step heat treatment. The microstructure and corresponding mechanical properties of the Ti–Al–V–Mo–Zr alloy tube were studied. We achieved significantly improved elongation (69%) and impact toughness (51%) of the Ti–Al–V–Mo–Zr alloy, contribute to the mixing coarse equiaxed and lamellar microstructure. The special heat treatment and bending lamellar microstructures play an important role in this significant phenomenon.

Numerous reports have elucidated the importance of impact toughness measurements for investigating the damage tolerance of a material. However, the effect of heat treatment parameters on impact toughness and the crack propagation mechanism in titanium alloys has rarely been addressed. Herein, the impact toughness of extruded Ti−Al−V−Mo−Zr alloy that comprises equiaxed and lamellar α microstructures has been investigated by conducting Charpy impact tests. The resulting fracture surface and alloy microstructure were examined by scanning electron microscopy, electron backscatter diffraction, and transmission electron microscopy. The obtained results revealed that the colony size decreased after a solid solution and aging treatment, whereas subcritical annealing and slow cooling led to the globularization of lamellar α grains. After globularization, the impact toughness of the alloy increased by 69.2% and 50.0%, respectively; however, the impact toughness of the sample after the solid solution and aging treatment decreased by 61%. During impact testing, the direction of crack propagation was oriented toward the low-angle boundary region. Furthermore, a dissolved secondary phase was formed in the vicinity of the fracture surface, which increased the resistance of the alloy to crack propagation. The present study provides significant guidance for the preparation of titanium alloys with superior impact toughness properties.

External oxidation was adopted to fabricate Cu–Al2O3 composites with Ag addition. The influences of Ag on oxidation kinetics, microstructure evolution and properties of Cu–Al2O3 composites were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and optical microscopy (OM). The external oxidation was found to be the combination of surface oxidation and internal oxidation. The parabolic rate constant (PRc), which can reflect the oxidation rate during the internal oxidation process, was analyzed by experimental measurement and theoretical calculation. The measured PRc results during external oxidation have increased by 81% to 2.14 × 10 − 8 cm2/s at 1073 K and 71% to 2.63 × 10 − 7 cm2/s at 1223 K after Ag was added. It indicates that the Ag can remarkably accelerate the internal oxidation process in external oxidation. Moreover, compared with traditional internal oxidation method, the external oxidation was found to be a more efficient way to prepare Cu–Al2O3. The PRc in traditional internal oxidation are 3.58 × 10 − 9 cm2/s at 1073 K and 6.72 × 10 − 8 cm2/s at 1223 K, while the PRc in external oxidation are much higher which are 1.18 × 10 − 8 cm2/s at 1073 K and 1.54 × 10 − 7 at 1223 K. SEM results show that the oxide bands composed of coarsening Al2O3, have disappeared, and the size of Al2O3 precipitates dropped from ∼65.78 nm to ∼45.42 nm after Ag was added. Due to the more homogeneous microstructure caused by Ag, the electrical conductivity had a 9.48% increment to ∼85.27% International Annealed Copper Standard (IACS), and the microhardness climbed from ∼131.8 HV to ∼152.76 HV.