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We modified the morphology and distribution of copper-bearing precipitates in an Al-Mg-Si-Cu alloy and obtained ultra-high comprehensive properties through a modified thermo-mechanical treatment composed of aging and cold deformation. The precipitate evolution and atomic structure was observed by employing atomic resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). Our results proved the existence of β′′/Q′ composite precipitates in rod-like morphology after aging treatment due to the inhibition of β′′ phase formation by copper atoms. We also revealed that the peak-aged phases transformed into in-situ reverse-transformed Guinier Preston zones (GP zones) during the deformation process. By the means of modifying the precipitates, we finally simultaneously obtained ultra-high strength (424.40 MPa) as well as favorable conductive properties (52.78%IACS), both of which surpassed three mainstream standards for high strength aluminum conductor.

The effect of Sc-microalloying and Y2O3 nano-particles on the microstructure and mechanical properties of as-cast Al-5.5Si alloy is studied by means of optical microscopy, transmission electron microscopy, hardness test and tensile test. The influence of annealing treatment on the microstructure and properties of the Al-Si alloys is also investigated as well. The results show that the addition of Sc and Y2O3 nano-particles could significantly improve the mechanical property of the Al-Si alloy. The ultimate tensile strength and yield strength of Al-Si-Sc/Y2O3 alloy are improved by around 45 and 71%, respectively, when compared to that of the Al-Si alloy. The effect of the nanosized particles (precipitated and added) on strengthening and deformation of Al-Si alloy is analyzed and discussed in detail. The results of annealing treatment indicate that the change in mechanical property of the Al-Si-Sc alloy during annealing treatment is mainly associated with the precipitation of the secondary Si phase.

In the present work, the influence of stress concentration and deformation temperature on the mechanical behavior of boron carbide particles reinforced aluminum matrix (B4Cp/Al) composites fabricated by powder metallurgy was investigated via the tensile test and finite element simulation based on the real microstructure. The results demonstrate that a uniform particle distribution and a good interface bonding between the particles and matrix are found in the 5 wt% B4Cp/6061Al composite. When the deformation temperature decreases from 298 to 77 K, the tensile property and notch sensitivity ratio of the notched composite increases. Combined with the microstructure observation and stress/strain evolution, the fracture mechanism of the notched composite at 77 K was revealed. Specifically, there is a difference in stress and strain distributions induced by deformation temperature in the initial stage of deformation of the notched composite. The matrix damage tends to occur from the notch and propagate to the high strain regions near the particles. Furthermore, there is a high possibility of particle fracture or interface debonding in the notched composite due to the high matrix stress at 77 K. This work provides the experimental and theoretical basis for the application of particle-reinforced aluminum matrix composites with stress concentration under cryogenic environments.

In this paper, high-strength steel is prepared by different heat-treatment processes. Through split Hopkinson pressure bar experiment, optical microscope, scanning electron microscope and X-ray dif...

The microstructure and tensile property of the hypoeutectic Al-Si alloy with and without microalloying of Sc and Zr were studied by means of the optical microscope (OM), Transmission electron microscopy (TEM) and the tensile test. The focus of this work is the effect of microalloying and tensile deformation on the internal structure (i.e. nanoscale precipitates and the stacking faults) in eutectic Si phase. The results show that the nanoscale precipitates are evident in eutectic Si phase in Al-Si alloy without any special heat treatment or modification. The additions of Sc and Zr into the Al-Si alloy increased the size of the nano precipitates, and significantly promoted the formation of the stacking faults inside the eutectic Si phase. Moreover, the eutectic Si phase experienced twinning deformation during the tensile deformation of the Al-Si based alloy, and this twinning deformation was more pronounced with increasing the tensile strength of the Al-Si based alloy. It is proposed that the deformation of the eutectic Si phase also contributed to the property and the ductility of the Al-Si based alloy.

Al-3Fe alloy was prepared by the method of continuous rheo-extrusion, and the effect of rolling deformation on the microstructure and the property of the rheo-extruded Al-3Fe alloy was studied by means of scanning electron microscope (SEM), transmission electron microscopy (TEM) and tensile test. The rheo-extruded pure Al was also prepared for comparison. The results showed that the rolling deformation could further refine the grain size of the rheo-extruded Al-Fe alloy, and reduce the size of the Al-Fe phase. Due to the present of nanosized and sub-micron sized Al3Fe phase, the strength of rheo-extruded Al-Fe alloy is significantly higher than that of rheo-extruded pure Al, and this advantage has been maintained during subsequently rolling deformation. Moreover, the strength and the elongation are simultaneously increased when the rolling reduction exceeds 60% for Al-Fe alloy and pure Al. Both of Al-Fe alloy and pure Al have the best comprehensive mechanical property when the rolling reduction reaches 90%. The main contribution is attributed to the grain refinement and the formation of high fraction substructure. Keywords: Al alloy, Rheo-extrusion, Deformation, Microstructure, Property

The melt temperature of aluminum alloys plays a significant role in determining the microstructure characteristic during continuous rheo-extrusion. However, it is difficult to measure the actual melt temperature in the roll-shoe gap. In this work, based on the basic theory of heat transfer, a calculation model for heat transfer coefficient of cooling water/roll interface and melt/roll interface is established. In addition, the relationship between the temperature at the melt/roll interface and the velocity of cooling water is investigated. Combined with the CALPHAD calculation, the melt temperature during solidification in the continuous rheo-extrusion process is calculated. Using this model, the cooling rate of an Al–6Mg (wt.%) alloy melt prepared by continuous rheo-extrusion is estimated to be 10.3 K/s. This model used to determine the melt parameters during solidification provides a reference for optimizing the production process of continuous rheo-extrusion technology.

Graphene has been successfully coated with a nano-Al layer through a novel activating treatment (i.e., organic aluminum reduction method). The nano-Al coated graphene was further processed into AlSi10Mg alloy based composites through a selective laser melting (SLM) process. During the nanocoating of Al on graphene, Al atoms deposited on the graphene through organic aluminum reduction gradually, via nucleation and growth process. There were two primary grain growth patterns: two dimensional (2D) layered growth and three dimensional (3D) island growth, until graphene was coated with Al. The Al-coated graphene was added to the AlSi10Mg alloy, refining the cell, increased the tensile strength, hardness and wear resistance of the alloy. Coating Al on the graphene improved the wetting between graphene and Al, and the addition of Al-coated graphene led to a high nucleation rate, which was responsible for refining the cell. This approach facilitated graphene homogeneous distribution in the Al alloy, the interface between graphene and Al was relatively stable, and the grapheme could pin the dislocation and grain boundary. All these attributes enabled superior mechanical properties to be obtained in the final alloy based nanocomposites.

In order to investigate the effects of solid solution atoms, precipitated particles and cold deformation on the microstructures and properties of Al–Sc–Zr alloys, the Al–Sc–Zr alloys prepared by continuous rheo-extrusion were treated by thermomechanical treatment, analyzed for conductivity and mechanical properties by tensile and microhardness testing, and characterized using optical microscope, TEM and STEM. A mathematical model was established to quantitatively characterize the contribution of solid solution atoms, precipitates and cold deformation to the conductivity of the alloy. The results show that the strength of Al alloy can be significantly improved by solid solution, aging and cold deformation, and the quantitative impacts of solution atoms, precipitates and cold deformation on the conductivity of Al alloy are 10.5% (IACS), 2.3% (IACS) and 0.5% (IACS), respectively. Aging and cold deformation treatments are the keys to obtain high-strength and high-conductivity aluminum alloy wires.

Homogeneous graphene dispersion and suitable interface bonding are two key challenges to realize the high strengthening potential of graphene in metal matrix composites (MMCs). In this study, graphene nanosheets (GNSs) with deposited nickel (Ni) nanoparticles were synthesized to simultaneously overcome the two challenges. Ni-coated-GNS-reinforced aluminum (Al) MMCs were fabricated by graphene synthesis, Ni decoration and subsequent powder metallurgy. It was revealed that Ni-coated GNSs exhibited noticeably enhanced strengthening effect compared with graphene reinforcements in most previous studies. With the addition of 1.5 wt% Ni-coated GNSs, the composites exhibited 132% higher strength than that of unreinforced aluminum. The enhancement in Vickers hardness and Young's modulus further confirmed the remarkable strengthening effect. The high strength and high Young's modulus were examined by strengthening models, and a comparison between experimental and theoretical values was reached. The main strengthening mechanisms in the Ni-coated GNSs/Al composites were clarified as dislocation-related ones.

Al–1Fe (wt%) alloy containing nanosized Al3Fe phase was processed by continuous rheo-extrusion, and subjected to heat treatment at different temperatures. During heat treatment, due to the diffusion of Fe atoms, the nanosized Al3Fe phase was blunted and fragmented along the width direction, and the bluntness and fragmentation resulted in the spheroidization of Al3Fe phase. However, with the extension of heat treatment time, the spheroidized Al3Fe phase became coarse and grew along a particular plane. Then, the morphology of Al3Fe phase transformed into small plate-like. While, the plate-like Al3Fe phase with an average length of 30 µm in the as-cast Al–1Fe (wt%) alloy indicated good thermal stability during heat treatment. The different thermal stability of Al3Fe phases was attributed to their size. The large surface curvature of nanosized Al3Fe phase significantly accelerated the diffusion of Fe atoms. When the heat treatment temperature was 200 ℃ and 300 ℃, the tensile strength and elongation of the rheo-extruded Al–Fe alloy marginally decreased. The decrease of tensile strength and the decrease of elongation increased when the heat treatment temperature was greater than 400 ℃. The tensile strength and elongation of as-cast Al–1Fe (wt%) alloy were insignificantly altered. Though the loss of tensile strength of Al–Fe alloy containing nanosized Al3Fe phase was much greater, its tensile strength was always higher than the tensile strength of the as-cast Al–Fe alloy in the entire heat treatment.

Inconel 718 (IN718) superalloy has been fabricated by selective laser melting (SLM) technology, and the effects of the solution and double aging treatment on the microstructures and mechanical properties of the alloy have been studied. Under the same aging condition, the hardness of the IN718 superalloy first increased and then decreased with the increasing of the solution temperature. When the solution temperature was 980 °C, the average microhardness of the alloy was increased to 502 HV0.2, with 17.56% increase. With the solution temperature increasing, more short-rod δ phase (Ni3Nb) was precipitated at the grain boundaries and distributed homogeneously, and the γ′′ phase (Ni3Nb) and the γ′ phase (Ni3(Al, Ti)) were formed. The δ phase (Ni3Nb) can pin grain boundary, inhibit the grain growth and improve the mechanical properties. In addition, the corrosion resistance of the alloy decreased after heat treatment. After heat treatments, the formation of the second phase subsequently increased the number of corrosion microbatteries and reduced the anticorrosive ability of the alloy.

Influence of a static 1 T magnetic field on the phase formation and solidified microstructure of Mg-24 wt%Nd alloy at the cooling rates of 6 °C/min and 14 °C/min is studied. Metastable Mg12Nd appears at 14 °C/min and 0 T, while the equilibrium phase Mg41Nd5 is obtained at the same cooling rate and 1 T. The magnetic field induces the orientation of α-Mg dendrites and leads to the increase of compression strength of alloy (from 153 ± 3.6 to 167 ± 4.4 MPa). The contribution of magnetic field on Gibbs free energy is evaluated for the two phases. Combining with the CALPHAD method, transient nucleation theory and differential scanning calorimetry, the critical undercooling Δ T c for Mg12Nd and Mg41Nd5 is analyzed to understand the promotion effect of magnetic field on equilibrium Mg41Nd5. The Δ T c of Mg12Nd phase increases under 1 T magnetic field which is greater than that of Mg41Nd5 (11 °C) at the cooling rate of 14 °C/min.

Multilayer reduced graphene oxide (mrGO) was chemically modified by electroless plating of copper on surface to form mrGO-Cu. The scanning electron microscope (SEM) and transmission electron microscope (TEM) analysis revealed that nano-Cu particles were uniformly dispersed on the surface of mrGO. The mrGO-Cu powders were further utilized as reinforcements for aluminum (Al) matrix and the mrGO-Cu/Al composite was successfully fabricated through clad rolling of milled powder. The tribological properties of the mrGO-Cu/Al composites were explored. The tribological results show that the mrGO-Cu could reduce the friction coefficient and wear loss of mrGO-Cu/Al composites, since the mrGO-Cu participated in lubricating processes due to the formation of a transfer layer on the contact surface. Furthermore, it is found that the composition of mrGO-Cu could significantly influence the tribological properties of the mrGO-Cu/Al composites. The composites with 4% of mrGO-Cu for composites exhibited the best tribological behavior, which transformed from adhesive wear to abrasive wear, due to the formation of a graphite lubricating film.

The microstructure and mechanical properties of Al-0.35Fe alloys with a series of different zirconium (Zr) additions from 0.1 to 0.4% are investigated by optical microscopy, scanning electron microscopy, transmission electron microscopy and tensile testing. The as-cast structure of the alloys varies with the Zr content. When the content of Zr is 0.1%, Zr dissolves into the aluminum (Al) matrix completely and iron (Fe) concentrates along the boundary in a network of eutectic Al3Fe. With the increase in Zr content to 0.2% and above, nanoscale Al3Zr particles appear in the alloy. With the Zr content increasing from 0.1 to 0.4%, the grain size of the Al matrix decreases from 73 to 23 μm. The morphology of the eutectic Al3Fe phase changes from short rod-like to an agglomerated structure consisting of finer and shorter rod-like shapes. The tensile and yield strengths increase while the total elongation decreases with increasing Zr content. The strengthening mechanism of the alloy can be attributed to the combination of fine-grain, solution and second-phase strengthening.

Laser welding is widely used for the joining of aluminum alloy in the automotive industry, and the vehicles produced are inevitably subjected to high strain rate loading during their service. Therefore, this paper studied the mechanical properties of 6061-T6 aluminum alloy and its laser welded joint at strain rates between 0.0003 and 1000 s&minus, 1. Results showed that the microstructure of welded material (WM) was much finer than base material (BM), typical columnar crystals grew perpendicularly to the fusion line, and the minimum hardness value (~56 HV) was obtained inside WM. The strength and dynamic factors of BM and WM increased with increasing strain rate, and the strength of WM was less sensitive to strain rate compared with BM. The strain rate effect was not homogenous in the plastic deformation region. The modified Johnson&ndash, Cook (J&ndash, C) model which introduced the term C = C1 + C2&middot, &epsilon, could well describe the dynamic plastic deformation of BM. However, the fitted results of the simplified J&ndash, C model were overall better than the modified J&ndash, C model for WM, especially for high strain rate (1000 s&minus, 1). These findings will benefit the determination of the dynamic deformation behavior of laser welded aluminum alloy under high strain rates, and could provide a better understanding of lightweight and the safety of vehicles.

Low-cost heat-resistant Al-Sc-Zr-Fe conductor wires were successfully manufactured by continuous rheo-extrusion process, and the mechanical and conductive properties of the materials were analyzed and compared after three different thermo-mechanical treatment methods. The coarse plate-shape Al3Fe phase transformed to small sized rod-like phase after solid solution treatment at 630 &deg, C for 21 h. Direct aging treatment at 300 &deg, C for 24 h led to the refinement and spheroidization of Al3Fe phase with a diameter of 200 nm. After the subsequent aging treatment at 300 &deg, C for 24 h, the tensile strength and conductivity of the alloy wire significantly increased due to the homogeneous precipitation of the coherent spherical Al3(Sc, Zr) phase with an average size of 15 nm. The tensile strength, elongation, and conductivity of the alloy conductor wire after optimized thermo-mechanical treatment reached 165.7 MPa, 7.3%, and 60.26% International Annealed Copper Standard (IACS), respectively. The thermal resistance of the present alloy wire was superior to that of standard AT1 type alloy conductor according to IEC international standard.

Al-Cu single crystals with different typical orientations (i.e., (001), (101), and (111)) were prepared to investigate the corrosion behavior of the Al-Cu alloy with and without precipitates by scanning electron microscopy (SEM), transmission electron microscopy (TEM), immersion testing in EXCO solution, and electrochemical impedance spectroscopy (EIS). The results showed that the corrosion rates of the alloy with different orientations increased in the order of (111)

Addition of Al-5Ti-1B alloy to molten aluminum alloys can refine α-Al grains effectively and thereby improve their strength and toughness. TiAl3 and TiB2 in Al-5Ti-1B alloy are the main secondary-phase particles for refinement, while the understanding on the effect of their sizes on α-Al grain refinement continues to be fragmented. Therefore, Al-5Ti-1B alloys with various sizes and morphologies of the secondary-phase particles were prepared by equal channel angular pressing (ECAP). Evolution of the secondary-phase particles during ECAP process and their impact on α-Al grain refinement were studied by X-ray diffraction and scanning electron microscope (SEM). Results show that during the ECAP process, micro-cracks firstly appeared inside TiAl3 particles and then gradually expanded, which resulted in continuous refinement of TiAl3 particles. In addition, micro-distribution uniformity of TiB2 particles was improved due to the impingement of TiAl3 particles to TiB2 clusters during deformation. Excessively large sizes of TiAl3 particles would reduce the number of effective heterogeneous nucleus and thus resulted in poor grain refinement effectiveness. Moreover, excessively small TiAl3 particles would reduce inhibitory factors for grain growth Q and weaken grain refinement effectiveness. Therefore, an optimal size range of 18–22 μm for TiAl3 particles was suggested.

Due to superior mechanical properties and corrosion resistance, aluminum alloys with high magnesium content varying from 3 to 10 wt% have been widely used as aircraft welding wire and automotive materials. However, it remains challenging to produce high magnesium containing aluminum alloys in wire form through conventional casting, extrusion and rolling. Therefore, the present work employs continuous rheo-extrusion to manufacture Al alloy wires with high magnesium contents, which can eliminate the formation of coarse dendrites and thus improve mechanical properties. Microstructures and properties of the alloy wires were investigated by metallurgical microscopy, X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Results show that coarse dendrites were completely converted into equiaxed grains. A solid solution with high solubility of Mg and nanosized Al3Mg2 phases were formed in the alloy due to the high cooling rate in continuous rheo-extrusion. Such microstructural features incurred serrated plastic deformation in tensile tests due to the interactions between the solid solution atoms and dislocations. With increasing magnesium content, ultimate tensile strength increased while the elongation decreased gradually. Ultimate tensile strength and elongation of Al-5Mg (wt%) alloy wires were improved by 73% and 8% than that of conventional casting respectively.

The Mg-3Sn-1Mn-1La alloy sheets were prepared by a continuous rheo-rolling process, and the effects of the solution and aging treatment on the microstructures and mechanical properties of the alloy were studied. The tensile strength and elongation at room temperature and 150 °C of the Mg-3Sn-1Mn-1La alloy sheets were decreased with increasing the solution time. The grain size was increased gradually. The plate-shaped MgSnLa compounds composed of La5Sn3, Mg2Sn and Mg17La2 phases and Mg2Sn phase gradually disappeared. At the same time, new irregular MgSnLa compounds were formed in grains. Aging treatment of the alloy was performed after solution treatment. The new spherical MgSnLa compounds composed of La5Sn3, Mg2Sn and Mg17La2 phase were formed, increased and distributed gradually homogeneously in the matrix with increasing the aging treatment time. Meanwhile, the Mg2Sn phases with spherical, short-rod and lath-shaped were formed in the matrix. After solution treatment at 550 °C for 24 h, aging at 250 °C for 48 h, the tensile strength at room temperature and at 150 °C of the Mg-3Sn-1Mn-1La alloy sheet was increased to 270 MPa and 233 MPa, with 19% and 20% increase, respectively. The elongation at room temperature and 150 °C was increased to 7.9% and 67.5%, with 6% and 4% increase, respectively. The formed spherical MgSnLa compounds and Mg2Sn phases which were coherent with the matrix and effectively pinned the dislocations and grain boundaries were responsible for the enhanced mechanical properties of the alloys.

In this paper, an innovative semisolid rheo-rolling process of Mg–3Sn–1Mn alloy was proposed; the temperature distribution and its influence on microstructure of Mg–3Sn–1Mn alloy during the semisol...

Al-1Fe (wt%) alloys containing nanosized Al3Fe phase and micrometer-sized Al3Fe phase were prepared by continuous rheo-extrusion and casting, respectively. The yield strength, tensile strength and elongation of Al-1Fe (wt%) alloy containing nanosized Al3Fe phase were 128.2 MPa, 135 MPa and 30%, respectively, while that of Al-1Fe (wt%) alloy containing micrometer-sized Al3Fe phase were 81.6 MPa, 87.1 MPa and 26.8%, respectively. The influence of nanosized Al3Fe phase on the mechanical properties of Al-Fe alloy was investigated by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM), and compared with pure Al. The results suggested that the improvement of yield strength was 80.6 MPa and the reduction of elongation was 4.2% induced by nanosized Al3Fe phase. However, for the micrometer-sized Al3Fe phase, the increment of yield strength was only 32.8 MPa and the loss of elongation was 6.5%. When Al3Fe phase was refined to nanosize, its number density was increased, and the Orowan strengthening effect was significantly better. Micro-cracks around Al3Fe phase gradually grow and connect to one another with the accumulation of stress concentration and incompatible deformation. The rapid propagation of crack led to failure of the alloy. The crack around the hard Al3Fe phase became smaller once Al3Fe phase was refined, and it took a longer time for crack growth to occur. Thus, alloys containing nanosized Al3Fe phase shown superior plasticity. However, the deformation incompatibility between the matrix and the hard Al3Fe phase could not be completely eliminated even when the Al3Fe phase was refined to nanosize.

To understand the synergistic effect of TiAl3 and TiB2 particles on grain refinement of α-Al, equal-channel angular pressing (ECAP) of Al-5Ti-1B (wt%) alloy was carried out. The ECAPed Al-5Ti-1B (wt%) alloy was characterized by X-ray Diffraction (XRD), electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM). The results reveal that α-Al grains and TiAl3 phase of ECAPed Al-5Ti-1B (wt%) alloy were refined, while the average size of TiB2was marginally decreased. The tensile strength was increased from 128 MPa to 218 MPa, and the elongation was reduced from 26% to 20.6%. The transformation from dislocations to low-angle grain boundaries (LAGBs) and high-angle grain boundaries (HAGBs) resulted in continuous dynamic recrystallization (CDRX), which induced grain refinement during ECAP. From 3 to 6 passes of ECAP, CDRX occurred in the alloy, and as ECAP passes increased to 9, the rate of formation of LAGBs and the transformation rate from LAGBs to HAGBs reached a dynamic balance. The present study indicates that the second phase particles promote the formation of LAGBs but prolong complete-recrystallization time, such that complete-recrystallization leads to grain refinement. TiB2 particles are smaller than TiAl3 particles and this is caused by the composition of the alloy and its synthesis method, and compared with TiAl3, TiB2 with a smaller size had a more obvious influence on the formation of LAGBs and grain refinement.

Common strengthening strategies for casting aluminum alloys sacrifice ductility. Herein, the strength-ductility synergy of a rheo-diecasting semi-solid Al–Si–Mg–Cu–Fe–Sr alloy was tailored by optimizing the pouring temperature and subsequent heat treatment. The results demonstrated that with decreasing pouring temperature from 700 °C to 670 °C, the average grain diameter of primary α-Al grains and porosity decreased, while the average shape factor and solid phase fraction increased, resulting in improved mechanical properties of the alloy. After T6 heat treatment, changes in the morphologies of eutectic Si phases and Al3Fe phases were observed, and Mg2Si precipitates were formed, which further enhanced the mechanical properties of the alloy.

In this work, based on the A356 alloy, a novel Al–Si–Mg–Cu–Fe–Sr alloy with good mechanical property and high thermal conductivity was developed. The semi-solid slurry of the alloy was prepared via the vibrating contraction inclined plate. The microstructure evolution and solidification behavior of the alloy were investigated. The results demonstrated that, compared with the A356 alloy, the enhanced property of the Al–Si–Mg–Cu–Fe–Sr alloy was associated with the size of primary α-Al grains and morphology of eutectic Si phases. In addition, the preparation process parameters of semi-solid slurries, including the pouring temperature, inclination angle, and vibration frequency, had a crucial effect on the size and morphology of primary α-Al grains. The optimized pouring temperature, inclination angle, and vibration frequency were 670 °C, 45°, and 60 Hz, respectively. In this condition, for the primary α-Al grains, a minimum grain diameter of 64.31 µm and a maximum shape factor of 0.80 were obtained. This work provides a reference for the application of the alloy with high performance in the field of automobile and communication.

Cu‒Cr alloy is a kind of functional and structural integrated material with excellent comprehensive mechanical and electrical properties. However, due to the low solubility of Cr in Cu and the huge difference in melting point, the existing methods to manufacture well-structured Cu‒Cr alloys are facing many challenges. In this paper, laser additive manufacturing (LAM) is applied to manufacture CuCr30 with ideal structure, taking advantage of its characteristics such as the small molten pool and fast crystallization. A small amount of microporosity defects formed during the LAM process were then reduced by severe shear deformation in the subsequent continuous extrusion process. As a result, the strength of the CuCr30 was increased by 55.3% and the room temperature conductivity was increased by 6.6%. Although the Cu grain refinement leads to fine grain strengthening and the homogenization of Cr distribution leads to enhancement of second phase strengthening during continuous extrusion, both have a negative effect on conductivity, the room temperature conductivity of CuCr30 did not decrease, because of the reduction of pore defects and the formation of nano-twinned structure with thickness of 10–30 nm, which improves the strength without affecting the conductivity.

In this work, the shear model of metal melt flowing on vibration surface is established, and coupling effects of vibration and shear on the distribution of shear stress in melt and melt solidification microstructure are analyzed. Calculation results show that the transition of melt from laminar flow to turbulent flow occurs earlier with increasing vibration frequency and vibration amplitude. In the laminar flow melt, shear stress in melt decreases with increasing vertical length, but it decreases firstly and then stabilizes with increasing flow length. In the turbulent flow melt, shear stress decreases firstly and then stabilizes with increasing vertical length, but it increases with increasing flow length. With the increase in vibration frequency and amplitude, shear stress along flow direction in laminar flow melt increases, while shear stresses along both flow direction and vertical direction in turbulent flow melt increase. Shear stress in melt decreases with increasing length along vertical direction. With the increase in flow length, shear stress decreases firstly and then stabilizes in laminar flow melt, while it increases in turbulent flow melt. With the increase in vibration frequency and amplitude, shear stress increases in laminar flow melt, while it stabilizes in turbulent flow melt. Based on theoretical calculation, the maximum shear stress in melt during vibration shear flow is always much lower than the yield strength of α-Al grain, so the shear stress induced by vibration shear flow cannot break columnar crystal, which agrees with the experiment result. So, the model can explain the shear constitutive relation of melt flow on vibration surface relatively well.

Ductility and electrical conductivity of metallic materials are inversely correlated with their strength, resulting in a difficulty of optimizing all three simultaneously. We design an Al-Sc-Zr-based alloy using semisolid extrusion to yield a good trade-off between strength and ductility along with excellent electrical conductivity. The Al-0.35Sc-0.2Zr wire with a diameter of 3 mm exhibited the best combined properties: a tensile strength of 210 ± 2 MPa, elongation of 7.6% ± 0.5%, and an electrical conductivity of 34.9 ± 0.05 MS/m. The average particle size of nanosized Al3(Sc, Zr) precipitates increased from 6.5 ± 0.5 nm to 25.0 ± 0.5 nm as the aging time increased from 1 h to 96 h at 380 °C, accompanied by the corresponding volume fraction variation from (6.2 ± 0.1) × 10−4 to (3.7 ± 0.1) × 10−3. As proved by transmission electron microscopy observation, the high strength originates from the effective blockage of dislocation motion by numerous nanosized Al3(Sc, Zr) precipitates whilst both electrical conductivity and ductility remain at a high level due to the coherent precipitates possessing an extremely low electrical resistivity.

The addition of trace La significantly affected the properties of the Al–Zn–Si coating. Adding La improved the corrosion resistance of the coating. More importantly, it restrained the nucleation of α-Al dendrites consequently leading to coarser grains. Based on the density functional theory calculations, we found that the doping concentration was important to the spontaneous nucleation of the heterogeneous nucleus in liquid metal, and there should be a transition between homogeneous nucleation and heterogeneous nucleation.

Continuous preparation of high-conductivity and high-strength aluminium alloy cable remains a challenge. Here we reveal the scientific significance of high electrical conductivity Al-Ag-Sc-Zr alloy with ultrafine grains prepared by novel processing technologies, the combination of rheo-extrusion and accumulative continuous extrusion forming. Attributed to the continuous dynamic recrystallization during rheo-extrusion, equiaxial microstructure and significantly refined grains (2.8 ± 0.2 μm) were achieved. By means of partially replacing low conductive scandium and zirconium solute atoms with high conductive silver solute atoms, the processed alloy wires exhibit significant higher electrical conductivity (53.5 ± 0.4 %IACS) than the Al-Sc-Zr alloy with similar atomic concentration of alloying elements. Appropriate mechanical properties were also obtained due to the similar solution strengthening effects of silver atoms to scandium and zirconium atoms. These results highlight the potential of this high electrical conductivity Al-Ag-Sc-Zr alloy and its novel processing route.

In this study, the micro-alloying of rare-earth yttrium (Y) was employed to improve the fracture behavior and work-hardening ability of H13 die steel. The improved work-hardening ability was attributed to modification of Cr23C6 and VC carbides by the addition of Y. The strip-typed Cr23C6 carbides originally distributed along the grain boundary were interrupted and tended to spheroidize with increasing Y content. Compared with 0Y–H13 steel, the quantity of spherical VC carbides significantly increased in 0.013Y–H13 steel. A higher-density dislocations and intensive interaction between precipitates and dislocation led to a higher work-hardening exponent. Additionally, fractographic studies revealed that the fracture mode transition from cleavage failure to ductile rupture with increasing Y content. Moreover, excess Y content (0.044%) resulted in the appearance of inclusion clusters in dimples, which were detrimental to fracture and work-hardening behavior.

Grains of Al–1Si(wt%) alloy were refined by accumulative continuous extrusion forming (ACEF). Electron backscatter diffraction and transmission electron microscopy were used to analyze the microstructure evolution of the Al–1Si(wt%) alloy. The grain size of the alloy decreased from 54.36 to 2.59 μm after four passes of ACEF. The grain refinement was attributed to continuous dynamic recrystallization (CDRX). The enhanced effect of nanosized precipitates on CDRX was pronounced. Nanosized eutectic Si precipitates retained a high density of dislocations in the alloy by promoting their generation and pile-up, resulting in an increase in the driving force for CDRX and a consequent promotion of grain refinement. After 4 ACEF passes, the tensile yield strength of the alloy at room temperature increased from 102 MPa to 117 MPa. Further, the elongation of the alloy at room temperature decreased from 38 to 17 % after 3 ACEF passes and subsequently increased to 23 % after 4 ACEF passes.

The grain of an Al 0.2Er alloy (wt%) was refined by accumulative continuous extrusion forming (ACEF). Microstructure of the Al Er alloy subjected to ACEF was investigated through electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The results revealed that the formation of ultra-fine grains results from a type of continuous dynamic recrystallization (CDRX) that is induced by large strains. With the accumulation of strain, LAGBs gradually introduced and transformed into HAGBs, which leads to an increase in the average orientation angle. The micro-grain alloy is refined through repeated passes of the continuous extrusion forming process and the average grain size of the Al 0.2Er (wt%) alloy decreased from 26.01 μm to 1.3 μm in four passes. The Al 0.2Er (wt%) alloy had a smaller average grain size than that of pure aluminum. The formation of precipitates in Al Er alloy can stimulate the nucleation of CDRX by increasing the local strain energy and slow the growth of recrystallization grains by limiting grain boundary migration that causing grain refinement.

The crystal structure together with the magnetic and magnetocaloric properties in RE2Ni1.5Ga2.5 (RE = Dy, Ho, Er and Tm) have been investigated systematically. All the RE2Ni1.5Ga2.5 compounds crystallize in a CaIn2-type structure of (P63/mmc space group). A second-ordered magnetic phase transition (SOPT) from ferromagnetic to paramagnetic (FM to PM) is occurred in RE2Ni1.5Ga2.5 compounds with the Curie temperatures (TC) of approximately 16.1, 10.6, 4.1 and below 2 K for RE of Dy, Ho, Er and Tm, respectively. The magnetocaloric parameters including magnetic isothermal entropy change/temperature-averaged magnetic entropy change -ΔSMmax/TEC (5) and relative cooling power RCP are calculated with the values of 10.01/9.92 J/kg K and 418.6 J/kg for Dy2Ni1.5Ga2.5, 20.12/19.65 J/kg K and 644.1 J/kg for Ho2Ni1.5Ga2.5, 18.07/17.69 J/kg K and 447.1 J/kg for Er2Ni1.5Ga2.5, as well as 18.22/16.75 J/kg K and 330.7 J/kg for Tm2Ni1.5Ga2.5 with magnetic field change (ΔH) of 0–7 T, respectively. Notably, Ho2Ni1.5Ga2.5 exhibits ralatively high magnetocaloric parameters, which suggests that Ho2Ni1.5Ga2.5 is a competitive candidate among the MCE materials in the field of cryogenic magnetic refrigeration (MR).

To reveal the formation and wear mechanisms of rheo-formed aluminum alloy - B4C composites, A356 alloy − 10 mass% B4C composite material was fabricated by semi-solid stirring rheo-casting and rolling process. The presence of Al3BC was confirmed by XRD analysis and hinted that chemical bonding formed at interfaces between aluminum matrix and B4C particles. Tensile test results demonstrated that addition of B4C facilitated improving the tensile strength by refining matrix and providing particle strengthening. Failure tests revealed that the failure type of the composite transferred from interfacial debonding to particle cracking with increasing wear load. The wear rate of the composite was approximately 48% lower than that of aluminum alloy under 60 N load. The friction coefficient of the composite under 60 N load also significantly decreased due to formation of B2O3 and H3BO3 as solid lubricants.

In this paper, the precipitation and dynamic softening behavior of Al–Fe–Zr alloys were investigated by transmission electron microscopy (TEM), electron back scattering diffraction (EBSD), and the precipitation thermodynamics was studied by JmatPro software. Results show that the optimizing temperature of Al3Zr precipitates was 350 °C and the fraction of butterfly-shaped Al3Zr and rod-shaped Al3Fe reached a peak at ~350 °C. With the increase of Zr content, the fraction of Al3Zr increased, whereas its size and morphology had almost no change. The fraction and morphology of Al3Fe showed less variation with Zr content. Dynamic recovery and dynamic recrystallization occurred during extrusion. The two kinds of precipitation particles in aluminum matrix pinned the dislocations and inhibited dynamic recrystallization effectively. As the Zr content went up from 0.1 to 0.4 wt%, the inhibition got stronger and the fraction of recrystallized grains decreased from 44.2% to 86.9%. As a consequence of the dynamic recrystallization suppression, dynamic recovery became the major softening mechanism.

We present a detailed investigation of the crystal structure, magnetism and magneto-caloric performances of RECo2B2C (RE = Gd, Tb and Dy) compounds. All compounds are described with a LuNi2B2C-type crystallographic structure (I4/mmm space group). A second-ordered paramagnetic to ferromagnetic (PM-FM) transition is observed in RECo2B2C compounds around their Curie temperatures (TC) of 17.2, 5.3 and 7.7 K, and induced a considerable magneto-caloric effect (MCE) for GdCo2B2C, TbCo2B2C and DyCo2B2C, respectively. The magneto-caloric performances for RECo2B2C were characterized by the isothermal magnetic entropy ( - Δ S M max ) , temperature averaged entropy change (TEC) with three different temperature lifts (3, 5 and 10 K), and relative cooling power (RCP). The corresponding values of - Δ S M max , TEC (3 K) and RCP under the magnetic field change (ΔH) of 0–5 T, are 10.34 J/kg-K, 10.23 J/kg-K, and 238.1 J/kg for GdCo2B2C, 18.09 J/kg-K, 17.83 J/kg-K, and 438.2 J/kg for TbCo2B2C, as well as 17.79 J/kg-K, 17.72 J/kg-K, and 480.1 J/kg for DyCo2B2C, respectively.

Rare-earth based amorphous alloys with promising glass forming ability (GFA) and considerable magnetocaloric effect (MCE) are extensively exploited for magnetic refrigeration (MR) materials. Here, the GFA, magnetic properties, MCE, and refrigeration performance of RE60Al20Ni20 (RE = Tm, Er, and Ho) amorphous ribbons were investigated. A magnetic phase transition (paramagnetic to ferromagnetic, second-order) with ignorable field and thermal hysteresis was found around TC ∼ 4.4 K for Tm60Al20Ni20, ∼9.5 K for Er60Al20Ni20, and ∼17.9 K for Ho60Al20Ni20. For a field change ΔH = 50 kOe, the MCE parameters of the maximal magnetic entropy change (around their own TC) and relative cooling power are 14.1 J/kg K and 235 J/kg for Tm60Al20Ni20, 14.3 J/kg K and 372 J/kg for Er60Al20Ni20, and 12.4 J/kg K and 460 J/kg for Ho60Al20Ni20. In addition, the temperature averaged entropy change at ΔTlift (temperature span) of 2 K and 5 K is investigated, very close values and similar field dependence with magnetic entropy change indicating that RE60Al20Ni20 (RE = Tm, Er, and Ho) has potential applications in cryogenic magnetic refrigeration.

In this research, the effect of several heat treatments on the microstructure and microhardness of TC4 (Ti6Al4V) titanium alloy processed by selective laser melting (SLM) is studied. The results showed that the original acicular martensite &alpha, &prime, phase in the TC4 alloy formed by SLM is converted into a lamellar mixture of &alpha, + &beta, for heat treatment temperatures below the critical temperature (T0 at approximately 893 &deg, C). With the increase of heat treatment temperature, the size of the lamellar mixture structure inside of the TC4 part gradually grows. When the heat treatment temperature is above T0, because the cooling rate is relatively steep, the &beta, phase recrystallization transforms into a compact secondary &alpha, phase, and a basketweave structure can be found because the primary &alpha, phase develop and connect or cross each other with different orientations. The residence time for TC4 SLM parts when the treatment temperature is below the critical temperature has little influence: both the &alpha, phase and the &beta, phase will tend to coarsen but hinder each other, thereby limiting grain growth. The microhardness gradually decreases with increasing temperature when the TC4 SLM part is treated below the critical temperature. Conversely, the microhardness increases significantly with increasing temperature when the TC4 SLM part is treated above the critical temperature.

Semisolid slurry of A356 aluminum alloy was prepared by Self-Inoculation Method, and the secondary solidification behavior during rheo-diecasting forming process was researched. The results indicate that the component with non-dendritic and uniformly distributed microstructures can be produced by Rheo-Diecasting (RDC) process (combining Self-inoculation Method (SIM) with High Pressure Die Casting (HPDC)). The isothermal holding time of the slurry has large effect on primary particles, but has little effect on secondary particles. Growth rate of the primary particles in the isothermal holding process conforms to the dynamic equation of Dt3 − D03 = Kt. The suitable holding time for rheo-diecasting of A356 aluminum alloy is 3 min. During filling process, the nucleation occurs throughout the entire remaining liquid, and nuclei grow stably into globular particles with the limited grain size of 6.5μm firstly, then both α1 and α2 particles appear unstable growth phenomenon due to the existence of constitutional undercooling. The average particle sizes and shape factors of both α1 and α2 are decreasing with the increase of filling distance due to different cooling rate in different positions. The growth rate of the eutectic in RDC is 4 times faster than HPDC, which is mainly due to the limitation of α2 particles in RDC process. The average eutectic spacings are decreasing with the increase of filling distance.

The solidification and tensile deformation behaviors of rheo-cast AZ91-Sn alloys were revealed to study the effects of Sn alloying on improvement of AZ91 alloy&rsquo, s mechanical properties. Two kinds of Mg17Al12 phases precipitated from the supersaturated magnesium matrix during rheo-solidification were observed: coarse discontinuous precipitates (DP) at grain boundaries and small-sized continuous precipitates (CP) inside grains. With increasing Sn content, the amount of Mg17Al12 phases was increased whilst the amount of Al atoms in the matrix was decreased. Due to the higher melting point of Mg2Sn than Mg17Al12, Mg2Sn precipitated earlier from the melt, and therefore provided heterogeneous nuclei for Mg17Al12 during the eutectic reaction. Due to grain refinement and solid solution strengthening, AZ91-2.4Sn (mass%) gained 52% increase in tensile strength and 93% increase in elongation compared with pure AZ91 alloy. The higher-density twins and microcracks induced by Sn alloying relaxed stress concentration during plastic deformation, so the fracture mode was transformed from cleavage fracture of pure AZ91 alloy to ductile fracture of AZ91-Sn alloys.

The Er-based compound Er4CoCd was synthesized successfully and its structural, magnetic together with magnetocaloric properties were investigated in detail. The Er4CoCd crystallized in a Gd4RhIn-type structure with the space group of F 4 ¯ 3 m , which was confirmed by Rietveld refinement. A ferromagnetic transition was observed around its Curie temperature (TC) of 12.5 K accompanied by a large magnetocaloric effect (MCE). The performance of MCE for Er4CoCd was evaluated by the isothermal maximal magnetic entropy (- Δ S M max ) , the temperature averaged entropy change (TEC) at 10 K temperature lift [TEC (10 K)], and the relative cooling power (RCP). The values of - Δ S M max , TEC (10 K), and RCP of Er4CoCd are 20.4 J/kg K, 19.2 J/kg K, and 503 J/kg under the magnetic field change (ΔH) of 0–5 T, respectively.

A novel method, powder thixoforming, for net-shape forming of the particle-reinforced Aluminum matrix composites in semi-solid state has been proposed based on powder metallurgy combining with thixoforming technology. The microstructural evolution and phase transformations have been investigated during partial remelting of the 2024 bulk alloy, prepared by cold pressing of atomized alloy powders to clarify the mechanisms of how the consolidated powders evolve into small and spheroidal primary particles available for thixoforming. The effect of heating temperature on the resulting semisolid microstructure has also been discussed. The results indicate that the microstructural evolution includes three stages—the initial rapid coarsening of the fine grains within the powders, the formation of continuous liquid layer on the primary particle surface (the original powder), and the final coarsening—that result from the phase transformations of θ→α, α→L, and α→L and L→α, respectively. The coarsening rate of the primary particles is low, and one original powder always evolves into one spheroidal particle with a continuous liquid layer surface. Properly raising the heating temperature is beneficial for obtaining an ideal semisolid microstructure.

A self-designed test machine of continuously semisolid extending extrusion was made to produce the flat bar of A2017 alloy. The slurry of A2017 alloy with spherical or elliptical structures was obtained. During manufacturing semisolid A2017 alloy by the proposed process, the spherical grain was formed with the application of the large force provided by the rough roll. By controlling the casting temperature, the products of A2017 alloy with fine surfaces and rectangular transections of 14 mm×25 mm were produced. The microstructure of the product is fine with the stripped appearance. The fracture strength and elongation of the product are increased by 100 MPa and 29%, respectively.

Using NH_3·H_2O and NH4HCO3 blended solution as a complex precipitation agent, (Y,Gd)_2O_3:Eu~(3+) nano-particles were synthesized by co-precipitation reaction.XRD and SEM were applied to analyze the crystallization and morphology of the sample.The thermal decomposition curves of samples were analysed by TG-DTA at different heating rates.Results showed that under the conditions of pH=10 and reverse titration,the change process of(Y,Gd)_2O_3:Eu~(3+) precursors is divided into three steps.The apparent activation energy of each step was calculated by using the Doyle-Ozawa and Kissinger methods.The calculated results are 191.54,557.05 and 236.58 kJ-mol~(-1). The dynamic equations have been also established.The activation energy of(Y,Gd)_2O_3:Eu~(3+)grain growth is 35.58 kJ-mol~(-1),indicating that grain growing is primarily controlled by interfacial reaction during process of preparation.