Abstract:A novel severe plastic deformation (SPD) method, entitled Equal Channel Angular Expansion Extrusion with Spherical Cavity (ECAEE-SC) was introduced based on a modification of the conventional Equal Channel Angular Extrusion (ECAE) process. By integrating expansion, shear and extrusion deformations in a single extrusion pass, ECAEE-SC process could induce larger accumulated strains into the billet, resulting in the significant grain refinement and the associated properties improvement. In the present study, commercially pure aluminum (Al-1060) was subjected to one pass of ECAEE-SC process at room temperature, and two passes of ECAE process were also conducted for comparison. The microstructure, Vickers hardness, tensile properties and wear properties of processed material were investigated. The results showed that after one pass of ECAEE-SC process, the grains of ECAEE-SC processed aluminum were greatly refined with a typically elongated microstructure due to the high level of strains induced in the material. The hardness and tensile strength of ECAEE-SC processed material were increased with a significantly growth almost 92.6% and 91.8% than the initial material, respectively. These improvements were considerately higher than that achieved by two passes of ECAE process. Moreover, the wear resistance of ECAEE-SC processed material was also enhanced. The worn surface morphology of ECAEE-SC processed sample represented the minimum width and depth of the wear scars, indicating that the wear mechanism could be dominated by abrasive wear.

Abstract:Effect of Cu content on microstructure and properties of Al-2.5 Mg-x Cu-0.2 Si alloys are investigated in this paper. The microhardness of the alloy with Cu addition has an obvious rapid hardening due to the clustering of Cu and Mg at the early stage of aging. With further aging, the microhardness of the alloy increases again and reaches an obvious second peak due to the formation of S’ phase and GPB zone. The increasing amount of Cu content would result a significant increase in tensile strength and yield strength while its elongation and intergranular corrosion performance reduces. With the increase of Cu content, the intergranular corrosion performance of the alloy becomes worse. The alloy would have a reasonably well corrosion performance when the Cu content is less than 1.1%, however there will be a significant reduction when the alloy in containing 2.0%Cu. Based on these results, the alloy containing 1.1% Cu would have better mechanical properties and corrosion resistance.

Abstract:A356 alloy was processed by semi - solid squeeze casting followed by solution treatment at 540℃. With increasing solution time, Mg and Si elements dissolved into the matrix and led to solid solution strengthening. Tensile strength, elongation and hardness peaked at 6 h and then decreased during solution treatment. Aging treatment at 180℃ for different time was carried out after solution treatment. With increasing aging time, the fine spherical Mg2Si phases precipitated in the A356 alloy matrix, which were ca. 2 μm in size. The optimum heat treatment process was solid solution at 540℃ for 6 h followed by aging at 180℃ for 4 h. After solution and aging treatment, tensile strength and elongation reached 336 MPa and 6.9%, respectively. Hardness value reached 124 HV after heat treatment, which was 106.7% higher than the cast alloy.

Abstract:The hybrid structures of metal-composites have been widely used in the field of aerospace, marine and vehicle industry due to the advantages of high specific modulus and high specific strength of aluminum alloy and resin matrix composites. Therefore, the joining technology between metal and composites as one of the crucial problems in these industries has been paid more attention. In this paper, the connection mechanism and influencing factors of the joining processes of resin matrix composites and aluminum alloy are reviewed. At present, bolt connection, rivet connection, adhesive bonding, injection molded direct joining and welding are studied for the connecting between aluminum alloy and resin matrix composites. The processes of bolt connection and rivet connection are simple, however, the stress concentration is easy to produce around the hole. The cost of adhesive bonding is low, but the anti-impact and anti-stripping strength of the interface is low. The production cycle in the process of injection molding direct joining is short, but the strength of the joint is also low. The degree of automation in the welding technology is high, however, the required equipment is expensive. Finally, the development direction of joining technology between aluminum alloy and resin matrix composites that can obtain the joints with high performance and high reliability is pointed out according to the current research results.

Abstract:Mandatory repair welding for production of structural parts easily causes problems to the reliability of welded joints due to the resultant extra thermal cycle. The evolution of corrosion resistance of repair welded joint between 7N01 aluminum alloy in T5 and T4 state by metal inert gas welding process was investigated. The results reveal that repair welding deteriorated the corrosion resistance of weldment, especially of the heat-affected zone. The main reason for the change in corrosion resistance of repair weldment could be related to the transformation of precipitates and diffusion of Zn from the matrix to grain boundaries caused by the extra thermal cycles.

Abstract:The precipitation microstructure and mechanical properties of as-cast 3104 alloys with different Zr additions was investigated. The results showed that the grain size of alloy decreases with the increase of Zr content, and it has the smallest grain (20μm) when the mass fraction of Zr (Zr wt%) was greater than or equal to 0.25%. Meanwhile, the grain shape changes from feathery to equiaxed. Furthermore, Zr can improve the distribution of Si and Mn elements in the alloy by forming Si phase and other intermetallic compounds. Vickers hardness analysis showed that the addition of Zr will reduce the hardness of Al-Mn-Fe 3104 alloy. Moreover, according to the results of tensile test, tensile strength and the elongation of the cast alloy are increase with Zr content increase until Zr wt% was 0.25%. The proper content of Zr plays a role of pinning dislocation and preventing slip, which improves strength and toughness of the alloys.

Abstract:The review summarized the relationship between multi-scale second phase particles and properties of Al-Zn-Mg-Cu alloys by reviewing related literatures and works done by authors’ group. Multi-scale second phase particles contain micro-scale intermetallic particles, submicro-scale dispersoids, nano-scale inter-granular precipitates and nano-scale intra-granular precipitates. The related properties mainly refer to strength, fracture toughness and corrosion resistance. it is concluded that, in Al-Zn-Mg-Cu alloys, intermetallic particles dominate fracture toughness and corrosion resistance, the dispersoids dominate strength, fracture toughness and corrosion resistance via inhibiting the recrystallization of the matrix, the inter-granular precipitates dominate fracture toughness and corrosion resistance, whereas the intra-granular precipitates dominate strength and fracture toughness. Furthermore, the development of technologies to manipulate multi-scale second phase was reviewed. The aim for the review is to help technical personnel to analyse the possible causes and develop the feasible technologies to synergistically improve the properties of Al-Zn-Mg-Cu alloys.

Abstract:Aluminum matrix composites reinforced with micro-TiB₂ and nano-Al₂O₃ particles were successfully fabricated by combining powder metallurgy and hot rolling with raw materials of fine atomized aluminum powders and TiB₂ particles. The Al₂O₃/TiB₂/Al composites exhibited a yield strength of 258.7 MPa and an ultimate tensile strength of 279.3 MPa at 25 °C due to the comprehensive strengthening effect of TiB₂ and Al₂O₃ particles. The strengthening effect of TiB₂ particles was significantly weakened with temperature rising to 350 ℃, and the Orowan strengthening mechanism between nano-Al₂O₃ and dislocation made the yield strength and tensile strength of the composite material reach 98.2MPa and 122.5MPa. After annealing at 350 ℃ for 1000h, due to the pinning effect of nano-Al₂O₃ on grain boundaries, the grains growth were suppressed significantly and the strength and hardness did not decrease significantly. The main fracture mechanism of composites changed from brittle TiB₂ particle fracture to interface debonding between TiB₂ and the matrix from room temperature to elevated temperature.

Abstract:IFW method has the potential of being ideal technology to weld dissimilar materials, aluminum and stainless steel were welded by inertia friction, and the morphology, microstructure, interfacial composition and mechanical properties of Al/steel joints were investigated. Results showed that a thin IMC reaction layer was found at the welding interface in the joint, and the IMC was consisted of Al, Fe and high concentration Si. The microstructure of joint contained weld nugget zone, fully dynamic recrystallized zone, thermal mechanically affected zone and heat affected zone. The grain of fully dynamic recrystallized zone (FDRZ) was below 0.1 μm, and the average width of FDRZ in the joint was about 5 μm. The maximum hardness was in the FDRZ, and the maximum value was 395.8 HV in the joint. Tensile strength of joint was influenced by the rotational speed. When the rotational speed was 1100 rpm, the joint reached to the maximum tensile strength of 323 MPa. The high tensile strength reason should be related to the thickness of IMC at the weld interface.

Abstract:Dislocation properties of {110} in Al-Dy intermetallic compound with B2 structure were studied by truncation approximation.The results show that the Burgess vector is <110>, the core width of the directional screw, edge and mixed dislocation should be greater than <100> irection. Their corresponding unstable stratification energy is present γ_us<110> < γ_us<001>. It can be seen that the unstable stratification energy is one of the important factors affecting the dislocation properties of intermetallic compounds with B2 structure. B2-AlDy slip system is <111>. For the dislocation of {110}, except for the dislocation with a dislocation Angle of 54.7°, the elastic strain energy of other dislocation angles is greater than the misfit energy, and their phases are always opposite in the same period.When the dislocation Angle is 54.7°, the misfit energy is greater than the elastic strain energy, and both of them are in phase in the same period. In general, for the {110} plane of B2-AlDy, <100>, <110> and <111> direction of dislocation, with the reduction of dislocation angle (except the <111> direction for the dislocation angle of 54.7°), the total energy and the corresponding stress increase in turn.

Abstract:0.4%Mn element was added into 7A99 alloy by semi-continuous casting in the study. TEM, HRTEM and 3DAP were employed to study the microscopic configuration distribution of Mn element in the cast, homogenization and solution aging of 7A99 alloy. The result shows that Mn element in 7A99 aluminum alloy ingot mainly exists in the form of fishbone shape MgZn₂non-equilibrium eutectic compound containing AlZnMgCuMn at grain boundary. After homogenization treatment, Mn element in 7A99 alloy mainly exists in the form of Al₆Mn phase and intermittent, fine, granular S(Al₂CuMg) second phase containing AlZnMgCuMn at grain boundary. A small part of Al₆Mn precipitated phase is dissolved back to the matrix, so that the size range of residual Al₆Mn precipitated phase is 0.2~1μm in the process of solid solution treatment. Mn element always exists in the form of Al₆Mn precipitated phase which is stable in size and non-coherent with aluminum matrix in the aging process of 120℃. Mn element does not precipitate other new phase during the aging proceed and affect the aging precipitation process of Zn, Mg in 7A99 alloy.

Abstract:The use of high damping Al alloy is of great significance for lightweight components or equipment and shock absorption and noise reduction. However, due to the low intrinsic of Al alloy, it is one of the development directions to improve the damping properties of Al alloy by alloying and introducing high damping second phase. The influence of rare earth La on the microstructure, damping and mechanical properties of cast aluminum alloy containing 4 wt.%Sn is studied. The damping improvement mechanism is discussed from the aspects of La on the morphology and distribution of Sn, and the influence of La on the wetting characteristics of Sn and aluminum alloy matrix. The results show that when the La content is 0.2 wt.%, the grain size of 4 wt.%Sn AlMgMnSi alloy is improved, and the β-Sn from large granular to fine, diffuse distribution.The La content increase to 0.83 wt.%, the grain size becomes larger and the bulk rare earth compounds appear at grain boundary. The addition of La can effectively improve the damping performance of the cast aluminum alloy containing 4 wt.%Sn. When the La addition amount is 0.2 wt.%, the damping property of AlMgMnSi with 4wt.%Sn and ZL102 alloy increase by about 70% and 100%. Respectively, La improves the wettability of β-Sn and aluminum matrix, make the β-Sn diffuse and fine distribution, thus improving the phase interface damping, which is the reason for the high damping performance of the samples.

Abstract:Al-14.4Mg-0.33Sc-0.19Zr aluminium alloy with wide particle size distribution powders (2-46 μm) and high Mg-content was prepared by selective laser melting (SLM). The effects of different process parameters and aging treatment on the processability, microstructure and mechanical properties of SLM-formed Al-Mg-Sc-Zr alloy were systematically studied. Experimental results showed that the high laser power could effectively reduce the influence of fine powders splash on the processability of the samples. The maximum relative density of the sample reached 98.6%. The microstructures of the samples composed of fine equiaxed grains and coarse grains. The increase of Mg content in Al-Mg-Sc-Zr alloy reduced the texture and the content of columnar grains. The micro-hardness first increased and then decreased with the increases of aging temperatures. Both micro-hardness and compression yield strength showed dual-peak phenomenon with the increase of aging time at 350 ℃. The maximum micro-hardness ~ 163±3 HV and compressive yield strength ~ 457±10 MPa appeared for the sample ageing treatment at 350 ℃ for 1 h, with an elongation of 27±3%. After aged the samples at 350 ℃ for a long time, the micro-hardness and compressive yield strength of the sample decreased due to coarsening of the precipitated particles. In this study, the utilization ratio of the powders were efectively improved by increasing the particle size distribution of alloy powders, and SLM-formed high Mg-content Al-Mg-Sc-Zr alloy exhibited good processability and mechanical properties.

Abstract:GLEEBLE-3500 thermal simulation system and EBSD technology were used to study the microstructure evolution of 5083 aluminum alloy under ultra-fast annealing. The effects of rapid heating rate, annealing temperature and cold rolling deformation on the grain size of 5083 aluminum alloy were discussed. The average grain size of 5083 aluminum alloy was refined from 7.43 μm to 4.98 μm with the increase of the heating rate from 25 ℃/s to 500 ℃/s. After ultra-fast annealing (heating rate 500 ℃ / s, holding time 3 s, cooling rate 40 ℃ / s) at different annealing temperatures (350 ℃, 400 ℃, 420 ℃, 450 ℃ and 500 ℃), the grain size of the 80% cold-rolled 5083 aluminum alloy first decreased and then increased. When annealed at 420 ℃, the minimum grain size was 4.82 μm. The grain size of recrystallization was affected by the interaction of boundary migration rate and nucleation rate. During the ultra-fast annealing at 350 ℃ ~ 420 ℃, the nucleation rate increased sharply due to the rapid heating, while the nucleation temperature was low, which makes the grain boundary migration rate smaller, resulting in the grain boundary migration rate less than the nucleation rate, and the recrystallization grain size was refined from 5.23 μm to 4.82 μm; During the ultra-fast annealing at 420 ℃ ~ 500 ℃, the nucleation temperature became higher and the grain boundary migration rate increased rapidly. The grain boundary migration rate was higher than the nucleation rate, which makes the grain coarsening from 4.82 μm to 6.20 μm. 420 ℃ was a critical point for the competition between the grain boundary migration rate and the nucleation rate of 5083 aluminum alloy. After 50%, 60%, 71.4%, 80% and 87.5% cold rolling, 5083 aluminum alloy was heated to 450 ℃ for 3 s at an ultra-rapid heating rate of 500 ℃ / s and cooled at 40 ℃ / s. The average grain sizes were 7.94 μ m, 6.82 μ m, 6.03 μ m, 4.98 μ m and 4.84 μ m, respectively. With the increase of rolling deformation, the grain size decreased, but after the cold rolling reached 80%, the grain size decreased unobviously.

Abstract:The friction stir processing (FSP) was employed to modify 1060 Al surface composites reinforced with Pb particles. The scanning electron microscopy, electron backscatter diffraction, nanoindentation and hardness tester were applied to investigate the microstructure, texture and hardness of Al-Pb surface composites. The results show that the Pb particles are mainly distributed at the bottom of processing area, which is effected by gravity and agitation. In the onion ring structure formed by plastic metal convection, there are Pb-rich zone and deformed Al matrix zone. The Pb particles in the Pb-rich zone play an importent role in grain refinement. A small amount of the new Pb particles (about 100 nm) are distributed in the deformed aluminum matrix. The hardness of Pb-rich zone are significantly higher than that of deformed aluminum matrix. Furthermore, crystallographic texture analysis by electron backscatter diffraction indicates that there are different types of texture in different zone in the processing area. At the bottom of the processing zone, there is a strong Cube texture on SZ-AS. SZ-RS has Cube texture and a small amount of (110)<233> deformation texture, and CSZ has weak Cube texture and {111} texture. At the top, there is a strong Goss texture on AS, but the texture on RS is relatively random.

Abstract:Aluminum alloy has the advantages of low density, light weight, corrosion resistance and high specific strength, so it is the first choice material for structural lightweight design. However, its mechanical properties are greatly affected on the final heat treatment state and deformation conditions of aluminum alloy. Take the 5052-H32 as the research object, the mechanical properties was studied under the condition of different heat treatment parameters by uniaxial tensile test and hardness test, and the influence mechanism of different heat treatment parameters on mechanical properties of 5052 aluminum alloy was analyzed, the results showed that, The deformation resistance of 5052-H32 aluminum alloy can be significantly reduced and its plastic deformation ability can be improved during re-heat treatment. The heating temperature plays a major role in the process of heat treatment, the cooling mode has little influence on the strength and hardness of 5052 aluminum alloy under the reasonable heat treatment temperature and holding time. On this basis, the constitutive model of 5052 aluminum alloy after re-heat treatment was established by johnson-cook model.

Abstract:Al-Li alloys have attracted considerable attention in the key fields of aviation, aerospace, and navigation owing to their high specific strength and stiffness, good corrosion and fatigue resistance. Al-Li alloys have been studied and applied for decades in the United States, Russia and other countries. The researches and applications of Al-Li alloys in our China have also achieved great progress through a number of science and technology projects. However, there is still a certain gap between China and developed countries. Based on the development of Al-Li alloys at home and abroad, alloying techniques, aging precipitation behavior, the strengthening and toughening mechanism of Al-Li alloys are discussed. At the same time, the new processes and heat treatments of Al-Li alloys are summarized. At the end of this paper, the existing problems in the development and application of Al-Li alloys in China are put forward and the development direction of Al-Li alloy is prospected.

Abstract:SiCp/Al composites have excellent properties and are widely used in advanced aerospace equipment. However, due to the great difference in physical and mechanical properties between SiC particles and aluminum alloy, it is easy to be damaged in the process of processing, which seriously affects the accuracy and service performance of SiCp/Al composites products and restricts its engineering application. This paper focuses on the low damage processing technology of SiCp/Al composites, analyzes the related research progress at home and abroad from three aspects: the formation mechanism of processing damage, the influencing factors of processing damage, low damage processing tools and low damage processing technology, summarizes the current research status and shortcomings of low damage processing technology for SiCp/Al composites, and brings forward the development trend and direction.

Abstract:In this study, using spark plasma sintering, an ultrafine porous boron nitride nanofiber-improved WC-ZrO2 composite was prepared. The obtained composites displayed superior properties in terms of hardness and fracture toughness. In particular, the Young’s modulus value increased but did not follow the rule of mixtures for most of ceramics-based composites (up to 692 GPa, close to 700 GPa of pure WC).

Abstract:Low-temperature slow rate extrusion (LTSRE) and electrical pulse treatment (EPT) were carried out to obtain a bimodal microstructure in AZ91 Mg alloy, which consisted of coarse un-recrystallized grains of about 20-60μm and fine recrystallized grains of around 200nm. The bimodal grains can be contributed to the inhomogeneous deformation under LTSRE and the acceleration effect of the static recrystallization of the deformed AZ91 magnesium alloy under EPT. In addition, the growth of the recrystallized grains was effectively restrained due to the notably lower recrystallization temperature and shorter processing time compared with the conventional static recrystallization by heat treatment. Meanwhile, abundant Mg₁₇Al₁₂ phase with an average size of 200nm and regular shapes precipitated during EPT. Consequently, the exceptional yield strength of 463MPa and ultimate tensile strength of 527MPa were acquired in the bimodal AZ91 alloy, which can be primarily attributed to the bimodal microstructure as well as the combined effect of fine grain strengthening, precipitation strengthening and work hardening.

Abstract:In order to study the effect of crystal orientation on the nano-cutting process of single crystal γ-TiAl alloy, molecular dynamic numerical methods were used to analyze and discuss the cutting force, cutting temperature, material removal and lattice structure changes of different cutting crystal directions, revealing different mechanism of crystal orientation on nano-cutting quality of single crystal γ-TiAl alloy. The results show that during the nano-cutting process, the cutting force, cutting temperature, material removal and lattice structure change with the change of crystal surface and crystal direction. When the (010) crystal plane is selected as the cutting plane, the cutting force is smaller, the cutting heat generated is less, the surface processing quality of the γ-TiAl alloy is better, and the lattice structure is changed less. The workpiece in the direction of (010) [100] cutting crystals produces less cutting heat and is the easiest to cut, with the least transformation of lattice structure and the best surface processing quality of the γ-TiAl alloy

Abstract:In the present work, in order to obtain the magnesium matrix composites with good mechanical properties, the semi-solid billet 10μm 15wt.%SiC/AZ91D was prepared using the near-liquidus heat-holding method and later semi-solid extruded to get the magnesium matrix composites. Next, 24h of solution treatment at 415oC (T4) was conducted, followed by 8h of further aging treatment at 220oC (T6). The results show that, with the progress of solution and aging treatments, Mg17Al12 phases at the grain boundary were dissolved, and secondary-precipitated in grains with layered and spheroidized gradually. The magnesium matrix composites 15wt.% SiC/AZ91D after T6 treatment showed better integrated mechanical properties when compared with those before, with tensile strength, yield strength, elongation, and hardness reaching 242MPa, 204MPa, 2.3% and 132.26HV, respectively.

Abstract:Stress relaxation is a critical stage for some accurate forming processes, such as hot sizing. In the relaxation stage, the part keeps the deformed status, meanwhile the internal stress decreases as time increases. Material characterization and constitutive modeling for the stress relaxation behavior are the fundamental issues for these forming processes. The present work focus on the material characterization and validation of relaxation behavior of Ti-4Al-1.5Mn alloy at high temperature. Firstly, constitutive models for the relaxation behavior at 500℃, 600℃ and 700℃ are established based on the stress relaxation tests. Further, the models are applied to finite element software ABAQUS to simulate the influence of stress relaxation on the springback after V-bending. The results show that the stress relaxation is controlled by temperature and relaxation time. The relaxation process can be divided into two stages. In the first stage, the stress decreases fast. In the second stage, the stress decreases slowly. Finally the residual stress decreases to a limit value, which is defined as relaxation limit. Both hyperbolic sine and time hardening model can predict the variation of stress relaxation. The predicted springback shows promising agreement with the corresponding experimental observations. Hyperbolic sine model is more reliable than the time hardening model. The study is of guiding significance for the design of precise forming process by means of relaxation process.

Abstract:Hot deformation behavior and microstructural evolution of the as-cast Mg-3Sn-1Mn-1La alloy were investigated by isothermal compression at temperature of 200-450℃ and strain rate of 0.001-1.0s-1. The flow stress increases obviously with decreasing temperature and increasing strain rate. The recrystallized grain size increases with increasing temperature and decreasing strain rate. At lower deformation temperatures, continuous dynamic recrystallization is the main mechanism of DRX. However, discontinuous dynamic recrystallization becomes the predominant operating mechanism of DRX at high deformation temperature. The effects of friction and deformation heating on flow stress were analyzed and corrected. The results show that deformation heating has a significant influence on the flow stress at higher strain rates and lower temperatures, while the frictional effect is slight. Based on the experimental results, a strain-compensated Arrhenius-type equation was developed. Comparison of the experimental data with the calculated flow stress indicates that the developed constitutive equations can adequately describe the hot deformation behavior of the experimental alloy.

Abstract:A newly Ti-doped In2O3 rotary target was used to prepare transparent conductive oxide (TCO) films for amorphous/crystalline silicon heterojunction solar cells. The changes in electrical and optical properties of TCO films were investigated based on T100 thin films deposited under various O2 content mixture and ITO reference. A columnar structure was observed and exhibited high quality on optical performance. Maximum mobility of 75.6 cm2 V?1s?1 was observed in Ti-doped In2O3 films. Compared to the ITO films, it was verified that T100 material can support enhancement of 0.26% in cell conversion efficiency based on HJT production line, mainly benefit from their excellent electrical transport properties, as well as the high transparency.

Abstract:The microstructure, tensile properties, Charpy impact toughness and corrosion resistance of Ti-6Al-3Nb-2Zr-1Mo-xTa (x=0, 0.5, 1.0, 3.0 and 5.0) alloys were investigated. The results indicated that, except for the lamellar structure Ti-6Al-3Nb-2Zr-1Mo-5Ta alloy, the bimodal structure was obtained in Ti-6Al-3Nb-2Zr-1Mo-xTa (x=0, 0.5, 1.0 and 3.0) after hot deformation during α+β region. The results of XRD pattern and selected area electron diffraction indicate that, no new phase was indentified after adding Ta element although the XRD peaks of both α and β phases shift toward the low angle side as the increasing of Ta content. For the bimodal structure Ti-6Al-3Nb-Zr-1M0-xTa alloy, the yield strength (YS), ultimate tensile strength (UTS) and microhardness increase due to the increasing of molybdenum equivalent (Mo[eq]). The impact absorb energy dependence on the Ta content is opposite to YS, UTS and microhardness, and their value are consistent with the area of shear lip region on the impact fracture surface. when the Ta content is more than 1.0 wt%, the resistance to corrosion of Ti-6Al-3Nb-2Zr-1Mo-xTa alloys decrease due to the increasing of standard balancing potential difference between α and β phase as the Ta content increasing. After potentiodynamic polarization tests, the samples surface area are covered with lots of corrosion pits, which are mainly distributed in the αp grain interior and α/β interface. Combining YS, impact toughness and corrosion performance, Ti-6Al-3Nb-2Zr-1Mo-1Ta alloy exhibits the best compatibility, suggests its promising potential for marine applications.

Abstract:A novel Fe-28Mn-10Al-C-0.5Nb low density steel containing 0.5wt% Nb for automobile was developed, aiming to study the existence of Nb and the effect of Nb addition on the structure and mechanical properties of austenitic Fe-Mn-Al-C low-density steel. The results show that, Nb is distributed in austenite grains and grain boundaries in Fe-28Mn-10Al-C-0.5Nb low density steel in the form of NbC. With the addition of Nb, the average austenite grain size in Fe-Mn-Al-C low density steel is refined from 39.49μm to 13.67μm，and the formation of annealing twins is also suppressed by the addition of Nb. With the addition of Nb, the yield strength and ultimate tensile strength of Fe-28Mn-10Al-C low density steel increased by 64-170 MPa to the other, and the elongation after fracture increased by 11%, revealing an excellent balance of strength and ductility. This is due to the precipitation strengthening of NbC precipitates and fine grain strengthening of austenite. Precision strengthening plays main role to the increase of yield strength of Nb-added low density steel.

Abstract:Pure niobium girth weld seam is one of the most common structures in the process of superconducting cavity fabrication. However, the circumferential molten pool behaviour in electron beam welding (EBW) has been seldom studied. In this paper, a three-dimensional model, which is combined with the VOF model, is established to study the dynamic behaviour of circumferential molten pool in electron beam welding of 2 mm niobium plate. The influences of recoil pressure, surface tension and gravity are taken into account during the simulation process. The temperature field and flow field of the circumferential molten pool are calculated, the typical positions in the molten pool are analyzed, and the characteristics of the circumferential molten pool are summarized. During partial penetration EBW, the simulation results show that there is no obvious difference in keyhole evolution between flat welding and girth welding due to the supporting effect of the unfused base metal on the molten pool. After entering the full penetration stage, the tail of the molten pool extends rapidly under the influence of the Marangoni effect and gravity. In addition, the numerical result is in good agreement with the experimental data, which verifies the rationality of the mathematical model.

Abstract:Tungsten carbide (WC) is increasingly used in high-temperature power equipment. The brittleness and high density of WC limit its wider use. Metal atom doping is a method to improve the performance of WC. The generalized gradient based on the first principle is used as the approximate exchange correlation function. The elastic, electron and X-ray absorption characteristics of A0.25W0.75C (A is Ti, V, Cr, Mn, Co and Ni) were studied. According to the numerical analysis, the B/G value of Ti0.25W0.75c (B is the volume modulus, G is the shear modulus) is 1.869, the material is the modified ductile material, and the others are brittle materials. The brittleness of WC decreases with the doping of 25% V and Co atoms, and brittleness increases with the doping of 25% Cr, Mn and Ni atoms. After doping, the range of density of state decreases, the value of Fermi level increases, and the metallicity of the compounds increases. Among them, Mn0.25W0.75C has the strongest metallicity. The X-ray absorption spectrum shifts blue after doping, and there is an absorption band in a soft X-ray band. The strong absorption peaks of doping Cr, V, and Ti appears in the 15.74～22.25 nm band. The results are helpful to the experimental and application study of WC compounds with plasticity and low density.

Abstract:The single-pass isothermal compression test of BT25 titanium alloy was carried out by Gleeble-3500 thermal simulation machine. Najafizadeh-Jonas model of working hardening rate and Cingara-McQueen model of flow stress were used to study the critical conditions of dynamic recrystallization under the conditions of deformation temperature 1040 ~ 1100 ℃, strain rate 0.001 ~ 1 s_^-1 and maximum height reduction of 60%. The true stress-true strain curve were analyzed, and the critical strain model was established. At the same time, JMAK dynamic recrystallization kinetic equation was constructed by calculating material parameters and linear regression method. A numerical simulation model was developed to simulate the dynamic recrystallization behavior of BT25 titanium alloy during thermal deformation. The results show: The flow stress is sensitive to the strain rate and deformation temperature. High temperature and low strain rate are favorable for DRX. The prediction error of the finite element model for predicting DRX volume fraction is less than 10%. The results show that the model has a good prediction ability and provides an effective tool for predicting plastic deformation and microstructure in industrial production.

Abstract:Two different heat treatment processes, vacuum high temperature and vacuum high frequency, are used to pre-treat cerium-tungsten electrodes for high-power pulsed xenon lamps. The metallographic morphology and the concentration-depth distribution and the evolution of valence state of cerium element of the cerium-tungsten electrodes were studied by some analysis and testing methods, like metallographic microscope, Electron probe micro-analyzer(EPMA) and X-ray photoelectron spectroscopy (XPS). The concentration-depth distribution of the elements was studied to analyze the behavior mechanism of the diffusion and enrichment of the cerium element in the electrode sample, and the effect of the heat treatment process of the cerium-tungsten electrode on the emission performance after lamp manufacture was clarified.

Abstract:The difference of the transverse and longitudinal impact toughness of TC18 large-scale forging rods and its microstructural relationships have been systematically investigated in this study. Two types of impact samples, i.e., the C-L ones and the C-R ones, were machined from the head, middle and tail positions of the forging rods for Charpy impact testing. It is found that the impact toughness of the C-L samples is always higher than that of the C-R samples. The instrumented impact test further reveals that the ability to resist crack initiation is a key factor affecting impact toughness, whilst crack initiation energy of the C-L samples is significantly greater than that of the CR samples. Meanwhile, impact fracture observation manifests that cracks initiate in the form of micro-void coalescence, and mainly originate from the strong-hard phase (such as the α-phase of the grain boundary) near the notch of the samples. For the C-L samples, the elongated direction of the forging microstructure is parallel to the fracture direction, while it is perpendicular to the propagation direction after the micro-void initiation. The crack is thus difficult to grow to the critical size for unstable propagation, which results in the high consumed energy for crack initiation; for the C-R siblings, however, the elongated direction of the primary α-phase including grain boundary α-phase is parallel to the direction of crack initiation, and the cracks easily grow directly to the critical size along the strong-hard phase for unstable propagation, which causes a lower impact toughness in the samples.

Abstract:In order to explore the influence of different electrolyte flow states on mask-less localized electrodeposition, the nickel column was detected by stereoscopic microscopy and scanning electron microscopy, and the average deposition diameter and rate were calculated. On the basis of experiments, the effects of pulse voltage amplitude and electrolyte flow states on average deposition diameter, average deposition rate and surface morphology of micro nickel column were studied by means of control variable method. The research shows that the higher pulse voltage amplitude leads to the greater deposition rate and rougher surface of the micro-nickel column. the average deposition diameter and rate will change with the change of electrolyte flow states, and the deposition rate will increase with the increase of the flow rate of the electrolyte. The increase of the voltage in droplet, droplet and micro-jet will lead to the increase of the deposition diameter of the micro-nickel column. In the impinging jet state, the diameter of the micro-nickel column will first increase and then decrease with the increase of the voltage. At the same time, the tip of the nickel column is obviously tapered and there are "burrs" around the nickel column. The surface of nickel column varies with the velocity of each injection mode. The surface of nickel column is denser under the condition of high velocity injection.

Abstract:Nanocrystalline ZnO is widely used in the field of microelectronics, and its thermal conductivity has an important effect on the performance of electronic devices. In order to explore the effect of grain boundary geometry on the thermal conduction of nanocrystalline ZnO,,the grain boundary geometries were abstracted into several typical structures. On this basis, the calculation of grain boundary surface roughness and the effect of phonons incident angle on specular reflectance were discussed, and the calculation model of grain boundary specular reflectance was improved. PhonTS software was used to solve the boltzmann transport equation iteratively to obtain the perfect lattice thermal conductivity of nanocrystalline ZnO. The thermal conductivity of nanocrystal ZnO was calculated based on the molecular dynamics theory, and effects of specular reflectance, phonon incidence angle and grain size on the thermal conductivity were analyzed. The results showed that: (1) the decreases of grain boundary surface roughness or the increases of phonon incidence angle will increase the specular reflectance of grain boundary; (2) phonons specular reflectance at grain boundary will not generate thermal resistance, and the thermal conductivity of nanocrystalline materials increases with the increase of specular reflectance; (3) the thermal conductivity of nanocrystalline ZnO shows a strong size effect, which decreases with the increasing of grain size.

Abstract:Aiming at the outer and edge collapse of the variable radius cylinder by laser cladding forming, the decrease of the mechanical properties caused by the thermal accumulation effect. The optimized path and process of FeCrNiCu alloy cylinder by pulsed laser forming was put forward, the direct cladding forming of the variable radius cylinder structure was realized, the good structure and mechanical properties of the structure were verified. The experiment results show that, the top of the forming layer is fine and dense equiaxed crystal structure, the middle of the forming part is composed of dendrites with a certain directional growth trend, the bottom of the forming part is composed of cellular crystal, and there are granular Cr7C3 enhanced precipitated in and between the crystals. The highest microhardness of the coating is 675HV0.1, and the microhardness of the coating is mainly distributed in 554 ~ 576HV0.1. The maximum longitudinal tensile strength of the forming layer is 1070 MPa, and the tensile strength is range from 1010 to 1070 MPa, the maximum transverse tensile strength of the forming layer is 860 MPa, and the tensile strength is range from 780 to 960 MPa. The impact toughness distribution of the coating is 511 ~ 727.5 kJ?m-2, the excellent mechanical properties of the forming part were verified by the relevant mechanical experiments.

Abstract:Mn65-Cu23.75-Zn3-Al3-Ni3-Fe2-Ce0.05 (at%) alloy was prepared by vacuum induction melting method, and then rolled at 400 ℃ with a height reduction of 40% and further annealed at 800 .℃ for 5 h. The alloy samples were solid solution and semi-solid solution treated at 850 ℃ and 950~1050 ℃ for 20 min respectively, and then aged at 430 ℃ for 0~16 h. The effects of semi-solid solution temperature and aging time on the microstructure, damping capacity and mechanical properties of Mn-Cu alloys were studied. The results show that the microstructure of solid solution treated alloy is composed of a single γ-MnCu phase, while that of the semi-solid solution treated one comprises Mn-rich and Mn-poor γ-MnCu phases. The amount of Mn-poor γ-MnCu phase gradually rises with increase in semi-solid solution temperature. The damping capacity of the alloy firstly increases and then deceases with increasing the aging time. Under optimal aging conditions,,the damping capacity of the alloy is improved at a relatively lower semi-solid solution temperature while degraded at a relatively higher semi-solid solution one. The tensile properties of the alloys semi-solid solution treated at 950 and 1000 ℃ are improved compared to the alloy solid solution treated at 850 ℃ (especially, the product of strength and ductility of S950 alloy is 70% higher than that of S850 one). However, the product of strength and ductility of the alloy decreases instead with further increase in semi-solid solution temperature.

Abstract:The composite refractory crucible using the fused BaZrO3 and Y2O3 was fabricated after sintering at 1650℃ for 24h, then induction melting of TiAl alloy was carried out in the crucible. By using the X-ray diffraction, scanning electron microscope combined with the energy disperse spectroscopy, inductively coupled plasma atomic emission pectrometry and O/N analyzer, the phase composition and microstructure for the composite refractory are investigated as well as the interaction between the composite crucible and TiAl alloy melt. Results reveal that the composite crucible is consisted of Y doped BaZrO3 and Y2O3(ZrO2) phases, and the introduce of Y2O3 is help to the improvement of fused BaZrO3 refractory. Dissolution-erosion is the main responsible for the interaction between the refractory and TiAl alloy melt, however, the Al2O3 in the melt reacts with the BaO leading to the generation of reactant BaAl2O4, which attaches to the inner wall of the crucible. The oxygen concentration for the prepared TiAl alloy ingot is about 0.0986wt.%, which is consistent with the calculated value for the TiAl alloy. It is also met criteria for the industrial TiAl alloy ingot, which indicates that the BaZrO3/Y2O3 composite refractory is the candidate for induction melting of TiAl alloys.

Abstract:In this paper, one step method was investigated to prepare La0.4Sr0.6Co0.2Fe0.7Nb0.1O3-δ-Gd0.2Ce0.8O2-δ (LSCFN-CGO) compound symmetrical electrode, La0.8Sr0.2Ga0.83Mg0.17O3-δ (LSGM) was used as electrolyte and symmetrical cells with a con?guration of LSCFN-CGO||LSGM||LSCFN-CGO were successfully fabricated. Phase-analysis and electrode microstructure of LSCFN-CGO were examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). LSCFN-CGO was identified to be pure phase and perovskite structured LSCFN chemically compatible with ?uorite structured CGO. Using H2 (3% H2O) and C3H8 (3% H2O) as fuel for the cell, the maximum power densities were 980 mW/cm2 and 869 mW/cm2 at 850 ℃. Moreover, the long-term stability of the cell is demonstrated to be stable for 420 h under constant current of 0.3 A/cm2 using C3H8 (3% H2O) as fuel, 8 redox cycles were carried out, and the symmetrical electrode had ideal redox regeneration ability under carbon-based fuel. Results show that, one step method is a facile and optimized electrode fabrication procedure and owns promising application prospects.

Abstract:As the most promising plasma facing materials (PFMs),potassium doped tungsten alloy have exhibited excellent high temperature mechanical properties. In order to evaluate the hydrogen isotope residence in WK alloy,the pure W and the WK alloy with 82 ppm potassium doping were prepared by spark plasma sintering(SPS). After deuterium was introduced into potassium doped tungsten alloy by gas-phase thermal charge, thermal desorption spectra(TDS) were obtained with different heating rates. The results show that deuterium released gradually at 600 K～1200 K. And after doping K, the activation energy of thermal desorption of deuterium reduced from 0.86 eV to 0.68 eV; The retention of deuterium in tungsten sample is less than 1 appm and it is enhanced with doping K,but still lower than that of commercial pure W

Abstract:Directed laser deposition is a significant laser additive manufacturing technology, and it has been widely utilized in the field of preparing high melting point melt growth oxide ceramics. Due to inadequate understanding of the influence law and internal mechanism of laser additive manufacturing ceramics under the action of different laser energy, the wider application of this technology is limited. In this study, the effects of laser energy density on the porosity/density, microstructure, and mechanical properties of directed laser deposition melt growth mullite ceramics were investigated. The results show that the mullite ceramic samples prepared with lower laser energy density (15 J/mm2) have large pores distributed on the edges, making the porosity of the specimen higher. The sample surface has serious sticky powder, which is related to the high scanning speed and the high viscosity of the silicate melt. The ceramic samples with a smooth surface and smaller mullite grain size were prepared by higher laser energy density (15 J/mm2). However, due to the high energy input into the molten pool per unit time, the pores generated by the evaporation of the powder are too late to escape from the molten pool, resulting in larger pores in the core of the sample, deteriorating the mechanical properties of the samples. The mullite ceramic samples with a relatively smooth surface, low porosity, and high mechanical properties can be obtained when the laser energy density is 45 J/mm2. The results of this study provide theoretical guidance and technical support for the rational selection of process conditions in the process of manufacturing high-performance ceramics with directed laser additive manufacturing.

Abstract:In this paper, the microstructure of Co90Zr7Ta3 ternary alloy and the effect of microstructure on the PTF (pass through flux) were studied by means of metallographic observation, XRD analysis and PTF measurement. The influence of thermo mechanical treatment on the permeability was obtained by analyzing the structure and PTF of the material. The results show that the ternary alloy of Co90Zr7Ta3 prepared by vacuum melting mainly contains the precipitates of Co matrix and dendrite structure of (Co,Ta)11Zr2. After rolling and heat treatment, the dendrite structure in the alloy was broken to form dispersed precipitates. At the same time, the fcc phase in Co matrix is transformed into hcp phase, and the permeability of the target is improved by increasing the orientation of (0001) in hcp phase.

Abstract:High-purity and density Sm1-2xEuxBaxB6（x=0.1, 0.2, 0.3）polycrystals were prepared by using a boron/carbonthermal reduction-hot pressing sintering (BCTR&HP) integrated process. The effect of Eu&Ba doping the SmB6 matrix on the structure, mechanical and electrical properties of Sm1-2xEuxBaxB6 bulks were investigated systematically. The results show that the Sm1-2xEuxBaxB6 polycrystals produced by BCTR&HP provide a simple cubic (CsCl type) single-phase structure. As the doping amount of Eu&Ba increased, the lattice constant increases, which contributes to the enhancement of mechanical properties and the decrease of resistivity. The thermionic emission performance results show that the Eu&Ba doping can improve the emission characteristics of SmB6 cathode, and the emission current density and zero-field current density of Sm0.4Eu0.3Ba0.3B6 cathode are 35.1 mA.cm-2 and 21.4 mA.cm-2 under the applied voltage of 1 kV at 1773 K, respectively. Meanwhile, the average effective work function is 3.6 eV from 1523 to 1773 K, and it can be used as a "direct heating" cathode benefited by its inherent high resistivity, which simplifies the heater structure and has great application prospects.

Abstract:In order to improve the lifetime of the Lithium-ion battery, Mg-Y co-doped LiCoO2 was prepared by high temperature solid phase synthesis, with Co3O4, Li2CO3, Mg(OH)2 and Y2O3 as raw materials. The structure and morphology were characterized by X-ray diffraction (XRD) and scanning electron microscpoe (SEM). The battery achieved best electrochemical performance when the cathode is doped with 0.10wt% yttrium and 0.20wt% magnesium. The results of electrochemical performance showed that the initial discharge capacity was 212.3 mAh/g at 0.5C, 3.0-4.6V and with the outstanding capacity retention of 96.28% after 50 cycles at 3.0-4.6V. The discharge capacity of co-doped LiCoO2 at 4.0C remained 60.43% of the discharge capacity at 0.2C, while that of Mg only doped LiCoO2 is only 54.92%.

Abstract:Mg-25Sn-xZn alloys were prepared by mechanical alloying and hot-press sintering methods using Mg powders, Sn powders and Zn powders as raw materials. The effects of the Zn content on microstructures and mechanical properties of the Mg-25Sn alloys were studied. The results show that Zn didn"t participate with the alloying reaction in the mechanical alloy process of Mg-25Sn-xZn system, but the introduction of Zn reduced the size of Mg+Mg₂Sn mixture. The Zn in the sintered Mg-25Sn-xZn was completely transformed into MgZn₂ phase except the solution. And with the increase of the Zn content, the size of MgZn₂ phase gradually increased. MgZn₂ phase was preferentially distributed along Mg grain boundary and around Mg₂Sn particle phase. When the Zn addition is 6wt%, the Mg-25Sn alloy exhibited excellent mechanical properties, hardness, yield strength, fracture strength and strain are 1.60GPa, 388MPa, 497MPa and 7.5% respectively.

Abstract:In this paper, the cohesive zone model is used to study the interface damage process of zirconium-titanium-steel clad plate in bonding test, and the interface fracture mode is analyzed by SEM observation. The corrosion resistance of the surface under different heat treatment conditions was studied by orthogonal test, and the effects of holding temperature, holding time and temperature rise and fall rate were analyzed. The results show that the interface damage starts from the inner wall and gradually develops to the whole interface under mode-I loading. The whole interface belongs to brittle fracture, while the transition slope of wave crest and wave trough is mixed fracture. The results of Tafel polarization curves show that the main corrosion mode of zirconium coating is spot corrosion in HCl solution and uniform corrosion in HAC solution. After explosive welding, the corrosion resistance of zirconium composite plate is lower than that of pure zirconium material, and worse corrosion-proof ability will be .obtained under higher temperature and longer holding time.

Abstract:In order to development high quality W/Re alloy targets, pure W and W/Re alloy (with 1wt.%, 5wt.% and 10wt.% content of Re) was fabricated by mechanical mixing, press forming and vacuum sintering. Properties such as relative density, grain size and direction, magnetron sputtering of W/Re alloy were investigated. Relative density of W/Re alloy increased with content of Re addition. And relative density of W/10wt.%Re was high up to 96.6%. EPMA results showed that the purity of W/10wt.%Re alloy target was very high. And grain size of W/10wt.%Re alloy was mainly distributed between 10 μm and 40 μm. The grain size of W/Re alloy was randomly distributed without preferred orientation as shown in EBSD results. And content of small angle grain boundary (< 10 °) of W/10wt.%Re alloy was more than 85%. The grain size of W/Re alloy thin film was gradually refined as deposition pressure of magnetron sputtering increasing. Meanwhile, both surface flatness and thickness of thin film were gradually increased. XRD spectra of thin films showed that (110), (200) and (211) diffraction peaks appeared near 40.5 °, 58.6 ° and 73.5 °, respectively. As the deposition pressure increasing, the intensity of (110) diffraction peaks decreased gradually, while those of (200) diffraction peaks increased gradually.

Abstract:The microstructure of electron beam welded GH4169D alloy was analyzed by optical microscope (OM) and scanning electron microscope (SEM). Micro hardness of fusion zone, heat affected zone (HAZ) and base metal were examined by micro hardness tester. The stress rupture characteristic of electron beam welded GH4169D alloy was researched by stereo microscope (SM) and SEM. The precipitated phases of GH4169D alloy are composed of lamellar η phase about 1~20μm in length, granular γ′ phase in size of 30~80nm, and a small amount of carbonitride. The precipitated phases of heat affected zone are mainly composed of granular γ′ phase in size of 10~20nm and few of η phase on grain boundary. Dendritic structures are formed in fusion zone, Nb, Ti, and Al are extensively rejected into the interdendritic liquid and the eutectic constituents are form in size of 2~6μm. There are fine granular γ′ phase in size of 10nm in gamma dendrites. The micro hardness of base metal is lower than that of heat affected zone and fusion zone. Micro hardness of different zone is depend on the particle size of γ′ phase. Stress rupture process is composed of creep crack growth, rapidly crack growth and final fracture. Intergranular fracture is occurred in creep crack growth zone, mixed of intergranular and transgranular fracture is occurred in rapidly crack growth zone and transgranular fracture is occurred in final fracture zone. The creep crack imitated in the surface of HAZ of weld specimen. Because of low content of intergranular η phase and oxidation of grain boundary in crack tip, the stress rupture life and elongation are lower than those of GH4169D base metal.

Abstract:Aircraft ice accumulation has always been one of the important factors that threaten the safety of aircraft. However, the traditional aircraft de-icing method is unable to cope with the changes of all-electric aircraft and intelligent flight in the future. A new composite material based on Ni, CNT and LIT-PDMS is proposed in this paper, which can make use of eddy current thermal effect for non-contact de-icing, and maintain its reliability in the complex working environment of aircraft. The ni-cnt/lit-pdms composite has a static contact Angle of about 106.5°, which is hydrophobic and can effectively prevent water droplets from accumulating on the surface of the aircraft and thus freezing; When the input voltage of the induction heating device is 30V, the maximum equilibrium temperature of its heating is about 119℃, and it can be heated several times with good thermal stability, only need 232 s to completely melt 20g of ice; the internal conductive network of composites has good stability and resilience after theε=0.001 30 times tension. Ni-CNT/LIT-PDMS composites material can complete the aircraft de-icing work, to ensure flight safety.

Abstract:Amorphous alloys possess excellent mechanical properties, corrosion resistance, and magnetic properties, and are a new structural and functional material with significant application potential. However, the preparation of amorphous alloys via traditional methods is restricted by the critical cooling rate, and the forming size is also limited; these factors restrict the application of amorphous alloys. However, the preparation of amorphous alloys via spark plasma sintering (SPS) is not limited by the critical cooling rate, and SPS can therefore produce larger amorphous alloys. This paper summarizes the research progress of the preparation of amorphous alloys via SPS from the aspects of the densification mechanism, process parameters, comparative study of properties, and numerical simulation, and analyzes its difficulties and future development directions.

Abstract:The fifth group metal element V with the body-centered cubic (BCC) structure has higher permeability, better mechanical properties and lower price than Pd metal. Due to these merits, various vanadium alloy membranes have been developed to show greater resistance to embrittlement than pure V, which are a promising alternative for existing commercial Pd-Ag alloy membranes. In this paper, we present a review for the hydrogen permeation principle, ductile-to-brittle transition hydrogen concentration and the permeability of vanadium alloy membranes reported in the literature and give some perspectives about the future development.