High-strength aluminum alloy have become one of the most commonly used metal materials for aerospace and automotive application parts due to its high strength， low density， excellent ductility and corrosion resistance. Wire arc additive manufacturing （WAAM） has the ability to rapidly in-situ form and manufacture complex structural parts， and is very suitable for the manufacturing of medium or large high-strength aluminium alloy parts. The current status of high-strength aluminum alloy WAAM processes and equipment， the inherent properties and defects of high-strength aluminum alloy WAAM， and the main performance optimization methods were comprehensively analyzed in this paper. The inherent characteristics of the microstructure and properties as well as the impact of hybrid additive manufacturing technologies on the microstructure and properties were discussed. Opinions are put forward on issues such as metallurgical defects， characteristic performance requirements， the advantages and disadvantages of various optimization processes in WAAM. Development directions such as a comprehensive evaluation system， composition design and wire development， special heat treatment systems and synergy of composite additive manufacturing technology are proposed. Such proposals are expected to provide references for the performance improvement and application promotion of high-strength aluminum alloys manufactured via WAAM.

Laser additive manufacturing （LAM） enables the integrated direct formation of high-performance metallic components with complex geometry. However， the non-uniform distribution of temperature gradients， in-situ heat treatment effects， non-equilibrium solid phase transformations， and heterogeneous microstructure during the process result in intricate residual stresses that significantly affect the quality and overall performance. A comprehensive review of residual stress in LAM by introducing its fundamental definition and classification is provided in this paper. Furthermore， the particularity， formation mechanisms， characterization methods， and regulation techniques associated with residual stress in LAM is systematically reviewed. The subsequent sections introduce various characterization methods for residual stress in LAM components， along with their respective characteristics. Additionally， the applicability， advantages， and disadvantages of each method are presented. Furthermore， the methods for controlling residual stress can be categorized into post-treatment control and in-situ treatment control. Finally， the joint effect of different types of residual stress should be considered in the study of the cause and evolution mechanism of residual stress in LAM. The characterization method of residual stress should be integrated with various methods to facilitate mutual verification. To mitigate the impact of stress concentration on the printing process and resultant quality， as well as minimize the influence of post-processing stress on part accuracy， it is imperative to investigate in-situ control methods for residual stress and explore real-time online monitoring techniques for LAM.

Refractory high entropy alloys have excellent high temperature mechanical properties， but the high temperature oxidation resistance has always been one of the limiting factors in their application. Four kinds of refractory high entropy alloys AlNbTaTiZr， AlMoNbTiZr， AlMoNbTaTiZr and AlMo_0.5NbTa_0.5TiZr were designed and prepared by laser additive manufacturing technology. The oxidation mass gain of AlNbTiZr-based refractory high entropy alloys was measured at 900 ℃ and 1000 ℃， and the oxidation layer structure of different samples was studied. The effects of Mo and Ta on the high temperature oxidation resistance of AlNbTiZr-based refractory high entropy alloys were compared and analyzed. The results show that the four kinds of as-deposited high entropy alloys prepared by laser additive manufacturing are BCC＋HCP dual-phase structures. The dendrites are mainly BCC phases with high melting points， and a small amount of HCP phase rich in Al and Zr is distributed among the dendrites. AlNbTaTiZr shows the best oxidation resistance after oxidation at 900 ℃ and 1000 ℃ for a long time， and Ta instead of Mo to some extent improves the oxidation resistance of refractory high entropy alloys.

Wire-arc additive manufacturing is a new type of manufacture using wire as filling material and arc as a heat source， making it easier to manufacture complex-shaped and big-sized parts. The reciprocating and unidirectional process path experiment was conducted. The inclined wall made by unidirectional path has better morphology， less splash， and a smoother surface. The simulation model of AM11 reciprocating and unidirectional manufacturing path was established in finite element software and solved. The simulation results show that the unidirectional path deposition temperature is 267.4 ℃， the deposition thermal stress is 357.4 MPa， the reciprocating path deposition temperature is 307.0 ℃， and the deposition thermal stress is 420.4 MPa， the heat accumulation and thermal stress of unidirectional path are lower than that of reciprocating path. AM11， AM12， and AM21 inclined wall samples with different slope factors by wire-arc additive manufacturing in unidirectional path were prepared， and their microstructure and properties were analyzed. The results indicate that the grain size of AM11， AM12， and AM21 is 35， 39 μm， and 42 μm， there is more precipitated β-Mg₁₇Al₁₂ in AM21 thin-walled grains， which has larger and more dimples than that of the other two samples. The micro-hardness values of AM21 and AM11 are both about 81.5HV， higher than 73.1HV of AM12. The horizontal and vertical tensile strengths of the AM21 inclined wall sample are 255.7，224.4MPa， the yield strengths are 103.8，96.0 MPa， and the elongations reach 13.1% and 8.2%. The tensile strengths and elongations are both greater than those of AM11 and AM12 samples， but the yield strengths are close. The AM21 inclined wall has much better strength and plasticity， and verify that the more perpendicular the inclined wall of magnesium alloy arc additive manufacturing is， the better the mechanical properties such as strength and plasticity.

The stereolithography 3D printing technology provides a new technical solution for the preparation of complex structure SiC ceramic parts， but the characteristics of high light absorption and high refractive index of SiC lead to a common problem that printing is difficult to cure. SiO₂ with low absorbance and low refractive index was added to SiC ceramic matrix powder as filler to improve the curing property and printing accuracy of SiC ceramic paste. The effects of different amounts of SiO₂ on the rheology， stability and curing properties of the slurry and its mechanism were studied. The green body with high precision and good surface quality was prepared by stereolithography 3D printing technology， and the microstructure and properties of the green body were tested and analyzed. The results show that the adding SiO₂ to the SiC slurry can reduce the viscosity， improve the stability， and improve the curing property of the slurry. The addition of SiO₂ can significantly improve the surface roughness of the SiC green body and make the bending strength increase at first and decrease then.

To improve the quality of laser cladding， a finite element analysis process was established， focusing on laser power， scanning speed and powder feed rate as the main process parameters， aiming to reduce the research and development cycle and economic costs of optimizing cladding process parameters. By comparing the temperature and stress field simulation of GX4CrNi13-4 martensitic stainless steel laser cladding data with experimental results， the forming quality under different parameters is verified， optimizing the laser cladding process parameters. The results indicate that the adjustment range of laser power should be controlled between 1800 W to 2000 W to avoid substrate penetration and ensure sufficient density； increasing the powder feed rate effectively reduces temperature and residual stress. Among the three process parameters， laser power has the most significant impact on cladding quality. A comprehensive analysis of density and microhardness tests to assess the cladding quality and residual stress distribution under different parameters reveals that the optimal combination of process parameters is a laser power of 1800 W， scanning speed of 10 mm/s， powder feed rate of 10 g/min. The experimental results are consistent with the trends of stress field simulations， further validating the accuracy of the simulation data.

Ti-6Al-4V alloy is widely used in aerospace and chemical equipment manufacturing due to its good strength, plasticity, toughness, corrosion resistance and weldability, but its hardness and abrasion resistance are not high enough to limit its service life under frictional wear conditions to some extent. Ti-6Al-4V alloy homogeneous cermet cladding layer with TiC-added phase was additively prepared based on the optimized process method of laser cladding, and the strengthening effect of TiC enhancement with respect to the cladding layer microstructure as well as the basic mechanical properties was characterized and verified. The results show that the main phases of the cladding layer include α-Ti, β-Ti and TiC, of which TiC is supersaturated and precipitated within the cladding layer. Due to the difference in the supercooling degree at different locations of the cladding layer, the precipitated TiC is mainly in the form of fine particles at the top of the cladding layer, while it is mainly in the form of dendrites and petals in the middle of the cladding layer. The bottom of the cladding has a new wheat spikes precipitation shape, while no significant TiC precipitation is seen in the dilution zone. The average microhardness of the cladding layer is 530HV_0.5, which is 61% higher than that of the substrate; the average friction coefficient of the cladding layer is 0.3583 at 35 N load, which is 11% lower than that of the substrate, and the volume wear rate is about 87% that of the substrate, and the wear is in the form of adhesive wear and abrasive wear.

The TiC/IN625 coatings were prepared on 45 steel substrates by using extreme-high-speed laser cladding(EHLA) technology. The effect of different heat treatment temperatures(800, 1000 ℃ and 1200 ℃) on the microstructure, surface morphology, residual stress and corrosion resistance of TiC/IN625 coatings was analyzed. The results show that the coating segregation phenomenon is alleviated with the increase of heat treatment temperature. The distribution of Ti elements in the HT1000 coating is more uniform than that in the HT0 and HT800 coatings. The part Laves phase in the HT0 coatings starts to dissolve in the HT1000 coatings, releasing Nb elements that recombine with C and Ti elements to generate MC (M=Nb, Ti) carbides. The large-sized carbides in the microstructure of HT1200 coatings surface dissolve. The other elements, such as Ti and Ni, more homogeneously distribute and diffuse into the inter-dendritic region. The residual stress on the HT0 coatings surface is mostly expressed as residual tensile stress, with a maximum value of 362 MPa. The electrochemical corrosion tests indicate that the open-circuit potential is increased from －0.139 V for the HT0 coatings to －0.132 V for the HT1200 coatings. The charge transfer resistance (R_ct) of HT800, HT1000 and HT1200 coatings is also larger than that of the HT0 coatings, with an increase of 46.2%, 31.2% and 64.3% compared to the HT0 coating's 4.785×10⁵ Ω∙cm², respectively.

In order to expand the application of polypropylene (PP) in 3D printing technology and improve its mechanical properties, PP/polyethylene terephthalate (PET) blend filaments were prepared by extruding PP with PET using melt blending. The rheological behavior, crystallization structure, melting and crystallization behavior, microstructure, mechanical properties of the filament blends and 3D printed samples with different mixing ratios of PP, PET were analyzed. The results show that the viscosity of PP/PET blends decreases with the increase of shear rate and exhibits shear thinning behavior. PET acts as a nucleating agent and does not change the crystal shape of PP during PP crystallization. The melting temperature of PP is about 150 ℃, and the crystallization temperature increases with the increase of PET concentrations. The PP matrix and PET dispersed phase have obvious "sea-island" structure, in which PET is the "island" phase, with a diameter of 2-5 μm. With the increase of PET concentrations, the tensile strength of filament blends is improved. Simultaneously, the tensile strength and the impact strength of the 3D printed samples is improved. However, the mechanical properties of 3D printed samples are generally lower than those of filament blends due to interlayer interaction.

TCGH(TC4+GH4169)composite material was prepared by selective laser melting(SLM). The optimum forming process parameters of TCGH composite material were investigated, and the microstructure and mechanical properties of as-deposited samples and heat-treated samples were studied. The results show that the optimum process parameters for fabrication of TCGH composite material are scanning speed of 900 mm/s with laser power of 150 W, and density higher than 99.5%. The addition of GH4169 powder changes the solid phase transformation behavior of TC4 titanium alloy material, and the as-deposited structure shows obvious high temperature solidification characteristics, which makes the forming characteristics of progressive scanning overlap and layer-by-layer scanning accumulation obvious. The original coarse columnar β grain size along the printing direction is significantly reduced, and the tensile strength of the composite is improved. Compared with the as-deposited sample, the microstructure of the heat-treated sample is transformed into a near-equiaxed structure. At the same time, with the increase of heat treatment temperature, the dissolution of the second phase leads to the dominant solid solution strengthening effect of the composite material, which improves the tensile strength and plasticity of the composite material.

An experimental study on high cycle fatigue behavior of selective laser melting (SLM) TC4 alloy was carried out. The fatigue properties of the alloy under two sampling directions (horizontal and vertical) and two temperatures (room temperature and 400 ℃) were compared and analyzed. Also the feasibility of improving the fatigue properties of the alloy by hot isostatic pressing (HIP) was explored. The results show that the fatigue properties of the alloy after annealing are significantly anisotropic, and the fatigue properties of the vertical samples are higher than that of the horizontal ones. Compared with room temperature, the fatigue life of the alloy at 400 ℃ is reduced, but the anisotropy still exists. After hot isostatic pressing, the fatigue life of the alloy presents a certain degree of improvement, and the anisotropy of fatigue properties decreases. The fracture analysis shows that the cracks of SLM TC4 alloy mainly originate from surface and subsurface defects which are mainly pores. The statistical analysis shows that the source defect size of vertical samples is lower than that of horizontal samples, which is the main reason for the decrease of fatigue properties of horizontal samples. After hot isostatic pressing, cracks in both horizontal and vertical samples of the alloy are generated at the surface slip, and the porosity of the alloy is significantly reduced without obvious defects, and the decrease in the number of defects is the main reason for the improvement of fatigue properties of the alloy.

To analyze quantitatively various indexes of wire arc additive manufacturing components of 2319 aluminum alloy, the expressions of curved surface between different process parameters, porosity and tensile strength values were fitted, and the "process-structure-property" corresponding rule was established. In addition, a normalized fuzzy evaluation model was developed for process parameters, organizational defects, and mechanical properties using the generalized fuzzy synthesis operation rule. The purpose of this model was to obtain the optimal process parameters. The results show that the porosity generally increases with the wire feeding speed rising.Then the porosity generally decreases with a decrease in scanning speed. When the scanning speed is 0.035 m/s, the correlation between porosity and tensile strength is the lowest, with a correlation coefficient (coefficient of determination, COD) of only 0.6. The comprehensive evaluation score of the expert is the highest when the wire feeding speed is 5.0 m/min and the scanning speed is 0.025 m/s, indicating that this combination of process parameters is optimal.

Nickel-based superalloys have attracted significant attention due to their outstanding high-temperature strength, corrosion resistance, and oxidation resistance, and are widely used in aerospace and other fields. This article provides a comprehensive review of the preparation methods, common grades, and microstructure and properties of additive manufactured nickel-based superalloys, summarizes the current issues, and proposes future areas for exploration. Nickel-based superalloys prepared by metal additive manufacturing technology have excellent performance, can achieve precise forming of complex components, and have minimal material waste during the manufacturing process. They are expected to become an important production process for nickel-based superalloys components in fields such as aerospace. Common methods for additive manufacturing of nickel-based superalloys include laser powder bed melting, directed energy deposition, and arc additive manufacturing. Powder bed melting is widely used for manufacturing high-precision and complex parts, but it has a relatively slow manufacturing speed and higher equipment and material costs. Directed energy deposition has higher degrees of freedom and flexibility and can be used to prepare functional gradient materials, but it has lower accuracy. Arc additive manufacturing has lower equipment and material costs and is suitable for rapid manufacturing of large parts, but the surface roughness of the alloy produced by this method is poor and requires additional processing or post-treatment. Nickel-based superalloys widely studied in the additive manufacturing process include IN625, Hastelloy X, and other solid solution strengthened alloys, as well as IN718, CM247LC, IN738LC, and other precipitation strengthened superalloys. Compared with traditional casting and forging methods, the unique layer-by-layer forming and rapid cooling and heating process of additive manufacturing result in a coarse columnar grain structure and a unique microstructure with a large number of fine grains. It also forms unique melt pool structures and dislocation cell structures. However, the alloys obtained by additive manufacturing generally require heat treatment to control grain structure and precipitated phases, which affects the mechanical properties of the alloy. In addition, the mechanical properties of additive manufactured nickel-based superalloys are also related to specific preparation methods and alloy types. Although additive manufacturing has been widely used in the preparation of nickel-based superalloys, there are still issues such as anisotropy in microstructure and properties, high sensitivity to alloy cracking, and a lack of corresponding specifications and standards. In the future, further exploration is needed in areas such as heat treatment, customization and development of specialized alloys, investigation of the process-structure-function relationship, and computational modeling.

Wire arc additive manufacturing (WAAM) has received extensive attention from researchers due to its high deposition rate, high material utilization, low cost, and ability to manufacture large-scale components. It is expected to be widely used in rapid forming of magnesium alloys. The current types and requirements of wires used in WAAM of magnesium alloy were summarized. Then, the current preparation methods suitable for WAAM of magnesium alloy were introduced. The manufacturing technology, deposition mechanism, microstructure and mechanical property of various WAAM-processed magnesium alloys were discussed. Finally, the problems such as the few types of available wires and the uncontrollable shape and property of components for wire arc additive manufacturing of magnesium alloys were analyzed. The optimization of properties and application of components for wire arc additive manufacturing of magnesium alloys were forecasted.

TiB was planted into the matrix titanium alloy through the rapid solidification process, and the new ultrafine network reinforced titanium matrix composites (TMCs) powder was formed. Based on the laser additive manufacturing technology, a new titanium matrix composite with alternate distribution of equiaxed network and columnar network structure were creatively fabricated, the formation mechanism of the network structure was systematically discussed, and the mechanical properties of the super-solidified TMCs by additive manufacturing were tested. The results indicate that the network structure (about 9 μm) of the additively manufactured TiB/Ti composites is mainly composed of in-situ nano-TiB whiskers, presenting two crystal structures of B₂₇ and B_f. The direct introduction of B element is easy to form constitutional supercooling at the solidification interface. The equiaxed α phases are obtained by promoting the alternating formation of equiaxed/columnar network structure and refining the grain size. In addition, the formed nano-TiB network structure, not only inhibits the crack deflection and passivate cracks, but also confines the large number of slip lines inside the TiB network structure via in-situ observation, inducing high-density dislocations at the grain boundaries, which limites its plastic deformation, and greatly improves the strength of the composites. The additively manufactured TiB/Ti composites increases the tensile strength by 42%, and maintains the elongation of about 10%.

Laser repair technology has the advantages of short time, high efficiency, low cost and good mechanical properties, and has great development potential. Al-7.5Mg-0.3Sc-0.28Zr was used as the repair material to conduct laser repair experiments on 5083-H112 aluminum alloy used in rail transit, and a dense and defect-free repair sample was obtained. The microstructure and properties of the sample were studied, and the feasibility of laser repair of aluminum alloy was discussed. The results show that the transition zone near the fusion line can be divided into repair zone, partial melting zone, heat affected zone and base metal. The grains in the repaired area are completely equiaxed, consisting of a fine-grained band with an average grain size of 4.95 μm and a coarse-grained region of 18.34 μm respectively. In the transition area from the repair zone to the partial melting zone and then to the heat affected zone, the content of Al element gradually increases, the content of Mg element gradually decreases, and the hardness decreases gradually. The heat-affected zone and the base metal are not softened after the repair. Due to the rapid solidification of laser additive manufacturing technology, the fine-grain band near the fusion line has larger stress concentration, and the residual stress in the heat affected zone and partial melting zone is small due to the small heat input. The yield strength of the repaired sample of (152±2) MPa is 89.4% of the base metal, the tensile strength of (305±5) MPa is 100% of the base metal, and the elongation rate of (15.5±0.5)% is 85.2% of the base metal. Fracture occurs in the weaker base metal. Laser repair of aluminum alloys is feasible and has broad application prospects.

A three-dimensional finite element thermal model was established, combined with the finite element software ANSYS, and the simulation of applying a Gaussian heat source and the printing process of WC-12Co cemented carbide was achieved with the use of APDL commands and the birth-death unit method, and the temperature field distribution of WC-12Co cemented carbide in the laser powder bed fusion (LPBF) shaping process was finally obtained, and the effects of different process parameters (laser power, scanning speed) on its temperature field distribution and melt pool characteristics were investigated. The results show that the forming process of WC-12Co cemented carbide in LPBF process can be effectively simulated by using finite elements. In addition, the isotherms located at the front of the heat source are denser than those at the tail, with a larger temperature gradient; and the temperature in the center of the melt pool at the terminal edge of the scanning path is the highest. As the laser power increases and the scanning speed decreases, the width, depth and length of the molten pool increase accordingly. Relevant experiments were used to analyze the effect of different process parameters on grain size, and it is found that the grain size decreases with the increase of scanning speeds and increaseds with the increase of laser power; but too high laser power can cause certain thermal cracking phenomenon.

The influence of solid solution treatment on microstructure, tensile properties and residual stress of AlSi10Mg alloy prepared by selective laser melting was investigated by optical microscope, field emission scanning electron microscope, transmission electron microscope, tensile tests and Raman spectrometer. The results indicate that the as-built alloy has a fine microstructure and high strength, but there is obvious anisotropy and significant residual tensile stress. Both the ultimate tensile strength and the yield strength can be improved significantly by direct artificial aging treatment for as-built alloy. However, the morphologies of molten pools and eutectic silicon of aged alloy are as basically same as that of as-built alloy. The solid solution treatment can remarkably improve the anisotropy of microstructure and tensile property, and completely eliminate the residual tensile stress. Meanwhile, it also leads to structural coarsening, resulting in the ultimate tensile strength and yield strength are only about 50% of as-built alloy. For the solid solution treated alloy, there is no obvious change of microstructure, anisotropy and residual stress after artificial aging treatment. The ultimate tensile strength and yield strength reach 330 MPa and 270 MPa respectively, with the elongation after fracture about 10%-11%. The improvement of strength after artificial aging treatment is attributed to the precipitation of GP zone.

AlCoCrFeNi_2.1 eutectic high-entropy alloy is characterized by a fine, homogeneous, and regular lamellar structure, as well as good organizational structure and mechanical properties with both strength and plasticity over a wide range of temperature (70-1000 K) and compositional deviation, thus making it the most widely studied eutectic high-entropy alloy at present. In this paper, regarding the additive manufacturing of AlCoCrFeNi_2.1 eutectic high-entropy alloy, the influence of different processes and process parameters on the microstructure and mechanical properties of the alloy was reviewed, and the phase distribution, microstructure, and strengthening mechanism of AlCoCrFeNi_2.1 eutectic high-entropy alloy prepared by the selective laser melting technology were highlighted. Finally, it points out the differences and deficiencies in phase formation mechanism and organization evolution process of the current additive manufacturing AlCoCrFeNi_2.1 eutectic high-entropy alloy and puts forward the development direction of material modification of AlCoCrFeNi_2.1 eutectic high-entropy alloy as the substrate of the material modification and the new technology of additive manufacturing high-entropy alloy, which will provide ideas for the promotion of the industrialized application of the alloy.

The lightweight high entropy alloys have shown great application value in the lightweight structural materials. Laser melting and laser additive manufacturing technology provide new ideas for the development of high entropy alloys due to their extreme metallurgical conditions. Al_xNbTiV(x=0.5-7) and AlNbTi_yV(y=1-7) button samples were prepared by laser melting technology, and their phase structure, microstructure and hardness were systematically studied. The results show that the Al content has a significant effect on the phase structure and microstructure of the alloy. When the Al content is low (x ≤ 2), the Al_xNbTiV alloy is composed of BCC single-phase solid solution. When the Al content is high (2 ≤ x ≤ 7), intermetallic compounds appear in the alloy. With the increase of Al content, the BCC and TiAl phases change into TiAl₃ and NbAl₃ phases. Ti content in a certain range (y ≤ 7) will not affect the phase structure of the alloy. AlNbTi_yV alloys are composed of BCC single-phase solid solution. The content of Al and Ti has a great influence on the hardness of the alloy. When the Al_xNbTiV alloy is composed of BCC single phase, the hardness of the alloy increases with the increase of Al content, and the appearance of intermetallic compounds makes the hardness of the alloy no longer change with the change of Al content. The hardness of AlNbTi_yV alloy decreases with the increase of Ti content.

Metal lattice structural materials are widely used in aerospace, automotive industry, and other fields due to their advantages of lightweight, high specific strength, energy absorption, and porosity. High strength and toughness FeCrNi medium entropy alloy (MEA) was taken as the research object, and selective laser melting (SLM) was used to prepare FeCrNi medium entropy alloy lattice structure materials with four simulated lattice structures: BCC, BCCZ, FCC and FCC. The microstructure, mechanical properties, and deformation behavior of these materials were systematically studied.The results indicate that the FeCrNi medium entropy alloy lattice structure prepared by the skip scanning strategy has high node overlap quality, dense interlaced stacking of molten pools, and uniform and fine grains. When the relative density is similar, the specific strength and specific energy absorption values of BCC, FCC, BCCZ, and FCCZ lattice structures increase sequentially.The specific energy absorption of FeCrNi medium entropy alloy material with FCCZ lattice structure reaches 49.8J·g^-1, significantly higher than that of Ti6Al4V and 316L stainless steel lattice materials.The finite element simulation analysis shows that the presence of Z-shaped pillars increases the apparent strength and stiffness of the lattice material, and leads to a transition in deformation behavior from bending dominated to tensile dominated, which is the main reason for the strength improvement of the FCCZ lattice structure.

In order to study the effect of Al content on the microstructure properties of FeCoCrNi alloy, Al_xCoCrFeNi high-entropy alloy (0≤x≤0.9) was prepared by multi-channel laser cladding. The phase composition, microstructure, chemical composition and hardness of the alloy were test by X-ray diffractometry, metallography microscope, scanning electron microscope, electron probe and microhardness tester. The results show that with the increase of Al content, Al_xCoCrFeNi high-entropy alloy changes from single FCC phase (x≤0.35) to FCC+BCC biphase structure (0.35 < x < 0.85), and finally to BCC structure (x≥0.85). The microstructure of the high entropy alloy consists of epitaxial columnar dendrites and uniform equiaxed dendrites. When Al content reaches to x=0.5, characteristic structure of spinodal decomposition with alternating light and dark contrast starts to appear between the dendrites, which consists of disordered phase A2 and ordered phase B2.The microhardness test results show that the microhardness of Al_xCoCrFeNi alloys almost increases with the increasing Al content and a total of 146% improvement has been achieved when the Al content increases from x=0 to x=0.9. It should be noted that cracks begin to appear in the alloy when the Al content increases to a certain value (x≥0.6).The size and density of cracks increase with the increase of Al content.There are two main reasons. Firstly, the hot-cracking increases since the solidification range widen and their viscosity values near the solidification temperatures increase with the increasing Al content.Besides, cold cracking also increases as the brittle BCC and σ phases increase with the increasing Al content.

Molten pool monitoring is the basis of forming process optimization， playing a pivotal role in improving the formation quality. A machine vision monitoring system was set up for the laser cladding process. Based on the OpenCV software library， a method combining K-means image segmentation and dual threshold Otsu image segmentation was proposed， which realizes the accurate distinction between molten pool and plume with the accuracy of extracting geometric features of molten pool contour up to 95%. By designing an orthogonal experiment of laser cladding Ti-6Al-4V metal powder， typical cladding samples were selected to analyze the width and shape change of the weld pool in time domain， obtaining the fluctuation rule of the weld pool of the cladding layer. The results show that the fluctuation frequency and amplitude of the molten pool are affected by the process parameters and their combinations， and gradually stabilize with the progress of the cladding. Abnormal fluctuations in the molten pool during the cladding process are conducive to the positioning and identification of cladding defects， helping to optimize process routes.

Magnesium alloy as the most potential light structural material， has the advantages of high specific strength， specific stiffness and easy recycling， which contributes to the realization of lightweight in the industrial field. Compared with the traditional manufacturing technologies， the new and advanced manufacturing technology of additive manufacturing represent for high manufacturing efficiency， excellent performance， and forming complex structures. The technology of additive manufacturing for magnesium alloy， which has broad application prospects in the industrial field， is urgently required to be studied. In this paper， the recent studies of the three major additive manufacturing technologies for magnesium alloy：selective laser melting， wire+arc additive manufacturing， and friction stir additive manufacturing were summarized and analyzed from the aspects of forming characteristic， defect control， and features of microstructure and property.Finally，the developments in shape and performance control of the additive manufacturing technology for magnesium alloy：simulation analysis， process control， and heat source regulation were discussed.

The three-dimensional small crack growth behavior of selective laser melting (SLM) TC4 alloy was investigated by in-situ observation fatigue test method, and the long crack growth curve was measured by load reduction method under the same experimental conditions. The results show that at the early stage of small crack growth, the fatigue crack growth(FCG) rate fluctuates obviously under the influence of microstructure, and the FCG path is zigzag. With the increase of crack length, the influence of microstructure decreases, and the FCG path is straight, and the FCG rate increases steadily with the crack length. Internal defects can still reduce alloy fatigue life. Considering the small and long crack growth data, it is demonstrated that the small crack can still propagate under threshold value of long crack, and under the same stress intensity factor amplitude ΔK, small crack growth rate is higher than that of long crack. There is a typical "small crack effect", thus the small crack behavior should be considered when fatigue life prediction is carried out.

Stress corrosion cracking (SCC), as an important research direction in the interdisciplinary of material mechanics and corrosion electrochemistry, is one of the main failure modes of stainless steel components. Compared with traditional wrought technology, additive manufacturing (AM) 316L stainless steel has complicated microstructure and inherent defects including pores and lack of fusion places (LOF) caused by additive manufacturing process, resulting in more complex SCC behavior. Herein, the basic SCC behavior of 316L stainless steel was discussed in detail on the basis of the researches of AM316L stainless steel at home and abroad. The main contents include two stress corrosion mechanisms of hydrogen induced cracking and anodic dissolution. Two behavior of transgranular cracking and intergranular cracking were described. The effects of microstructure on SCC behavior of AM316L, including twins, different crystal interface, pores, LOF, and element segregation were summarized. The current situation and advantages of three in-situ characterization methods, including electrochemical noise, high-resolution neutron diffraction and three-dimensional morphology characterization were introduced, which are of great significance to explore the SCC behavior of AM316L. Finally, the prospective future of the research directions of SCC behavior of additive manufacturing stainless steel were proposed, including the research of SCC characteristics under high temperature irradiation environment and the principle of stress distribution and restructuration at crack tips.

Binder jetting is a promoted 3D printing technology with the advantages of low equipment cost, high manufacturing speed.Technical principle and procedure were firstly introduced, and the parameter, advantage and application of present commercial binder jetting system were summarized. The types of binder used in the printing process were listed. The interaction (sputtering, diffusion and permeation) between binder types and powder bed was analysed.In addition, the influence of printing parameters on the performance and accuracy of the printed part was also discussed, including powder properties (powder flowability, powder size distribution and mean size), printing parameters (layer thickness, binder saturation, print speed, droplet spacing and line spacing, drying time), post-treatment process (curing, burnout, sintering, infiltration). Binder jetting technology is an important development direction of additive manufacturing. There will be broad research and application prospects in the development of corresponding materials, binder design and post-treatment technology.

TC4-DT titanium alloy forgings with X-type groove were joined by laser additive joining technology. OM and SEM were used to characterize the macro and micro morphology of TC4-DT titanium alloy base metal, heat affected zone and joining zone. The microhardness of the three regions was measured by Vickers hardness tester. The tensile and impact tests of different samples were carried out at room temperature with universal testing machine and pendulum impactor. The results show that there is a dense metallurgical bond between the joining zone and the base metal. Distribution of microhardness from the base metal to the joining zone shows an increasing trend. The strength of TC4-DT alloy increases first and then decreases with the decrease of the proportion of the joining zone in tensile specimen, while the plasticity decreases. The impact toughness a_kU is above 55 J/cm². The position of U-shaped notch opening has a great effect on the impact toughness of the joining zone but not the bond zone.

The 6061 aluminium alloy is a heat treatable reinforced aluminium alloy containing magnesium and silicon as its main alloying elements. It is commonly used in the aerospace and automotive industries due to its excellent mass to strength ratio and high thermal conductivity, but is particularly susceptible to the formation of coarse columnar crystals and thermal tearing, particularly during SLM processing.TiH₂/AA6061 aluminium-based composite powders were prepared by the low-energy ball milling assembly modification method, and the titanium-containing 6061 aluminum alloy specimens were prepared by selective laser melting technique.The microstructure and mechanical properties of the samples with different TiH₂ contents were systematically investigates. The results show that the addition of 1% TiH₂ (mass fraction, the same below) results in the formation of a continuous equiaxed crystal zone at the alloy melt pool boundary, the average grain size decreases from 59.8 μm to 2.53 μm, and the coarse columnar grains and cracks inhibit, and with the addition of 1.5% TiH₂, the coarse columnar grains of the SLM specimens inhibit completely and only a few small columnar grains exist. The microstructure transformation is attributed to the enhancement of the constituent undercooling by Ti elements and the in-situ reaction to form L1₂-Al₃Ti nucleation particles, which form a coherent interface with the Al matrix and have a strong heterogeneous nucleation effect, thus significantly promoting the transformation from columnar to equiaxed crystals and grain refinement of the Al matrix. After selective laser melting, the tensile strength of 6061 aluminum alloy with 1% TiH₂ addition is 274 MPa, the yield strength is 238 MPa, and the elongation after break is 18%.

Aluminum alloy is an important light metal structural material, which has been widely used in aerospace and transportation industries. Wrought aluminum alloys generally require extrusion, rolling or forging after casting to be processed into finished products. However, this conventional casting-deforming-cutting subtractive manufacturing route has become increasingly difficult to meet the manufacturing demands of high efficiency and environmental sustainability. As an emerging manufacturing method, additive manufacturing (AM) provides brand-new possibilities for the manufacturing of aluminum alloys by depositing subsequent layers based on digital drawing files to make three-dimensional objects. However, most aluminum alloys are suffering from the various defect issues due to the manufacturing characteristics of laser-based AM processes and several intrinsic properties of aluminum alloys, which impair their mechanical properties and limit their industrial applications. Various defects and corresponding causes in additively manufactured medium- and high-strength aluminum alloys were reviewed in this paper. In addition, latest researches on eliminating defects and thus improving mechanical properties of AM aluminum alloys were summarized from three aspects: process parameter optimization, alloy composition optimization and nucleant agent addition. This work demonstrates that processing parameter and alloy composition should be regulated synergistically to improve the microstructures and mechanical properties of additively manufactured medium- and high-strength aluminum alloy, and the optimal heat treatment should also be inve-stigated.

High-entropy alloy coatings show great potential for improving the wear resistance of the stainless steel substrate. To investigate the effects of Cu/Si doping on the microstructure and high temperature tribological properties of FeCoCrNi high-entropy alloy coating, FeCoCrNiCu_x and FeCoCrNiSi_x series of high-entropy alloy coatings were prepared on the 304 stainless steel by laser cladding.The microstructure and phase distribution of the coatings were characterized by XRD, SEM and EDS, and the high temperature tribological properties of the coatings were tested by a high temperature friction and wear tester. The results show that both FeCoCrNiCu_x and FeCoCrNiSi_x high entropy alloy coatings form a single FCC-type solid solution with good metallurgical bonding to the substrate under suitable laser cladding parameters.The addition of Cu reduces the surface hardness of FeCoCrNi coatings, but improves the metallurgical bonding due to the increase of thermal conductivity of the coating; the addition of Si promotes grain refinement and improves the surface hardness of the coating. At 600 ℃, the addition of Cu/Si elements significantly improves the tribological properties of the coating, with the coefficients of friction of 0.24 and 0.19 for FeCoCrNiCu and FeCoCrNiSi coatings, respectively, and the wear rates are 1.58×10^-4 mm³·N^-1·m^-1 and 6.77×10^-5 mm³·N^-1·m^-1, respectively, which are 56.1% and 81.9% lower than FeCoCrNi coating.The main wear mechanisms of FeCoCrNiCu coating are oxidation wear, fatigue wear and slightly abrasive wear, while FeCoCrNiSi coating is oxidation wear.

To improve the surface hardness and wear resistance of Al-Pb alloys, pure aluminum (Al) surfaces coated with lead (Pb) layers were irradiated by using high current pulsed electron beam (HCPEB) to prepare Al-Pb alloyed layers with excellent properties. The surface roughness of the alloying layer was observed by 3D laser scanning microscope (LSM). Meanwhile, the micro morphology, structure and element distribution of Al-Pb coating before and after irradiation alloying were analyzed by field emission scanning electron microscopy (SEM) with energy dispersive spectrometer (EDS). In addition, the phase composition of the alloy layer was observed by X-ray diffraction (XRD). Moreover, the surface microstructure after alloying was characterized by transmission electron microscopy (TEM). Finally, the microhardness, average friction coefficient and wear rate of the sample surface before and after irradiation were tested, and the hardness and wear enhancement mechanism were analyzed. The strengthening mechanism of the surface performance was also summarized. The internal relationship between surface microstructure and surface properties of irradiated coatings was established. The results show that after HCPEB irradiation treatment, the Al substrate and Pb coating show good metallurgical bonding, and after 30 times of irradiation, the Pb-Al alloying layer with a thickness of about 10.2 μm is prepared. Compared with pure aluminum and the original coating, the diffraction peak of (111)_Al crystal plane is widened after 30 times of irradiation, and the position of the diffraction peak is also slightly shifted to the low angle direction, which means that the Al grains on the surface of the matrix are significantly refined after the surface alloying treatment of HCPEB, and the crystal cells expand, and the lattice constant increases. HCPEB induces the formation of sub crystals, dislocations, dislocation cells, a small amount of Al(Pb) solid solution and a large number of nanoscale Pb rich particles on the sample surface. The test results show that the hardness and wear resistance of Al-Pb coating surface are significantly improved after electron beam irradiation.

The additive friction stir deposition (AFSD) technology is a new solid-state additive manufacturing technology. The metal bars, powders, and wires are used as feedstock. During the additive process, the friction heat generated by the friction between feedstock and the plate and the plastic deformation heat generated by the severe deformation of feedstock form a viscoplastic deposition layer. The deposition layer is stacked layer by layer to form three-dimensional parts. Because of its solid phase characteristics, it has many advantages over fused-based metal additive technologies and has become a research hotspot in the field of additive manufacturing. In this paper, the latest research progress of AFSD technology at home and abroad was reviewed from four aspects of equipment development, microstructure evolution, material flow characteristics and mechanical properties change. The feasibility of the application of this technology in engineering practice was analyzed and the application prospect in the field of metal coating reinforcement for material repair parts of additive manufacturing was forecasted. Finally, it was pointed out that the heat generation mechanism, material flow characteristics, auxiliary optimization process, and intelligent equipment development are the future research directions.

Based on selective laser melting (SLM), the high speed steel samples with nearly full density and low defects were prepared by using the printing strategy consisted of preheated printing substrate, low laser power and slow scanning speed. The effect of solid-solution oil-quenching as well as 1-4 times high temperature tempering on the microstructure and mechanical properties of selective laser melted high speed steel was contrasted and analyzed. The results demonstrate that fine austenite grains can be obtained due to the high melting/cooling rate in SLM process, solving the problems of coarse ledeburite organization and carbide network in high speed steel. The structure of steel is martensite and retained austenite after solid-solution oil-quenching. High speed steel sample transformed into tempered martensite during multiple tempering, accompanied with a large number of micro-sized and nano-sized carbides precipitated. The quenched and triple tempered Tempered-Ⅲ sample has a hardness of 60HRC, a flexural strength of 3621 MPa and a bending fracture strain of 10.1%, exhibiting an outstanding combination of hardness, strength and toughness. The bending fracture strain of high speed steel decreases owing to the coarsening of carbides in four times tempering. The integration of SLM, solid-solution oil-quenching and high-temperature tempering, which forms the combined effects of fine-grain strengthening, martensitic hardening and precipitation strengthening, provides a new approach for complex shaped high speed steel parts with high strength and toughness.

The nano-SiC/AlSi7Mg mixed powder was prepared by mechanical mixing method. The specimens of nano-SiC particle reinforced AlSi7Mg composite were fabricated by selective laser melting (SLM). The relative density, phase and microstructure were observed and analyzed, and the microhardness and tensile properties were tested. The results show that the relative densities of SLM nano-SiC/AlSi7Mg composite are increased firstly and then decreased with the increase of scanning speed and scanning space, and the maximum relative density reaches 99.75%. The microstructure of specimens is similar to that of SLM-formed Al-Si alloys, and the network-structured Si phase is uniformly embedded in the α-Al matrix. There are nano-SiC agglomerates and Mg₂Si phase in the α-Al matrix, which has a similar distribution to Si. Compared with AlSi7Mg, the microstructure of specimens is changed from columnar to equiaxed grain, and the grains are significantly refined (the average grain size is 1.36 μm). Due to the addition of SiC, grain refinement strengthening and solid solution strengthening are produced, and the hardness and strength of composite are significantly improved. The hardness, tensile strength and yield strength reach 137.3HV, 448.3 MPa and 334.7 MPa, respectively. However, the elongation is reduced to 3.9%, and the fracture mode is mainly brittle fracture.

Infection after surgery is one of the common and most challenging clinical problems, and the development of new antibacterial coating is an effective strategy to solve this problem, which has important scientific and social significance. A bioactive coating with antibacterial function was prepared on the surface of a 3D printed porous titanium bone scaffold. It is discovered that silver (Ag) exists in the coating as a simple substance. As the Ag content increases (0%, 0.5%, 1%, 1.5%, mole fraction), the specific surface area of the mesoporous coating is decreased from 377.6 m²/g to 363.35 m²/g. In vitro mineralization results show that with the increase of Ag content, the apatite inducing ability is decreased slightly. At the same time, the antibacterial test demonstrates that the addition of silver markedly enhances the antibacterial performance of the scaffolds. Adding a small amount of silver (0.5%) can achieve 100% antibacterial rate. The MC3T3-E1 cells are cultured with the scaffolds for 1, 3 and 7 days, and it is found that the Ag-doped MBG coatings have good cyto-compatibility, and the addition of a small amount of silver can promote the proliferation of MC3T3-E1 cells. A simple dipping and pulling method was used to apply the Ag-doped MBG coating to the complex 3D printed titanium scaffolds with complex topological structure. The mineralization performance, bactericidal performance and cellular compatibility of the scaffold are significantly improved, providing a new idea for the further development of multifunctional bone implant scaffold.

High-strength aluminum alloys (2××× and 7×××, etc.) are widely used in aerospace, automobile and other fields because of their high specific strength and good machinability. With the development of high thrust-weight ratio engine and automobile lightweight technology, the demand for lightweight structural materials is increasing. Meanwhile, parts also present the "thin-walled, hollow and composite" tendency gradually, and the traditional processing methods of high-strength aluminum alloy are increasingly difficult to meet the requirements. As a common metal additive manufacturing (AM) technology, selective laser melting (SLM) is a great potential manufacturing technology for complex parts. SLM is expected to become an emerging technology to expand the application of high-strength aluminum alloys. However, due to their poor casting and welding properties, high-strength aluminum alloys easily produce the periodic hot cracks and coarse columnar grains during SLM, leading to unsatisfactory mechanical properties. Grain refinement is the key to overcome the inherent hot-tearing crack of SLMed high-strength aluminum alloys. The research progress in microstructure and mechanical property control of SLMed high-strength aluminum alloys in recent years was reviewed. The mechanical properties of alloys with different compositions were summarized. Importantly, the main strategies to suppress hot-crack formation in SLMed high-strength aluminum alloys were highlighted, including optimization of SLM process parameters and grain refinement by microalloying or addition of nanoparticles. It was pointed out that the main issue of SLMed high-strength aluminum alloys was the change of alloy composition on the comprehensive properties and heat treatment process was still unclear. The development trends were forecasted, such as designing new high-strength aluminum alloys and evaluating their comprehensive performances, using post-treatment process and other means to further improve the comprehensive performances of the alloys, and designing special grain refiners for SLM and investigating refinement mechanism.

Melt growth ceramics (MGC) is a new type of ceramic material with microstructure obtained by melting and solidification of raw materials. The clean and high-strength bonding interface shared by atoms makes it have excellent high-temperature mechanical properties and microstructure stability close to the melting point. It shows great application potential in the field of high thrust weight ratio aero-engine and heavy gas turbine hot end components in the future. Laser directed energy deposition (LDED) technology can effectively overcome the limitations of traditional preparation methods of MGC in terms of cycle, energy consumption and structural complexity. It provides a new solution for direct additive manufacturing of MGC components, and has become a research hotspot at home and abroad. Based on the introduction of the process principle of LDED technology, the microstructure characteristics and properties of different MGCs prepared by this technology at home and abroad were summarized in this paper, and the main research on the control of microstructure and cracking behaviour was comprehensively discussed. Based on the existing research progress, the development trend and key scientific problems to be further solved in this field were discussed. It was pointed out that inhibiting cracking and improving microstructure and properties are the primary problems faced at present. The development of materials and new processes is the key to breaking through the existing bottleneck and promote the development and application of MGC-LDED.

Ceramic casting mould is a kind of complex part which is used in the field of investment precision casting to mold the inner and outer structure of casting. With the increase of the complexity of casting, more delicate and complex casting mould is needed to meet the casting demand. However, the traditional ceramic casting method like injection molding has many disadvantages such as high cost, long research and development cycle, and it is difficult to meet the requirements of increasingly complex fine structure molding. As a rapid prototyping method, 3D printing technology can accurately form complex structures. Its application in casting production can not only solve the problem of forming complex structures, but also reduce the production cost and shorten the production cycle. The 3D printing technology in the application of the ceramic mould production was mainly expounded in this article. The research and application of the ceramic mould was introduced from the types and the features of 3D printing ceramic mould material, typical 3D printing mould technology and post-processing method of 3D printing mould technology. The future development of this technology was prospected, it was pointed out that 3D printing technology can effectively solve the molding problem of complex ceramic casting, so as to meet the casting demand of complex hollow structure metal parts.

In recent years, photocured ceramics has become one of the rapidly developing additive manufacturing technologies. Bioceramics have a promising future in tissue engineering due to their good cellular compatibility, however, a single bioceramic material is difficult to take into account both mechanical properties and biocompatibility, so the application and promotion are greatly limited. In this paper, the modification and design methods of bioceramic materials suitable for photocuring were reviewed. The comprehensive effects of material modification, surface modification, structural design and microstructural regulation on the biological properties such as bone conduction, bone induction, antibacterial, angiogenesis promotion and other biological properties as well as and basic mechanical properties of were discussed. It was pointed out that the function of photocurable bioceramics can be fully realized and its further application can be promoted through the combination of modification and regulation methods, and the realization and interaction mechanism of multifunction should be explored.