ISSN 0412-1961
CN 21-1139/TG
Started in 1956

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Grain Refinement of As-Cast Mg-RE Alloys: Research Progress and Future Prospect
Magnesium rare-earth (Mg-RE) alloy castings with a large size and complex structure exhibit versatile prospects in critical aircraft, aerospace, and defense fields owing to their ultralow density, excellent specific strength, and high-temperature resistance. The grain refinement of cast Mg-RE alloys. . .
Acta Metall Sin, 2022 Vol. 58 (4): 385-399    DOI: 10.11900/0412.1961.2021.00519
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Precipitation Behavior of Intermetallic Compounds at the Interface of Thick Plate Friction Stir Welded Al Alloy/Mg Alloy Joints Under Local Strong Cooling PDF (2940KB)
The evolution of microstrucutre during static recrystallization in FGH96 superalloy PDF (2913KB)
Research Progress on Surface Impact Strengthening Mechanisms and Application of Nickel-Based Superalloy PDF (2177KB)

Corrosion Behavior of Zn-2.0Al-1.5Mg Coatings to a Simulated Marine Atmosphere

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Effect of Flash Heating on Microstructure and Mechanical Properties of 2000 MPa Hot Stamping Steel PDF (2900KB)
Current Issue More>>
      11 May 2023, Volume 59 Issue 5 Previous Issue   
    Effect of Cold-Rolling Deformation on Microstructure, Properties, and Precipitation Behavior of High-Performance Cu-Ni-Si Alloys
    WANG Changsheng, FU Huadong, ZHANG Hongtao, XIE Jianxin
    Acta Metall Sin. 2023, 59 (5): 585-598.   DOI: 10.11900/0412.1961.2021.00208
    Abstract   HTML   PDF (4527KB)

    The advancement of integrated circuit manufacturing process and chip packaging technology has improved the performance requirements for lead frame copper alloy. In the field of high-performance copper alloys, balancing and improving mechanical and electrical conductivity (EC) has been a challenge. This work investigates the effect of different cold-rolling deformations (0, 65%, 75%, 85%, and 95%) on the microstructure, properties, and precipitation behavior of Cu-3.0Ni-0.60Si-0.16Zn-0.15Cr-0.03P alloy to enhance its comprehensive performance through process control. The deformation-aging process parameters of high-performance Cu-Ni-Si alloys were determined by comparing the precipitation and recrystallization initial temperatures, microstructures, and properties of the samples after aging. The effect of cold-rolling deformation on precipitation kinetics and mechanism was studied. By optimizing the process parameters, the properties of the alloy are observed to be better than the existing Cu-Ni-Si alloys after 95% cold-rolling deformation and aging at 450oC for 60 min, with an ultimate tensile strength of (841 ± 10) MPa, and an EC of (52.2 ± 0.3)%IACS. This work's relevant research findings can provide theoretical reference and data support for realizing the comprehensive property enhancement of high-performance copper alloys.

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    Segregation and Solidification Mechanism in Spray-Formed M3 High-Speed Steel
    LIU Jihao, ZHOU Jian, WU Huibin, MA Dangshen, XU Huixia, MA Zhijun
    Acta Metall Sin. 2023, 59 (5): 599-610.   DOI: 10.11900/0412.1961.2021.00282
    Abstract   HTML   PDF (6787KB)

    Spray forming of various steels and iron-based alloys has been investigated since the 1960s. The microstructure and properties of spray-formed steels are superior to those of cast material, typically resembling those of equivalent powder metallurgy steels. While the wight of the deposits produced in pilot-scale plants is typically less than 100 kg, in some cases, industrial plants are capable of producing preforms that weigh up to several tons. However, in actual industrial production processes, segregation can easily appear in the product structure, especially in large-scale high-speed steel. In this work, M3 high-speed steels with a 250 mm diameter after forging were prepared through spray forming to study their cross-section segregation morphology. An arc-spark direct reading spectrometer, an original position analyzer for metals, OM, SEM, and EDS were used to analyze the distribution of alloy elements and microstructure characteristics of the different parts of a cross-section area. The results show two segregation morphologies in the cross-section of spray-formed M3 high-speed steel: ingot segregation and ring segregation. Carbon and alloy elements are enriched in the ingot segregation, whereas carbon and molybdenum are mainly enriched in the ring segregation, where the degree of segregation is less than that of the ingot segregation. From edge to center, the morphology of carbide changes from plate to massive. In the ring segregation area, there were two morphologies of carbide: one is M6C-wrapped MC composite carbide of the network distribution and the other M6C and MC both nucleating at the carbide/matrix interface of the composite carbide. In the ingot segregation area, carbides were mainly distributed independently of massive M6C and MC, with severe carbide segregation in the macrostructure. On the basis of the above experimental results, the solidification and microstructural evolution of spray forming were discussed, and the slow cooling rate in the deposition stage was the fundamental reason for the above experimental results. It is believed that spray forming loses rapid solidification characteristics in the deposition stage when preparing large-scale products.

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    Critical Inclusion Size and Void Growth in Dual-Phase Ferrite-Bainite Steel During Ductile Fracture
    ZHAO Yafeng, LIU Sujie, CHEN Yun, MA Hui, MA Guangcai, GUO Yi
    Acta Metall Sin. 2023, 59 (5): 611-622.   DOI: 10.11900/0412.1961.2022.00293
    Abstract   HTML   PDF (3069KB)

    Ferrite-bainite dual-phase steel is widely used in the automotive industry owing to its high strength and excellent ductility. The impact of inclusions and void growth behavior in dual-phase steel is a major concern among researchers seeking to achieve better mechanical properties. To investigate this, a cross-length-scale multimodal method was employed to study the influence of local microstructures on void growth during ductile fracture of a dual-phase ferrite-bainite steel. During tensile testing, laboratory X-ray computed tomography (XCT) was used to measure the evolution of void volume. 3D-electron back scatter diffraction (3D-EBSD) provided information about the voids nucleated at both inclusion particles and bainite phases or their boundaries. Carefully controlled, broad-focused ion beam excavation was performed to reveal a new interface at a specific depth of the voids. Results showed that voids resulting from large inclusions are significantly bigger than either small inclusions or the bainite phase. Large inclusions lead to large voids even when the strain correlated with the growth of those voids is lower. An investigation of the dislocation densities surrounding the voids suggested that they may be related to the strain gradient around the different inclusion sizes. A critical inclusion size estimated to be around 1.85-2.86 μm was found below which nucleation occurs but with limited growth. The elevated rate of local dislocation multiplication due to local deformation gradient effects can impede the growth of smaller voids. The growth of voids is heterogeneous, and their shape correlates well with the deformability of the surrounding grains, as indicated by a Schmid factor weighted using the grain size. This weighted Schmid factor explains not only the shape of the voids but also sheds light on the ease of void coalescence based on the microstructures separating the voids.

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    Influence of Size Design on Microstructure and Properties of 304L Stainless Steel by Selective Laser Melting
    HOU Juan, DAI Binbin, MIN Shiling, LIU Hui, JIANG Menglei, YANG Fan
    Acta Metall Sin. 2023, 59 (5): 623-635.   DOI: 10.11900/0412.1961.2021.00248
    Abstract   HTML   PDF (4867KB)

    As one of the most promising metal additive manufacturing methods, selective laser melting (SLM) is very attractive for fabricating complex-shaped structure components of austenitic stainless steels in the nuclear field. SLMed austenitic 304L stainless steel has been demonstrated to have excellent mechanical properties and superior corrosion resistance due to the unique hierarchical microstructure produced by the ultrafast cooling rate and high-thermal gradient. Scanning tracks (T) and depositing layers (L) are key factors for geometry design by affecting the processing efficiency and the solidification structure of the components. Hence, it is essential to clarify the effecting mechanism of sample size and geometry on material performance. In this work, samples of different sizes are designed to study the influence of geometry on the microstructure and mechanical properties of 304L stainless steel components made via SLM. Various solidification conditions are achieved by varying the temperature gradients and cooling rates by adjusting T and L. Metallographic microscopic observations in samples with various T × L combinations demonstrate that a columnar structure is formed along the build direction, which is significantly impacted by the geometry effect. The columnar grains grow preferentially along the heat dissipation direction with an increase in the sample size. The columnar grains gradually change from having a low length-diameter ratio (LDR) with a rice grain shape to a higher LDR with a short rod-like shape and then a long strip shape. Grain coarsening could also be identified along with the formation of “long strip” columnar grains. Moreover, consistent microstructure evolution behavior is observed in large-sized samples. The influence of geometry on the mechanical properties is examined via tensile testing to demonstrate the decrease in yield strength and increased plastic elongation with the rise in sample size. As the sample size increases, the mechanical properties become consistent. The comprehensive analysis concludes that grain size and columnar grains play critical roles in determining the mechanical properties according to the Hall-Petch relationship. In larger-sized samples, “long strip” columnar grains with a high proportion could lead to a decrease in material strength and an increase in plasticity. The geometry mechanism affecting the solidification process, microstructure formation, and mechanical properties of 304L stainless steel processed by SLM is explored by combining the solidification rate and thermal gradient simulation results using ANSYS ADDITIVE.

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    Microstructure and Strength-Toughness of a Cu-Contained Maraging Stainless Steel
    WANG Bin, NIU Mengchao, WANG Wei, JIANG Tao, LUAN Junhua, YANG Ke
    Acta Metall Sin. 2023, 59 (5): 636-646.   DOI: 10.11900/0412.1961.2021.00599
    Abstract   HTML   PDF (5128KB)

    An increase in strength often leads to a decrease in the ductility and toughness of maraging stainless steels; this phenomenon is known as the strength-ductility/toughness trade-off dilemma in structural materials. Some studies have found that the introduction of submicro/nanometer-sized retained or reverted austenite could mitigate the strength-ductility/toughness trade-off of high-strength maraging stainless steels. In this work, a novel strategy to accelerate austenite reversion by Cu addition in a Fe-Ni-Mo-Co-Cr maraging stainless steel was studied. In addition, the aging behavior and its effects on the mechanical properties of a Cu-containing Fe-Cr-Co-Ni-Mo maraging stainless steel were systematically studied. Transmission electron microscope characterizations showed that Cu- and Mo-rich phases precipitated from the steel matrix in sequence during the aging process; more specifically, a part of Mo-rich phase nucleated at the Cu-rich phase and then grew. Moreover, along with the segregation of Cu and Ni, reverted austenite was formed gradually. With an increase in the aging time, the stability of the reverted austenite increased, resulting in a substantial increase in its toughness. After aging for 90 h, the yield and tensile strengths of the steel reached 1270 and 1495 MPa, respectively, and the impact energy and fracture toughness were 81 J and 102 MPa·m1/2, respectively, showing an excellent match of strength and toughness compared with commercial maraging stainless steels.

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    Effect of Heat Treatment on Mechanical Properties of Porous Ti55531 Alloy Prepared by Selective Laser Melting
    ZHANG Dongyang, ZHANG Jun, LI Shujun, REN Dechun, MA Yingjie, YANG Rui
    Acta Metall Sin. 2023, 59 (5): 647-656.   DOI: 10.11900/0412.1961.2021.00313
    Abstract   HTML   PDF (3846KB)

    Lightweight metallic cellular components with high strength have received extensive interest because they are desirable for structural components. Previously, titanium alloy cellular structures were formed using additive manufacturing with the selective laser melting or electron beam melting technique. Numerous techniques have been developed to improve their strength. Most of these studies have focused on structure topology design. The relationship between the strength and mechanical properties of their strut parent materials has gained considerable attention. XRD, OM, SEM, and compression tests were used to investigate the effects of heat treatment on the microstructure and mechanical properties of Ti-5Al-5Mo-5V-3Cr-1Zr (Ti55531) alloy porous materials prepared through selective laser melting. The results show that the microstructure in struts consist of α and β phases after solution treatment at a temperature between 750oC and 900oC followed by an aging treatment at a temperature between 500oC and 600oC. The volume fraction of the primary α phase in the struts decreases as the solution temperature rises, whereas the volume fraction of the secondary α phase increases. The strut parent material's compressive strength increases but its elongation decreases, resulting in a decrease in toughness. With the increase of aging temperature, the shape, size, and volume fraction of the primary α phase in the strut do not change considerably, whereas the volume fraction of the secondary α phase decreases and the size increases. The strut parent material's compressive strength decreases while elongation increases, increa-sing toughness. The compressive strength of the examined porous alloy is strongly connected to the toughness of the parent material of the struts, which can be effectively improved by adjusting the strength and plasticity of the struts through heat treatment. The above results will guide the design of lightweight metallic cellular components with high strength.

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    Effect of Post-Aging on Microstructure and Mechanical Properties of an Ultrafine-Grained 6061 Aluminum Alloy
    LIU Manping, XUE Zhoulei, PENG Zhen, CHEN Yulin, DING Lipeng, JIA Zhihong
    Acta Metall Sin. 2023, 59 (5): 657-667.   DOI: 10.11900/0412.1961.2021.00237
    Abstract   HTML   PDF (3315KB)

    Al-Mg-Si alloys are widely used in automotive body panels and parts of the engine owing to their low density, medium strength, high specific strength, good corrosion resistance and other characteristics. Currently, there are many studies on the precipitation behavior of undeformed Al-Mg-Si aluminum alloy, but there is a lack of research on the precipitation evolution and precipitation strengthening mechanism of ultra-fine grained 6061 aluminum alloy at different post-aging temperatures. In this study, the microstructure and mechanical properties of an ultrafine grain 6061 aluminum alloy produced by combining the equal channel angular pressing (ECAP) and post aging methods was comparatively evaluated via TEM, XRD, microhardness tests, and tensile tests. The results indicated that the average grain size of the alloy after two ECAP passes was refined to 210 nm. The average grain size of the alloy after the ECAP pass at 80oC and 20 min post aging was 278 nm; moreover, the fine needle β'', L phase, and Q' phase precipitates at nanoscale were dispersed in the matrix. Furthermore, the tensile and yield strengths were 514 and 483 MPa, respectively, while maintaining a remarkably uniform elongation of 15.1%. These results indicate that numerous dislocations introduced by ECAP in the matrix provide a location for the nucleation of the precipitate, which accelerates the precipitation kinetics during the post aging process. The high strength and toughness of the ECAP alloy after low temperature post aging can be attributed to the grain refinement strengthening, dislocation strengthening, and nanoprecipitation strengthening. Thus, the evolution of the aging precipitates during the ECAP and post aging alloy was analyzed.

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    Effect of Shot Peening of Substrate Surface on Cyclic Oxidation Behavior of Sputtered Nanocrystalline Coating
    HUANG Ding, QIAO Yanxin, YANG Lanlan, WANG Jinlong, CHEN Minghui, ZHU Shenglong, WANG Fuhui
    Acta Metall Sin. 2023, 59 (5): 668-678.   DOI: 10.11900/0412.1961.2022.00183
    Abstract   HTML   PDF (3093KB)

    In addition to changing the surface roughness of the superalloy, the substrate surface treatment can also modify the microstructure of the surface, which affects the high-temperature oxidation behavior of the high-temperature protective coating. However, there are few reports about the effect of superalloy surface treatment on the oxidation behavior of nanocrystalline coatings. In this work, nanocrystalline coatings were sputtered on the nickel-based single crystal superalloy after two different surface treatments of polishing and shot peening, and their cyclic oxidation behavior at 1100oC was investigated. The phase composition and microstructure of nanocrystalline coatings were characterized by SEM, XRD, and EDS. The results indicated that the cyclic oxidation kinetics of both nanocrystalline coatings at 1100oC were similar. A dense oxide film could be formed on the surface of nanocrystalline coatings, showing excellent oxidation resistance. However, the microstructure evolution of the interface between the nanocrystalline coating and shot-peened superalloy substrate differed from that between the nanocrystalline coating and polished superalloy substrate. The sustained formation of the γ′ phase in the nanocrystalline coating near the polished substrate/coating interface was observed during high-temperature oxidation. This phenomenon was not found at the nanocrystalline coating near the shot peened substrate/coating interface, while the continuous growth of the γ' phase was observed at the substrate.

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    Direct Alloying of Immiscible Tungsten and Copper Based on Nano Active Structure and Its Thermodynamic Mechanism
    WANG Hanyu, LI Cai, ZHAO Can, ZENG Tao, WANG Zumin, HUANG Yuan
    Acta Metall Sin. 2023, 59 (5): 679-692.   DOI: 10.11900/0412.1961.2022.00003
    Abstract   HTML   PDF (2933KB)

    W is usually used as plasma-facing components in nuclear fusion reactors because of its high melting point, low sputtering yield, high-temperature strength, and low tritium retention properties. On the other hand, Cu and its alloys show excellent thermal conductivity making them ideal as a heat sink material in reactors. Therefore, W-Cu layered composites have important applications in nuclear fusion reactors. Due to the immiscibility between W and Cu, direct alloying between them without using interlayer metals is critical for the preparation of such layered composites. In this study, a nanoporous active structure was used to induce and promote the direct alloying of the W-Cu system. Direct alloying consists of three steps. First, a nanoporous active layer is prepared on the surface of a W foil via two-step anodizing and deoxidized annealing in a hydrogen atmosphere. Second, a Cu coating layer is deposited on the nanoporous W by electroplating. Finally, the obtained W-Cu electrodeposited sample is annealed at temperatures close to the melting point of Cu (i.e., 980oC). The established thermodynamic model for the direct alloying of immiscible metal systems is used for the direct alloying of W and Cu based on a nanoporous active structure. There are two problems with this model. First, the surface energy results are arbitrary due to the selection of the number of surface atomic layers. Second, the unit scale in thermodynamic calculations. To solve these problems, the calculation methods for surface energy and pressure energy are improved in this work, which makes the thermodynamic calculation for the direct alloying of W-Cu based on a nanoporous active structure feasible. The results show that a nanoporous active structure is formed on the surface of W after nanotreatment. The characterization results of the W/Cu interface show that the diffusion distance between the two metals is about 27 nm and the direct alloying between W and Cu is successful. The average shear strength of the W-Cu layered composites was 101 MPa. This is a 16% increase compared with W-Cu layered composites without a nanoporous structure. The thermodynamic calculation results show that the surface energy of the W-Cu system is greatly improved due to the nanoporous active structure prepared on the W surface. The surface energy can be used as the main thermodynamic driving force for the direct alloying of W-Cu systems. There are different reasons why nanotreatment increases W surface energy. One reason is the increase of crystal planes with high surface energy via nanotreatment of the W surface, and another is the shape of the nanoporous structure.

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    Microstructure and Mechanical Properties of Inconel 718 Powder Alloy Prepared by Hot Isostatic Pressing
    XU Lei, TIAN Xiaosheng, WU Jie, LU Zhengguan, YANG Rui
    Acta Metall Sin. 2023, 59 (5): 693-702.   DOI: 10.11900/0412.1961.2021.00586
    Abstract   HTML   PDF (2872KB)

    Inconel 718 alloy, with outstanding high-temperature resistance and mechanical properties, has been widely used in aviation fields. However, large and complex structural components are difficult to produce by traditional processes, which may lead to segregation, micropores, and Laves phases. Net-shape hot isostatic pressing (HIP) is a powder metallurgy processing technology that produces near-shape or net-shape components with the desired microstructures, properties, and cost effectiveness. In this study, Inconel 718 pre-alloyed powder was prepared using the electrode induction melting gas atomization technique, and then the pre-alloyed powder was characterized. Powder compacts were prepared by the HIP of the pre-alloyed powder, and their mechanical properties were tested. Although clean, high-quality powder can be obtained from Inconel 718 alloy due to its lower chemical reactivity compared to titanium alloys, carbide-forming elements diffuse to the powder surface during HIP. These form a hard film with the original oxide particles as nuclei, consisting of Ni3Nb and carbides of Ti and Nb. These films become prior particle boundaries (PPBs) in the obtained powder metallurgy Inconel 718 alloy, resulting in lower ductility, toughness, and stress rupture life than those of the wrought version of the alloy. Suppressing the formation of the PPBs during HIP or eliminating them via subsequent processing significantly improves the comprehensive mechanical properties of the material.

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    Microstructure and Properties of AlCo x CrFeNiCu High-Entropy Alloy Coating Synthesized by Cold Spraying Assisted Induction Remelting
    FENG Li, WANG Guiping, MA Kai, YANG Weijie, AN Guosheng, LI Wensheng
    Acta Metall Sin. 2023, 59 (5): 703-712.   DOI: 10.11900/0412.1961.2021.00285
    Abstract   HTML   PDF (4583KB)

    High-entropy alloy coatings have a very wide range of industrial applications due to their outstanding mechanical properties and good wear resistance. High-entropy alloy coatings of AlCo x CrFeNiCu (x = 0, 0.5, 1.0, 1.5, 2.0, mole fraction) on 45 steel substrates were successfully produced by cold spraying assisted induction remelting approach. The effect of Co content on the phase and microstructure of cold spraying-assisted high-entropy alloy coating was investigated. The findings reveal that the AlCo x -CrFeNiCu high-entropy alloy coating produced using low-pressure cold spraying assisted induction remelting technique comprises of fcc + bcc two-phase mixed structure, with an equiaxed dendrite + interdendritic structure, with the dendrite being bcc and the interdendritic structure being fcc. The lattice distortion state of AlCo x CrFeNiCu high-entropy alloy coating changes as the Co element changes; when x = 1.0, the lattice strain of AlCo1CrFeNiCu high-entropy alloy coating is the largest. Increases in Co content promote an increase in dendrite number in AlCo x CrFeNiCu high-entropy alloy coatings, as well as dendrite. The EDS analysis demonstrated that Fe, Cr, Co, and Ni were enriched in the dendrite, Cu was enriched in the interdendrite, and Al was evenly distributed throughout the coating. With an increase in Co content, the hardness of AlCo x CrFeNiCu high-entropy alloy coating increases first and then decreases. When x = 1.0, the hardness of the AlCo1CrFeNiCu high-entropy alloy coating is 562.5 HV, and the coating minimum's friction coefficient is 0.352.

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