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

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Review on Research Progress of Steel and Iron Wear-Resistant Materials
In this paper, the development history of iron and steel wear-resistant materials is introduced, and the composition, microstructure, wear property, antiwear mechanism and modification technology of three typical wear resistant materials, namely high manganese steel, high chromium cast iron and high. . .
Acta Metall Sin, 2020 Vol. 56 (4): 523-538    DOI: 10.11900/0412.1961.2019.00370
 
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An Investigation of Interface Bonding Strength of Bimetal Plate Based on the Optimization of Asymmetric Double Cantilever Beam Model PDF (933KB)
2020-09-30
Effect of Spraying Process on Microstructure and Tribological Properties of Ta2O5 in situ Composite Ta-based Nanocrystalline Coatings PDF (1298KB)
2020-09-24
Opportunity and Challenge of Refractory High-Entropy Alloys in the Field of Reactor Structural Materials PDF (1040KB)
2020-09-17
Corrosion fatigue behavior of 316LN stainless steel hollow specimen in high-temperature pressurized water PDF (3457KB)
2020-09-17
MICROSTRUTURE AND PROPERTIES OF TI/TNTZO MULTI-LAYERED MATERIAL BY DIRECT LASER DEPOSITION PDF (4119KB)
2020-09-16
Current Issue More>>
      11 October 2020, Volume 56 Issue 10 Previous Issue   
    Progress in Materials Genome Engineering in China
    SU Yanjing, FU Huadong, BAI Yang, JIANG Xue, XIE Jianxin
    Acta Metall Sin. 2020, 56 (10): 1313-1323.   DOI: 10.11900/0412.1961.2020.00199
    Abstract   HTML   PDF (1951KB)

    Materials genome engineering (MGE) is a frontier technology in the field of material science and engineering, which is well capable to revolutionize the research and development (R&D) mode of new materials, greatly improve the R&D efficiency, shorten the R&D time, and reduce the cost. This paper reviews the progress of MGE in China from the aspects of the fundamental theory and methods, key technology and equipment, the R&D of new materials and related engineering application, talents training, formation and promotion of new concept of material genetic engineering. The paper also looks forward to the future development of MGE in China.

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    Effect of Al on Hardenability and Microstructure of 42CrMo Bolt Steel
    LU Chaoran, XU Le, SHI Chao, LIU Jinde, JIANG Weibin, WANG Maoqiu
    Acta Metall Sin. 2020, 56 (10): 1324-1334.   DOI: 10.11900/0412.1961.2020.00045
    Abstract   HTML   PDF (5761KB)

    42CrMo steel has a good combination of strength and toughness after quenching and tempering treatment, which make it an ideal candidate material for high strength bolt. Nevertheless, with the increase of bolt diameter in wind power field, the hardenability of 42CrMo steel is inadequate to manufacture the high strength bolt with diameter over 36 mm. Recent study indicates that Al addition is an economical and effective way to affect the phase transformation product during quenching process. In order to improve the hardenability of 42CrMo bolt steel, the effect of Al on the hardenability of 42CrMo was investigated by Jominy test and cross section hardness distribution test. OM and SEM were used to analyze the morphology of the grain size; chemical phase analysis test was used to detect the precipitation in Al addition steels; the isothermal transformation diagram (TTT curve) was measured to study the phase transformation of the steels; the three dimensional atom probe (3DAP) was used to analyze the Al distribution in matrix; the tensile and impact toughness properties of Al addition steels were also examined. It was found that the hardenability of 42CrMo bolt steel could be improved significantly by Al-Ti and Al-B addition, the hardness was increased by 6 HRC at the position of 25 mm from quenched end, the center hardness in diameter of 42, 48 and 56 mm was increased by 7, 10 and 14 HRC, respectively. The improvement of hardenability for Al-Ti addition steel can be attributed to the increasing dissolved Al content in the matrix because of the Ti addition, which suppresses the formation of bainite during the quenching process. The hardenability of Al-B addition steel is better than that of Al-Ti addition steel, which can be ascribed to the dissolved Al and B inhibiting the phase transformation of ferrite and pearlite. Moreover, Al can play an important role in increasing dissolved B content by means of AlN formation, in which the dissolved Al dispersive distribution in matrix is favorable to improve the hardenability of 42CrMo steel. Meanwhile, the tensile strength and Charpy V-notch impact energy at -40 ℃ of Al addition steels are adequate to manufacture grade 12.9 high strength bolt.

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    Peritectic Solidification Characteristics and Mechanism of 15CrMoG Steel
    LI Yaqiang, LIU Jianhua, DENG Zhenqiang, QIU Shengtao, ZHANG Pei, ZHENG Guiyun
    Acta Metall Sin. 2020, 56 (10): 1335-1342.   DOI: 10.11900/0412.1961.2020.00002
    Abstract   HTML   PDF (2256KB)

    Cast defects of hypo-peritectic steel such as uneven growth of strand shell, crack formation and oscillation marks formation were found to occur frequently during continuous casting of steels. In industry, measures such as high-basicity casting powder, hot-top mold and reduction of mold cooling strength were usually used in the investigations, but a reasonable explanation for these measures has been lacking. In this work, solidification of 15CrMoG steel at different cooling rates were observed with an ultra high temperature confocal scanning laser microscope. The precipitation of the δ-phase was in a cellular manner when the cooling rates were 5 and 15 ℃/min, whereas it was in a dendrite manner when the cooling rate was increased to 100 ℃/min. Thermodynamic analysis of the peritectic phase nucleation showed that a concentration gradient existed at the L/δ interface during the solidication of initial δ phase which led to an increase in the Gibbs free energy barrier for the nucleation of the peritectic γ phase. As the cooling rate increased, the concentration gradient across the L/δ interface became steeper, resulting in an increase in the nucleation undercooling of the peritectic γ phase. This, in turn, decreased the temperature and increased the peritectic reaction rate. In addition, an increase in the cooling rate led to a change in the mode of peritectic transformation (δγ). A diffusion-controlled δγ transformation occurred due to the progression of planar and cellular interfaces at cooling rates of 5 and 15 ℃/min, respectively. However, a large δγ transformation, which was controlled by the interface process, occurred when the cooling rate was increased to 100 ℃/min. The difference in volume shrinkage of the different modes of peritectic transformation (δγ) led to a discussion of the control mechanism of continuous casting of hypo-peritectic steel.

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    Microstructure and Mechanical Properties of HSLA Steel Containing 1.4%Cu
    DU Yubin, HU Xiaofeng, ZHANG Shouqing, SONG Yuanyuan, JIANG Haichang, RONG Lijian
    Acta Metall Sin. 2020, 56 (10): 1343-1354.   DOI: 10.11900/0412.1961.2020.00012
    Abstract   HTML   PDF (4726KB)

    The Cu bearing high strength low alloy (HSLA) steels exhibit high-strength, high toughness and good weldability, which have been widely used in shipbuilding, offshore structures etc. Due to the extremely poor impact energy when attained peak strength, the Cu bearing HSLA steels are usually used at overaged state, which have a good combination of impact energy and strength. In order to clarify the effect of Cu on mechanical properties especially on the impact energy for HSLA steels at peak ageing state, two HSLA steels without Cu (0Cu) and with 1.4%Cu (1.4Cu), were prepared by vacuum induction melting in this study. The influence of Cu on the microstructure of HSLA steel was investigated by OM, SEM and EBSD. Meanwhile, the Cu-riched clusters were characterized by APT and the mechanical properties were measured by tensile test and impact test. The results show that the Cu is completely solid-solutioned into the matrix after quenching, and there are a great number of Cu-riched clusters precipitated in the matrix and boundaries after tempering. Cu element has no obvious effect on the prior austenite grain size, microstructure and effective grain size of tempered HSLA steel, but has significant influence on the strength and impact energy for tempered HSLA steel. After tempered at 450 ℃, the 1.4Cu steel attained the maximum yield strength (1053 MPa), higher than that of 0Cu steel. It is worth noting that the impact energy of 1.4Cu steel tempered at 450 ℃ is only 24 J at room temperature and the impact fracture is a quasi-cleavage brittle fracture mode dominated by river patterns. However, 0Cu steel exhibits a completely ductile fracture mode dominated by dimples at room temperature and the impact energy is 127 J. The APT results show that both 0Cu and 1.4Cu tempered steels have the segregation of C, Cr, Ni, Mn elements at the lath boundary. Compared with 0Cu steel, there precipitate a great number of Cu-riched clusters at the lath boundary for 1.4Cu steel, which will result in the stress concentration and then promote the crack initiation at the lath boundary. In addition, the Cu-rich clusters precipitated at the lath boundary could prevent the Mo segregated at the lath boundary, which will decrease the bonding energy and then promote the crack propagation along the lath boundary. Besides, the negative effect of strengthening due to the Cu-riched clusters at matrix will also accelerate the crack propagation in the matrix, which will decrease the impact energy of 1.4Cu steel. Therefore, the impact energy of 1.4Cu steel is much lower than that of 0Cu steel at room temperature.

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    The Initial Corrosion Behavior of Carbon Steel Exposed to the Coastal-Industrial Atmosphere in Hongyanhe
    SONG Xuexin, HUANG Songpeng, WANG Chuan, WANG Zhenyao
    Acta Metall Sin. 2020, 56 (10): 1355-1365.   DOI: 10.11900/0412.1961.2020.00010
    Abstract   HTML   PDF (4591KB)

    The atmospheric corrosion of carbon steel is an extensive topic that has been studied by many authors who have proposed many mechanisms and techniques for studying the phenomena involved and have reported long term exposure data in many different regions throughout the world. However, there are few literatures that have discussed the corrosion results of carbon steel exposed for short-term time which can contribute to the understanding of the initial corrosion mechanisms. Therefore in this work, mass-loss measurement, SEM, XRD, infrared spectroscopy and electrochemical techniques have been used to investigate the initial corrosion evaluation of carbon steel exposed to a coastal-industrial atmospheric environment in Hongyanhe. Mass-loss results show that the short-term corrosion kinetic of carbon steel is in good fitting with linear function, and the average corrosion rate fluctuates over time and don't show the downward trend observed in long-term exposure experiments. Lepidocrocite, goethite and magnetite are identified in corrosion products formed on the surface of exposed carbon steel samples. The content of lepidocrocite shows a decreasing trend over exposure time, while goethite is the opposite. Magnetite appears in the later stages and keeps stable in amount. Pitting and an irregular localized corrosion can be observed clearly on the surface of carbon steel specimens exposed for 10 d. The corrosion product at pitting regions is circular flowery shape which varies in details as the physical and chemical environments change. The rust layer grows over time and eventually covers the entire surface of carbon steel samples exposed for more than 60 d, yet its thickness is uneven. The surface of rust layer has many nest-shaped structures that can't barricade the physical transmission effectively. The protective effect of rust layer has been further discussed in combination with electrochemical results.

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    Corrosion Behaviors and Mechanisms of ODS Steel Exposed to Static Pb-Bi Eutectic at 600 and 700 ℃
    BAO Feiyang, LI Yanfen, WANG Guangquan, ZHANG Jiarong, YAN Wei, SHI Quanqiang, SHAN Yiyin, YANG Ke, XU Bin, SONG Danrong, YAN Mingyu, WEI Xuedong
    Acta Metall Sin. 2020, 56 (10): 1366-1376.   DOI: 10.11900/0412.1961.2020.00035
    Abstract   HTML   PDF (3522KB)

    With good neutron properties, anti-irradiation performances, heat transfer properties and inherent safety characteristics, liquid lead or Pb-Bi eutectic (LBE) has been a primary candidate coolant for accelerator driven system and advanced nuclear reactors. However, corrosion of structural materials is a critical challenge in the use of liquid lead and LBE in high temperature nuclear reactors. Therefore, research on corrosion compatibility of structural materials with LBE at elevated temperatures is of great significance. In this work, the long-term corrosion experiments in static LBE for a oxide dispersion strengthened (ODS) steel were carried out at 600 and 700 ℃. The temperature effects on different corrosion behaviors were studied by the analyses of XRD, SEM and EDS, and the underlying mechanisms were clarified. After exposing to LBE at 600 ℃ for up to 2000 h, a typical double-layer oxide scale with the thickness of about 10 μm was formed on the surface of ODS steel, which was composed of outer layers of Pb-Fe-O and Fe3O4 and inner layer of Fe-Cr-Al spinal. In addition, a thin Al-rich layer was also formed under the inner layer. Due to the protective effect of the relatively dense inner layer and the Al-rich layer, ODS steel showed excellent resistance to LBE corrosion at 600 ℃ with a significantly lower corrosion rate. On the contrary, when exposed to LBE at 700 ℃ , the structure and thickness of the oxide scale formed on the surface of the ODS steel were obviously different. After exposure for 100 h, a dense protective Al2O3 oxide layer with a thickness of about 500 nm was formed, greatly reducing the corrosion rate. With the corrosion time prolonging to 500 h at 700 ℃, most of Al2O3 layer was still remained. However, a few of nodular-like oxides were formed originated from local weak areas, which broken off the continuity of protective Al2O3 and led to deeper corrosion by LBE.

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    Characteristics of Waterjet Cavitation Erosion of 304 Stainless Steel After Corrosion in NaCl Solution
    LIU Haixia, CHEN Jinhao, CHEN Jie, LIU Guanglei
    Acta Metall Sin. 2020, 56 (10): 1377-1385.   DOI: 10.11900/0412.1961.2020.00107
    Abstract   HTML   PDF (1970KB)

    The 304 stainless steel specimens were corroded in 3%NaCl solution, and then cavitation erosion experiments were performed on these specimens using an experimental rig that conformed to the ASTM G134 standard. The effects of both the corrosion time and erosion time on cavitation erosion were analyzed. The cavitation erosion characteristics were described via the mass loss, surface microstructure, three-dimensional surface morphology and microhardness. The results show that for the specimen corroded for 24 h, the stage of cavitation erosion attenuation commences at the cavitation erosion time of 120 min. In the early stage of cavitation erosion, erosion pits manifest small size and depth. In the later stage of cavitation erosion, the plastic deformation is intensified and large erosion pits are abundant. Microcracks expand along grain boundaries. Eventually, the interconnection between erosion pits incurs peeling-off of grain boundaries. The surface roughness increases with the cavitation erosion time. Compared to the corroded specimens, the non-corroded specimen demonstrates higher surface roughness after cavitation erosion. As the corrosion time increases from 24 h to 120 h and the cavitation erosion time is remained at 120 min, the plastic deformation is strengthened and microcracks emerge at grain boundaries. The 3%NaCl solution helps to suppress cavitation erosion. Nevertheless, as the corrosion time increases, the suppression effect attenuates.

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    In Situ Study on Liquid-Solid Electromigration Behavior in Cu/Sn-37Pb/Cu Micro-Interconnect
    ZHANG Zhijie, HUANG Mingliang
    Acta Metall Sin. 2020, 56 (10): 1386-1392.   DOI: 10.11900/0412.1961.2020.00009
    Abstract   HTML   PDF (2003KB)

    Electromigration (EM), which describes the mass transport due to momentum exchange between conducting electrons and diffusing metal atoms under an applied electric field, has become a serious reliability issue in high-density packaging. With the increasing demands for miniaturization, liquid-solid (L-S) EM will pose a critical challenge to the reliability of solder interconnects. In this work, synchrotron radiation real-time imaging technology is used to in situ study the interfacial reaction and atom migration in Cu/Sn-37Pb/Cu solder interconnects undergoing L-S EM at 185 ℃ with a current density of 1.0×104 A/cm2. In the heating stage, Pb atoms directionally migrate from the cathode toward the anode, resulting in the growth of Pb-rich phase at the anode. In the dwelling stage, Pb atoms diffuse backward, then equilibrium phase is obtained. In the cooling stage, Pb atoms directionally migrate from the cathode toward the anode again until the solder solidified, three phases is obtained: the Pb-rich phase, the Sn-Pb phase and the Sn-rich phase. The abnormal migration behavior of Pb atoms in different stages is determined by the combined effect of the chemical potential gradient flux (Jchem) and EM-induced flux (Jem). Jem is determined by the effective charge number (Z*) of Pb atoms, which was calculated to be -3.20 at 185 ℃ based on the growth kinetics of the Pb-rich layer model.

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    Fabrication of Nanoporous PtRuFe by Dealloying Amorphous Fe(Pt, Ru)B Ribbons and Their Methanol Electrocatalytic Properties
    XU Xiuyue, LI Yanhui, ZHANG Wei
    Acta Metall Sin. 2020, 56 (10): 1393-1400.   DOI: 10.11900/0412.1961.2020.00028
    Abstract   HTML   PDF (2707KB)

    The growing technological demand for high-efficiency direct methanol fuel cells (DMFCs) drives the exploration of catalysts with improved catalytic performance. Conventional pure Pt with good catalytic activity for methanol oxidation reaction (MOR) have been applied in the DMFCs for several decades, while their CO tolerance still needs to be further enhanced. Formation of nanoporous structure with a high specific surface area is an effective way to increase the catalytic efficiency by providing more active sites. Alloying suitable Fe and Ru into Pt is promising for the improvements of both catalytic activity and anti-CO poisoning. In this work, the nanoporous alloys have been fabricated by dealloying Fe65Pt10-xRuxB25 (x=0, 2, 4, atomic fraction, %) melt-spun alloy ribbons in 0.1 mol/L H2SO4 solution, and the phase structures, morphologies, chemical compositions, and magnetic properties of the melt-spun ribbons and nanoporous alloys were characterized by XRD, TEM, SEM, EDS, XPS and VSM, respectively. The electrocatalytic properties for MOR of the nanoporous alloys were examined by cycle voltammetry in 0.5 mol/L H2SO4+1.0 mol/L CH3OH solution. The results reveal that all melt-spun ribbons are fully amorphous, and nanoporous (Pt, Ru)Fe with a single-fcc phase can be obtained after dealloying. The nanoporous (Pt, Ru)Fe dealloyed from x=0 and 2 precursors possess a similar fine bicontinuous ligament/channel structure with average pore diameter and ligament size of 6~7 and 7~8 nm, respectively. Cracks can be found on the surficial nanoporous architecture for the nanoporous PtRuFe obtained from the x=4 alloy. With enriching of Ru, the oxidation peak potential of the nanoporous alloys exhibits a negative shift, and the ratio (jf/jb) of the peak current density in the forward scan (jf) to that in the backward scan (jb) increases gradually. The jf and jf/jb for the nanoporous PtRuFe dealloyed from the x=2 alloy is 0.87 mA/cm2 and 4.6, which are 1.7 and 2.7 times of those for the nanoporous PtFe, respectively, indicating the superior electrocatalytic activity for MOR and CO tolerance in comparison with the binary PtFe alloy. The improvement in electrocatalytic performance after Ru addition can be attribute to the combination of Pt/Ru bifunctional mechanism and weakened Pt-COads adsorption energy. In addition, the nanoporous PtRuFe alloys also exhibit ferromagnetic characteristic with saturation magnetization values of 0.41~0.42 T, which can be easily separated and recycled in the practical applications. This work paves the way for the development of high-performance MOR electrocatalyst.

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    Hot Deformation Characteristics of Novel Wrought Superalloy GH4975 Extruded Rod Used for 850 ℃ Turbine Disc
    ZHANG Yong, LI Xinxu, WEI Kang, WAN Zhipeng, JIA Chonglin, WANG Tao, LI Zhao, SUN Yu, LIANG Hongyan
    Acta Metall Sin. 2020, 56 (10): 1401-1410.   DOI: 10.11900/0412.1961.2020.00074
    Abstract   HTML   PDF (3699KB)

    With the development of aero-engine in the direction of high thrust ratio, high efficiency and high reliability, the indicators of temperature resistance of cast & wrought superalloys are getting higher and higher. For the demand of aero-engine, the wrought superalloy materials used for aero engine turbine disc have been made remarkable progress. Form heat-resistant steel which temperature capability reaches 550 ℃ to iron-nickel based superalloy used at 650 ℃, and the high alloyed wrought superalloy with service temperature of 750 ℃ have been developed. The nickel-based wrought superalloy GH4975 is a high strength, complex alloying, hard-deformed wrought turbine disc alloy, which can be used at 850 ℃. In the study, the thermal deformation behavior of GH4975 extruded rod prepared by vacuum induction melting (VIM) and vacuum arc remelting (VAR) was studied by thermal simulation machine with the temperature range of 1070~1220 ℃ and strain rate range of 0.001~1 s-1. The results show that the stress-strain curves of GH4975 alloy are divided into three stages: strain hardening, flow softening and steady state rheology, exhibiting typical dynamic recrystallization characteristics. The constitutive equation of GH4975 extruded rod was established and the hot deformation activation energy was calculated as 664587 J/mol. Besides, the processing maps of GH4975 alloy were drawn based on the dynamic material model (DMM), and the suitable processing parameters are determined by combining with microstructure observation. The dynamic recrystallization easily occurs at the deformation temperature range of 1100~1130 ℃, and the nucleation mechanisms were elaborated to be strain inducing grain boundary.

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    Influence of White Spot Defects on Microstructure and Mechanical Property of the GH4586 Alloy
    TAN Haibing, HUANG Shuo, WANG Jing, LI Shu, ZHU Changhong, ZHONG Yan, ZHONG Shilin, HE Aijie
    Acta Metall Sin. 2020, 56 (10): 1411-1422.   DOI: 10.11900/0412.1961.2020.00081
    Abstract   HTML   PDF (4289KB)

    GH4586 is a nickel-based wrought superalloy developed by China, and features high Ti, W, Mo and low Al. However, it is easy to form whit spot (WP) defects within the disk components manufactured from the GH4586 ingot with a diameter of 508 mm produced by double vacuum melting method. In present work, the macro- and micro-structural characteristics, as well as the element distribution of WP defect were systematically studied. Special attention was focused on the effects of WP on mechanical properties. Hardness, tensile properties and fracture morphology of normal and defective areas were investigated for comparison. In addition, the formation mechanism and control method of WP defects were investigated based on the thermodynamic calculation and solidification simulation, respectively. In order to analyze its dendritic segregation and second phase precipitation in the solidification process, solidification phase diagram and thermodynamic equilibrium phase diagram of GH4586 alloy were calculated with JmatPro software. To study the forming mechanism of WP, the solidification process of vacuum introduction melting (VIM) GH4586 ingots was simulated with Procast software. Results show that the WP defects within GH4586 components are dendritic WP which exhibits dendritic pattern on the macro level. While on micro level, it is the precipitate clusters which consisted of MC carbides, M6C carbides and large incoherent γ′ phase. Due to the clusters' inherent rigid and fragile characteristics, the tensile strength and ductility of the alloy are significantly reduced. Therefore, the WP defects are harmful to the mechanical properties of the GH4586 disk significantly. The WP defects must be avoided during the forging process. Since excessive internal stress and shrinkage cavities form during the solidification process of large VIM GH4586 ingots, chips fall into molten pool easily if the VIM ingots are employed as vacuum arc remelting (VAR) electrode, and then give birth to WP defects within the final forging components. Therefore, it is the effective method for avoiding WP defects by improving the quality of VAR electrode and optimizing the VAR process.

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    Effect of Al Content on Microstructure and Mechanical Properties of Mg-Sn-Ca Alloy
    WU Huajian, CHENG Renshan, LI Jingren, XIE Dongsheng, SONG Kai, PAN Hucheng, QIN Gaowu
    Acta Metall Sin. 2020, 56 (10): 1423-1432.   DOI: 10.11900/0412.1961.2020.00086
    Abstract   HTML   PDF (3084KB)

    There is considerable demand for high-performance, low-cost, and rare-earth-free magnesium alloys in several industrial applications because of their energy conservation potential. However, the mechanical properties of the currently available rare-earth-free magnesium alloys cannot satisfy the industrial requirements. Therefore, a novel rare-earth-free magnesium alloy with high strength, excellent ductility, and good formability must be urgently developed. In this study, the microstructure and mechanical properties of the Mg-2.5Sn-2Ca-xAl (x=2, 4, and 9, mass fraction, %) alloys in the as-cast and extruded states when different amounts of Al content are added are systematically studied. As indicated by the results, the strength and elongation of the alloy decrease and increase, respectively, with the increasing Al content. The yield strengths of the Mg-2.5Sn-2Ca-2Al, Mg-2.5Sn-2Ca-4Al, and Mg-2.5Sn-2Ca-9Al alloys are approximately 370, 325, and 290 MPa, respectively, and their elongations are approximately 6.2%, 11.0%, and 12.0%, respectively. The type and content of the nanosecond phase of the Mg-Sn-Ca-based alloy changed because of the addition of the fourth type of Al element. High-density G.P. zones and a second phase of Mg17Al12 can be observed in the extruded Mg-2.5Sn-2Ca-2Al and Mg-2.5Sn-2Ca-9Al alloys, respectively; however, nanophase precipitation cannot be observed in case of the extruded Mg-2.5Sn-2Ca-4Al alloy. The high-density G.P. zones hinder the growth of the recrystallized grains more efficiently than the Mg17Al12 nanophase; thus, the recrystallized grains of the extruded Mg-2.5Sn-2Ca-2Al alloys are finer (approximately 0.5 μm) than the extruded Mg-2.5Sn-2Ca-9Al alloy. Based on TEM images, high-density dislocations can be observed inside the extruded Mg-2.5Sn-2Ca-2Al alloy grains and G.P. zones can be observed toward the side of the dislocations; thus, the high density subgrain lamella structure is retained in the alloy (lamella thickness: 0.2~1.0 μm). The movement of the newly generated dislocations is inhibited by the large number of G.P. zones and residual dislocations, increasing the yield strength and decreasing the plasticity of the Mg-2.5Sn-2Ca-2Al alloy. The Mg17Al12 nanophase that was formed in the Mg-2.5Sn-2Ca-9Al alloy because of the addition of high Al content exhibits a weak ability to hinder the movement of the dislocations, resulting in low-density residual dislocation. Therefore, the Mg-2.5Sn-2Ca-9Al alloy, exhibits a large grain size, low yield strength and high plasticity.

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    Effects of Al Interlayer and Ni(V) Transition Layer on the Welding Residual Stress of Co/Al/Cu Sandwich Target Assembly
    JIANG Lin, ZHANG Liang, LIU Zhiquan
    Acta Metall Sin. 2020, 56 (10): 1433-1440.   DOI: 10.11900/0412.1961.2020.00060
    Abstract   HTML   PDF (1448KB)

    Sputtering has been widely used to prepare thin film due to its good cohesion with substrate, high purity, compactness, repeatability and large area manufacture. Target is a key consumable material during production of thin film by sputtering. Generally, targets are mostly rare and high purity metal, so the cost of target is very high. In order to reduce the cost of target, to improve its stiffness, and to enhance the electrical and thermal conductivity, target is usually connected with backplane to form the target assembly. The main connection method is diffusion welding, which is used in the industrial production. However, the target and the backplane are usually two different materials with different physical properties such as coefficient of thermal expansion (CTE) and thermal conductivity. During the welding or soldering process of target, the mismatch of physical properties will lead to residual stress in target, which has a direct influence on the thickness and microstructure uniformity of the films. Hence, it is very meaningful to investigate the residual stress in target and to study its influencing factor. Based on the Co/Al/Cu sandwich structure of backplane diffusion welding, the effects of Al interlayer and Ni(V) layer on welding residual stress were studied by finite element method. It was found that the application of the Al interlayer not only can make diffusion welding process easier and lower the diffusion welding temperature, but also can reduce the maximum residual stress from 142 MPa to 126 MPa. Furthermore, the location of the maximum residual stress also changes from the outer edge of the interface between target and backplane to the position near the symmetrical axis of target and Co/Al interface. Furthermore, there is an optimal thickness for Al interlayer (7 mm). Although the existence of Ni(V) layer can inhibit the generation of brittle intermetallic compounds at the interface of Co/Al and Cu/Al, it also increases the residual stress. Moreover, we find that the increase of residual stress with Ni(V) layer at only Co/Al interface, is smaller than that of adding Ni(V) layer at both Co/Al and Cu/Al interfaces.

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