Started in 1988 Monthly
ISSN: 1006-7191
CN: 21-1361/TG
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Institute of Metal Research, Chinese Academy of Science

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Research Progress on the Corrosion Behavior of Magnesium-Lithium-Based Alloys: A Review
Bao-Jie Wang, Ji-Yu Luan, Dao-Kui Xu, Jie Sun, Chuan-Qiang Li, En-Hou Han
Acta Metallurgica Sinica(English letters)    2019, 32 (1): 1-9.   DOI: 10.1007/s40195-018-0847-9
Abstract   HTML PDF (1688KB)  

In this review paper, the research progress on corrosion behavior of hexagonal close-packed (HCP) singular phase, body cubic-centered (BCC) singular phase and (HCP?+?BCC) duplex-structured Mg-Li alloys has been summarized and reviewed, and the future trend about the studies on corrosion behavior of Mg-Li-based alloys and possible solving methods for the improvement in corrosion resistance are discussed also.

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Enhanced Strength and Corrosion Resistance of Mg-2Zn-0.6Zr Alloy with Extrusion
Luan-Xiang Wang, Ren-Bo Song, Chang-Hong Cai, Jing-Yuan Li
Acta Metallurgica Sinica(English letters)    2019, 32 (1): 10-22.   DOI: 10.1007/s40195-018-0793-6
Abstract   HTML PDF (5913KB)  

The microstructure, mechanical properties and corrosion behavior of Mg-2Zn-0.6Zr alloy under the as-cast and as-extruded conditions were investigated. Microstructure analysis indicated the remarkable grain refinement by extrusion, as well as notable reductions in volume fraction and size of precipitate phases. As compared with the as-cast alloy, the as-extruded alloy exhibited better mechanical performance, especially in yield strength which was promoted from 51 to 194 MPa. Refined grains, dispersive precipitate phases and texture were thought to be the main factors affecting the improved performance in strength. The electrochemical measurement and immersion test revealed the corrosion rate of Mg-2Zn-0.6Zr alloy by extrusion decreased from 1.68 to 0.32 mm/year. The reasons for the enhanced corrosion resistance were mainly attributed to the decreased volume fraction and Volta potential of the precipitate phases, the refinement of the grain size, as well as the formation of more protective corrosion film.

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Effect of Prior Cold Deformation on the Stability of Retained Austenite in GCr15 Bearing Steel
Feng Wang, Dong-Sheng Qian, Xiao-Hui Lu
Acta Metallurgica Sinica(English letters)    2019, 32 (1): 107-115.   DOI: 10.1007/s40195-018-0787-4
Abstract   HTML PDF (2146KB)  

In this work, the effect of prior cold deformation on the stability of retained austenite in GCr15 bearing steel was investigated after quenching and tempering treatment. The thermal stability was evaluated by calculating thermal activation energy for decomposition of retained austenite using differential scanning calorimeter. The mechanical stability was investigated according to the strain-induced martensitic transformation behavior of retained austenite under the standard compression testing. It is found that the prior cold deformation not only accelerates the carbide dissolution during the austenitization process but also contributes to the carbon partitioning in the tempering stage due to the higher density of phase boundaries, which results in the improvement of the thermal stability of retained austenite. Due to the enhanced carbide dissolution, the higher carbon content in the prior austenite will intensify the isotropic strain of martensitic transformation. As a consequence, the film-like retained austenite is likely to form under a higher hydrostatic pressure and thus shows a higher mechanical stability. Additionally, it is noteworthy that the benefits of the prior cold deformation to the stability of retained austenite would be saturated when the cold deformation degree is larger than 40%.

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Effect of Heat Treatment on Microstructure and Stress Rupture Properties of a Ni-Mo-Cr-Fe Base Corrosion-Resistant Superalloy
Tao Liu, Mei Yang, Jun-Song Wang, Jia-Sheng Dong, Li Wang, Lang-Hong Lou
Acta Metallurgica Sinica(English letters)    2019, 32 (1): 116-126.   DOI: 10.1007/s40195-018-0837-y
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The influences of heat treatment and test condition on the microstructure and stress rupture properties of a Ni-Mo-Cr-Fe base corrosion-resistant superalloy have been investigated in this paper. Optical microscope and scanning electron microscope were employed for the microstructure observation, and X-ray diffraction, electron probe micro-analyzer, and transmission electron microscope were used for phase determination. It was found that the grain size increased and the volume fractions of initial M6C carbides decreased along with the increase in solution treatment temperature. When tested at 650 °C/320 MPa, the stress rupture lives decreased with the increase in solution treatment temperature, but the stress rupture lives increased slightly at first and then decreased for the samples solution heat treated at 1220 °C when tested at 700 °C/240 MPa. The elongations showed the descendent trends under these two conditions. The stress rupture life and elongation for the aged samples all showed a noticeable improvement at 650 °C/320 MPa, but there was no noticeable improvement at 700 °C/240 MPa. The reasons can be attributed to the grain size, test conditions, and the initial and secondary carbides.

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Cracking Behavior in Additively Manufactured Pure Tungsten
Dian-Zheng Wang, Kai-Lun Li, Chen-Fan Yu, Jing Ma, Wei Liu, Zhi-Jian Shen
Acta Metallurgica Sinica(English letters)    2019, 32 (1): 127-135.   DOI: 10.1007/s40195-018-0752-2
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In this study, near fully dense (96.5%) pure tungsten bulks were additively manufactured and the cracking behavior was investigated. A crack network with a spacing of ~?100 μm was observed in the fabricated bulks. It was observed that the laser scanning strategy, which could tailor the microstructure, affected the crack distribution pattern in fabricated tungsten. The calculated surface temperature difference (7300 K) was much higher than the cracking criterion (800 K) of tungsten, indicating that cracking is almost inevitable in laser additive manufacturing of tungsten. It could be concluded that crack network formed because the cracks emerged in every laser molten track and then interconnected in the layer-by-layer building process.

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Thermal Stability of WB2 and W-B-N Films Deposited by Magnetron Sputtering
Yan?Ming Liu, Tong Li, Feng Liu, Zhi-Liang Pei
Acta Metallurgica Sinica(English letters)    2019, 32 (1): 136-144.   DOI: 10.1007/s40195-018-0864-8
Abstract   HTML PDF (2044KB)  

The work is mainly to study the thermal stability including the phase stability, microstructure and tribo-mechanical properties of the AlB2-type WB2 and W-B-N (5.6 at.% N) films annealed in vacuum at various temperatures, which are deposited on Si and GY8 substrates by magnetron sputtering. For the WB2 and W-B-N films deposited on Si wafers, as the annealing temperature increases from 700 to 1000 °C, a-WB (700 °C) and Mo2B5-type WB2 (1000 °C) are successively observed in the AlB2-type WB2 films, which show many cracks at the temperature ≥?800 °C resulting in the performance failure; by contrast, only slight α-WB is observed at 1000 °C in the W-B-N films due to the stabilization effect of a-BN phase, and the hardness increases to 34.1 GPa first due to the improved crystallinity and then decreases to 31.5 GPa ascribed to the formation of α-WB. For the WB2 and the W-B-N films deposited on WC-Co substrates, both the WB2 and W-B-N films react with the YG8 (WC-Co) substrates leading to the formation of CoWB, CoW2B2 and CoW3B3 with the annealing temperature increasing to 900 °C; a large number of linear cracks occur on the surface of these two films annealed at ≥?800 °C leading to the film failure; after vacuum annealing at 700 °C, the friction performance of the W-B-N films is higher than that of the deposited W-B-N films, while the wear resistance of the WB2 films shows a slight decrease compared with that of the deposited WB2 films.

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A High-Ductility Mg-Zn-Ca Magnesium Alloy
Teng Tu, Xian-Hua Chen, Jiao Chen, Chao-Yue Zhao, Fu-Sheng Pan
Acta Metallurgica Sinica(English letters)    2019, 32 (1): 23-30.   DOI: 10.1007/s40195-018-0804-7
Abstract   HTML PDF (2052KB)  

A new kind of Mg-2Zn-0.6Ca (wt%) alloy was fabricated by casting and hot extrusion as a high-ductility structural material. The extruded alloy exhibits a superior elongation of ~30%, yield strength of 130 MPa and ultimate tensile strength of 280 MPa along the extrusion direction at room temperature. Microstructure, texture and tensile properties of the extruded alloy were investigated in details. The remarkable improvement of ductility is ascribed to the weakened basal texture, refined grains and a small number of second phase in the alloy.

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Strength and Wear Behavior of Mg Alloy AE42 Reinforced with Carbon Short Fibers
Sabbah Ataya, Naser A. Alsaleh, Mohamed M. El-Sayed Seleman
Acta Metallurgica Sinica(English letters)    2019, 32 (1): 31-40.   DOI: 10.1007/s40195-018-0771-z
Abstract   HTML PDF (2539KB)  

In addition to the advantage of the lightweight of magnesium alloys, magnesium composites have moderate strength and elastic modulus. The proposed application of magnesium composites as diesel truck pistons makes it necessary to assess their wear performance. Little research data have been discussed on wear behavior of Mg alloy AE42 matrix and its composites. Thus, this paper reports wear behavior of magnesium alloy AE42 (Mg-Al-Mn—RE; rare earth) and its composite AE42-C, which contains 23 vol% of randomly oriented carbon short fibers. Materials characterization, including density measurements, hardness testing, microstructures investigation, and compression testing at temperatures of 25, 150, and 300 °C, were conducted. Wear tests were performed under various loads and sliding distances. Wear mechanisms were also proposed based on the examination of worn surfaces using optical microscopy and scanning electron microscopy equipped with EDX (energy-dispersive X-ray spectrometry) analysis system. The hardness of AE42-23 vol% C composite is twice the hardness of the Mg matrix alloy AE42. Significant improvements to yield stress and compressive strength at temperatures of 25, 150, and 300 °C of the composite versus the AE42 alloy are achieved. Wear resistance of the composite is improved considerably versus that of the Mg alloy AE42 at the various sliding distances. Smearing of graphite on the worn surface produces a lubricating film that delays change from mild to severe wear of the composite, especially at high loads. EDX analysis of the worn surface shows oxidation of the matrix alloy at higher wear loads, and this mechanism decreases in the presence of carbon fibers under the same loads. Abrasive wear, oxidation, and plastic deformation are the dominant wear mechanisms for the alloy matrix AE42, whereas mainly abrasive wear is the wear mechanism of AE42-23 vol% C composite under the proposed testing conditions.

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Effect of Mo Addition on Corrosion Behavior of High-Entropy Alloys CoCrFeNiMox in Aqueous Environments
Xu-Liang Shang, Zhi-Jun Wang, Qing-Feng Wu, Jin-Cheng Wang, Jun-Jie Li, Jia-Kang Yu
Acta Metallurgica Sinica(English letters)    2019, 32 (1): 41-51.   DOI: 10.1007/s40195-018-0812-7
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The corrosion behavior of CoCrFeNiMox alloys was investigated in aqueous environments, NaCl and H2SO4 solutions, respectively, to simulate typical neutral and acidic conditions. The cyclic polarization curves in NaCl and the potentiodynamic curves in H2SO4 clearly reveal the beneficial effects of Mo and the detrimental effect of σ-phase on the corrosion resistance. The X-ray photoelectron spectroscopy results of CoCrFeNiMox alloys in H2SO4 solution indicate that Cr and Mo predominate the corroded surface of the alloys, where Mo primarily exists in the form of MoO3.

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Microstructural Characterization and Tensile Behavior of Rutile (TiO2)-Reinforced AA6063 Aluminum Matrix Composites Prepared by Friction Stir Processing
Sahayam Joyson Abraham, Isaac Dinaharan, Jebaraj David Raja Selvam, Esther Titilayo Akinlabi
Acta Metallurgica Sinica(English letters)    2019, 32 (1): 52-62.   DOI: 10.1007/s40195-018-0806-5
Abstract   HTML PDF (3894KB)  

Rutile (TiO2) particle-reinforced aluminum matrix composites were prepared by friction stir processing. The microstructure was studied using conventional and advanced characterization techniques. TiO2 particles were found to be dispersed uniformly in the composite. Clusters of TiO2 particles were observed at a higher particle content of 18 vol%. The interface between the TiO2 particle and the aluminum matrix was characterized by the absence of pores and reactive layer. Sub-grain boundaries, ultra-fine grains and dislocation density were observed in the composites. TiO2 particles improved the mechanical properties of the composites. However, a drop in tensile strength was observed at a higher particle content due to cluster formation. All the prepared composites exhibited ductile mode of fracture.

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Novel Crystallization Behaviors of Zr-Based Metallic Glass Under Thermo-Mechanical Coupled Fatigue Loading Condition
Zhi-Chao Ma, Xiao-Xi Ma, Hong-Wei Zhao, Fu Zhang, Li-Ming Zhou, Lu-Quan Ren
Acta Metallurgica Sinica(English letters)    2019, 32 (7): 797-802.   DOI: 10.1007/s40195-019-00882-7
Abstract   HTML PDF (1467KB)  

Novel crystallization behaviors of Zr55Cu30Al10Ni5 bulk metallic glass are investigated. On the one hand, mixed oxides, including CuO, CuAlO2, CuAl2O4 and ZrO2, show sequential oxidation process determined by coupling effects of specific cyclic load and temperature. On the other hand, at a temperature (100°C) by far lower than Tg of 412°C, under cyclic loading condition, non-oxidized binary alloy CuZr2 is precipitated; the thermo-mechanical coupled effects of temperature below Tg and fatigue accumulation on the non-oxidized crystallization behaviors are revealed. Meanwhile, at a constant temperature of 400°C, by comparing among the XRD patterns, respectively, obtained from tensile, creep and fatigue fractures, the dominating effect of cyclic load on the generation of non-oxidized CuZr2 is verified. Furthermore, the crystallization behavior of amorphous phases under cyclic loading condition is observed through TEM micrograph and diffraction pattern at 100°C.

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Atomic Structure of Cu49Hf42Al9 Metallic Glass with High Glass-Forming Ability and Plasticity
Kai Li, Yu-Jen Chou, Fang-Liang Gao, Guo-Qiang Li
Acta Metallurgica Sinica(English letters)    2019, 32 (7): 803-807.   DOI: 10.1007/s40195-019-00907-1
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Electron diffraction was used to study the local atomic structure of Cu49Hf42Al9 metallic glasses (MGs). The amorphous nature of the MG was fully retained after the compression test. The partial radial distribution functions (PRDFs) of the MG structure obtained from the atomic model using reverse Monte Carlo and density functional theory optimization display that the peaks of the first nearest-neighbour distances for Cu-Cu, Hf-Cu and Hf-Hf atomic pairs were located at 2.56 ?, 2.78 ? and 3.23 ?, respectively. The wide distribution of PRDF for Hf-Hf atomic pair explained the high plasticity of the material.

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Effect of Alloying Element on Electromagnetic Interference Shielding Effectiveness of Binary Magnesium Alloys
Zhu Luo, Xian-Hua Chen, Kai Song, Chun-Quan Liu, Yan Dai, Di Zhao, Fu-Sheng Pan
Acta Metallurgica Sinica(English letters)    2019, 32 (7): 817-824.   DOI: 10.1007/s40195-019-00887-2
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The microstructure, electrical conductivity and electromagnetic interference shielding effectiveness of Mg-X (X?=?Al, Sn, Y and Gd) alloys in as-cast and solution states were systematically investigated in this study. The electrical conductivity and electromagnetic shielding capacity of binary magnesium alloys decrease linearly with alloying element content. The electromagnetic shielding effectiveness of the binary magnesium alloys with the same alloying element content is as follows: Mg-Gd?

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Effect of Temperature on Grain Size in AA6063 Aluminum Alloy Subjected to Repetitive Corrugation and Straightening
N. Thangapandian, S. Balasivanandha Prabu , K. A. Padmanabhan
Acta Metallurgica Sinica(English letters)    2019, 32 (7): 835-844.   DOI: 10.1007/s40195-018-0866-6
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The influence of processing temperature on grain size reduction in AA 6063 aluminum alloy subjected to repetitive corrugation and straightening (RCS) is investigated in this work. The aluminum alloy was processed by RCS at different temperatures (room temperature, 100 °C, 200 °C and 300 °C) till the maximum number of passes possible before failure and the mechanical properties such as tensile strength and hardness were measured. The grain size and their misorientation of grains of the processed samples were analyzed using the electron backscattered diffraction. The results indicated that the transformation of low-angle grain boundaries to high-angle grain boundaries and dislocation tangles were highly dependent on the strain imparted, which could be controlled by selecting the proper processing temperature. As a result, the mechanical properties are affected. In particular, the room temperature tensile strength and hardness values of the processed material decrease with increasing processing temperature.

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Tribological Characterization of Commercial Pure Titanium Processed by Multi-Directional Forging
I. Ansarian, M. H. Shaeri, M. Ebrahimi, P. Minárik
Acta Metallurgica Sinica(English letters)    2019, 32 (7): 857-868.   DOI: 10.1007/s40195-019-00877-4
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This work discusses tribological properties of commercial pure (CP) titanium processed by multi-directional forging (MDF) up to six passes at room temperature and 220 °C. For this purpose, wear test was conducted by dry sliding pin-on-disk method on the initial and ultrafine grained samples using different stress magnitudes of 1, 1.5 and 2 MPa. The results showed that wear resistance of CP titanium increases after the first pass of MDF in comparison with the initial condition, irrespective of the applied normal stress. For example, the average wear rate of MDFed samples was decreased about 30% and 24%, after first pass at room temperature and 220 °C, respectively. However, average wear rate of the samples processed by six MDF passes was reduced about 40% at lower normal loads; it was increased about 9% at higher ones as compared to the initial condition. It was also found that the dominated wear mechanisms were abrasive and delaminated at the lower stresses, while the delamination mechanism was intensified and a slight adhesion was observed during the higher applied normal loads.
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Corrosion Evolution of Steel Reinforced Concrete Under Simulated Tidal and Immersion Zones of Marine Environment
Jie Wei, Chang-Gang Wang, Xin Wei, Xin Mu, Xiao-Yan He, Jun-Hua Dong, Wei Ke
Acta Metallurgica Sinica(English letters)    2019, 32 (7): 900-912.   DOI: 10.1007/s40195-018-0867-5
Abstract   HTML PDF (4369KB)  

The corrosion evolution processes of steel reinforced concrete under simulated tidal and immersion zones of marine environment were investigated by using electrochemical measurements and corrosion morphology observations. The results indicate that the corrosion of rebar in concrete under both environments experiences the deterioration from passivation to pitting corrosion and then to general corrosion. Specially, the pitting plays the major role only in the early stage of corrosion, and the general corrosion replaces the dominate role of pitting during the long-term corrosion. In addition, both the pitting depth on local surface and the rust thickness on the overall surface of rebar in the tidal condition are larger than those in immersion condition, which is attributed to the faster corrosion rate in tidal zone caused by the concentrated chloride ions and sufficient oxygen supply.

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Three-Dimensional Growth of Coherent Ferrite in Austenite: A Molecular Dynamics Study
Zhi-Peng Sun, Fu-Zhi Dai, Ben Xu, Wen-Zheng Zhang
Acta Metallurgica Sinica(English letters)    2019, 32 (6): 669-676.   DOI: 10.1007/s40195-019-00889-0
Abstract   HTML PDF (2743KB)  

Coherent second phase often exhibits anisotropic morphology with specific orientations with respect to both the second and the matrix phases. As a key feature of microstructure, the morphology of the coherent particles is essential for understanding the second-phase strengthening effect in various industrial alloys. This letter reports anisotropic growth of coherent ferrite from austenite matrix in pure iron based on molecular dynamics simulation. We found that the ferrite grain tends to grow into an elongated plate-like shape, independent of its initial configuration. The final shape of the ferrite is closely related to the misfit between the two phases, with the longest direction and the broad facet of the plate being, respectively, consistent with the best matching direction and the best matching plane calculated via the Burgers vector content (BVC) method. The strain energy calculation in the framework of Eshelby’s inclusion theory verifies that the simulated orientation of the coherent ferrite is energetically favorable. It is anticipated that the BVC method will be applicable in analysis of anisotropic growth and morphology of coherent second phase in other phase transformation systems.

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High-Speed Friction Stir Welding of SiCp/Al-Mg-Si-Cu Composite
Chen Wang, Bei-Bei Wang, Dong Wang, Peng Xue, Quan-Zhao Wang, Bo-Lv Xiao, Li-Qing Chen, Zong-Yi Ma
Acta Metallurgica Sinica(English letters)    2019, 32 (6): 677-683.   DOI: 10.1007/s40195-018-0833-2
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A 17 vol% SiCp/Al-Mg-Si-Cu composite plate with a thickness of 3 mm was successfully friction stir welded (FSWed) at a very high welding speed of 2000 mm/min for the first time. Microstructural observation indicated that the coarsening of the precipitates was greatly inhibited in the heat-affected zone of the FSW joint at high welding speed, due to the significantly reduced peak temperature and duration at high temperature. Therefore, prominent enhancement of the hardness was achieved at the lowest hardness zone of the FSW joint at this high welding speed, which was similar to that of the nugget zone. Furthermore, the ultimate tensile strength of the joint was as high as 369 MPa, which was much higher than that obtained at low welding speed of 100 mm/min (298 MPa). This study provides an effective method to weld aluminum matrix composite with superior quality and high welding efficiency.

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Effects of Post-weld Heat Treatment on Microstructure, Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints
Deng-Kui Zhang, Guo-Qing Wang, Ai-Ping Wu, Ji-Guo Shan, Yue Zhao, Tian-Yi Zhao, Dan-Yang Meng, Jian-Ling Song, Zhong-Ping Zhang
Acta Metallurgica Sinica(English letters)    2019, 32 (6): 684-694.   DOI: 10.1007/s40195-018-00869-w
Abstract   HTML PDF (5351KB)  

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows different microstructure and microhardness due to the different welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing effect on the weld and their existence was more of an adverse effect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.

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Horizontally Solidified Al-3 wt%Cu-(0.5 wt%Mg) Alloys: Tailoring Thermal Parameters, Microstructure, Microhardness, and Corrosion Behavior
Barros André, Cruz Clarissa, P. Silva Adrina, Cheung Noé, Garcia Amauri, Rocha Otávio, Moreira Antonio
Acta Metallurgica Sinica(English letters)    2019, 32 (6): 695-709.   DOI: 10.1007/s40195-018-0852-z
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In the present experimental investigation, Al-3 wt%Cu and Al-3 wt%Cu-0.5 wt%Mg alloys castings are produced by a horizontal solidification technique with a view to examining the interrelationship among growth rate (GR), cooling rate (CR), secondary dendrite arm spacing (λ2), Vickers microhardness (HV), and corrosion behavior in a 0.5 M NaCl solution. The intermetallic phases of the as-solidified microstructures, that is, θ-Al2Cu, S-Al2CuMg, and ω-Al7Cu2Fe, are subjected to a comprehensive characterization by using calculations provided by computational thermodynamics software, optical microscopy, and scanning electron microscopy/energy-dispersive spectroscopy. Moreover, electrochemical impedance spectroscopy and potentiodynamic polarization tests have been applied to analyze the corrosion performance of samples of both alloys castings. Hall-Petch-type equations are proposed to represent the HV dependence on λ2. It is shown that the addition of Mg to the Al-Cu alloy has led to a considerable increase in HV; however, the Al-Cu binary alloy is shown to have lower corrosion current density (icorr) as well as higher polarization resistance as compared to the corresponding results of the Al-Cu-Mg ternary alloy.

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Microstructure and Texture Evolution During the Direct Extrusion and Bending-Shear Deformation of AZ31 Magnesium Alloy
Xiao-Ye Liu, Li-Wei Lu, Kun Sheng, Tao Zhou
Acta Metallurgica Sinica(English letters)    2019, 32 (6): 710-718.   DOI: 10.1007/s40195-018-0848-8
Abstract   HTML PDF (3568KB)  

AZ31 alloys were extruded by direct extrusion and bending-shear deformation (DEBS). The microstructure characteristic and texture evolution of DEBSed AZ31 sheets were investigated by electron backscattered diffraction (EBSD). It is found that DEBS technique could effectively refine grains and weaken texture. Besides, we also investigate how twinning affects dynamic recrystallization during hot extrusion. {10-12} extension twins can offer nucleation sites and enough energy to trigger dynamic recrystallization. Moreover, the character of direct extrusion and bending-shear die can lead to the activation of non-basal slip system and further dramatically weaken the basal texture of the microstructure with many pre-activated basal slip systems.

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Superparamagnetic CoFe2O4@Au with High Specific Absorption Rate and Intrinsic Loss Power for Magnetic Fluid Hyperthermia Applications
Sandip Sabale, Vidhya Jadhav, Shubhangi Mane-Gavade, Xiao-Ying Yu
Acta Metallurgica Sinica(English letters)    2019, 32 (6): 719-725.   DOI: 10.1007/s40195-018-0830-5
Abstract   HTML PDF (1540KB)  

CoFe2O4 nanoparticles (NPs) and surface modified with gold (Au) have been synthesized by a thermal decomposition method. The obtained NPs and formation of CoFe2O4@Au core-shell (CS) were confirmed by characterizing their structural and optical properties using X-ray powder diffraction (XRD) patterns, Fourier transform infrared spectroscopy, Raman spectroscopy, UV-Visible and photoluminescence studies. Morphological and compositional studies were carried out using high-resolution transmission electron microscopy and energy-dispersive X-ray spectroscopy, while the magnetic properties were determined using alternating gradient magnetometer and Mossbauer to define the magneto-structural effects of shell formation on the core NPs. Induction heating properties of CoFe2O4 and CoFe2O4@Au CS magnetic nanoparticles (MNPs) have been investigated and correlated with magneto-structural properties. Specific absorption rate and intrinsic loss power were calculated for these MNPs within the human tolerable range of frequency and amplitude, suggesting their potential in magnetic fluid hyperthermia therapy for possible cancer treatment.

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Mechanical Relaxation of a Ti36.2Zr30.3Cu8.3Fe4Be21.2 Bulk Metallic Glass: Experiments and Theoretical Analysis
Qiao J.C., Chen Y.H., Lyu G.J., Song K.K., Pelletier J.M., Yao Y.
Acta Metallurgica Sinica(English letters)    2019, 32 (6): 726-732.   DOI: 10.1007/s40195-018-0860-z
Abstract   HTML PDF (2840KB)  

The dynamic mechanical relaxation behavior of Ti36.2Zr30.3Cu8.3Fe4Be21.2 bulk metallic glass with good glass-forming ability was investigated by mechanical spectroscopy. The mechanical relaxation behavior was analyzed in the framework of quasi-point defects model. The experimental results demonstrate that the atomic mobility of the metallic glass is closely associated with the correlation factor χ. The physical aging below the glass transition temperature Tg shows a non-Debye relaxation behavior, which could be well described by stretched Kohlrausch exponential equation. The Kohlrausch exponent \(\beta_{\text{aging}}\) reflects the dynamic heterogeneities of the metallic glass. Both concentration of “defects” and atomic mobility decrease caused by the in situ successive heating during the mechanical spectroscopy experiments.

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Effect of Electric Potentials on Microstructure, Corrosion and Wear Characteristic of the Nitrided Layer Prepared on 2Cr13 Stainless Steel by Plasma Nitriding
Li Yang, Zhang Shang-Zhou, Qiu Jian-Xun, He Yong-Yong, Xiu Jun-Jie, Ye Qian-Wen, Liu Zhong-Li
Acta Metallurgica Sinica(English letters)    2019, 32 (6): 733-745.   DOI: 10.1007/s40195-018-0836-z
Abstract   HTML PDF (3489KB)  

Plasma nitriding is a widely used technology to enhance the surface performance and extend the service life of alloy parts. The current research mainly focuses on the influences of time, temperature, gas type and pressure parameters on nitriding behavior, while fewer studies have been conducted on the electric potential. This paper mainly reports the effect of the electric potential on nitriding behavior. Test conditions were set using cathodic, anodic and floating potentials in a plasma nitriding furnace. 2Cr13 stainless steel was nitrided at 450 °C for 5 h in an NH3 atmosphere. The experimental results show that the nitriding treatment can be well performed under the different electric potentials, but differences exist in microstructures, morphologies and performance results of the modified layers. The thickness and hardness values of the nitrided layer are ranked as follows: cathodic>anodic>floating potential. The anodic nitrided surface has an obvious particle deposition layer composed of nitrides and oxides. Electrochemical and tribological experiments show that the corrosion resistance and wear resistance were significantly improved after a nitriding treatment using the three electric potentials. Moreover, the floating nitriding treatment resulted in the best tribological performance and corrosion resistance.

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Grain Size-Dependent Mechanical Properties of a High-Manganese Austenitic Steel
Wang Xiao-Jiang, Sun Xin-Jun, Song Cheng, Chen Huan, Tong Shuai, Han Wei, Pan Feng
Acta Metallurgica Sinica(English letters)    2019, 32 (6): 746-754.   DOI: 10.1007/s40195-018-0828-z
Abstract   HTML PDF (4046KB)  

The effect of grain size on the mechanical properties of a high-manganese (Mn) austenitic steel was investigated via electron-backscattered diffraction, transmission electron microscope, X-ray diffraction, and tensile and impact tests at 25 °C and - 196 °C. The Hall-Petch strengthening coefficients for the yield strength of the high-Mn austenitic steels were 7.08 MPa mm0.5 at 25 °C, which increased to 14 MPa mm0.5 at - 196 °C. The effect that the grain boundary strengthening had on improving the yield strength at - 196 °C was better than that at 25 °C. The impact absorbed energies and the tensile elongations were enhanced with the increased grain size at 25 °C, while they remained nearly unchanged at - 196 °C. The unchanged impact absorbed energies and the tensile elongations were primarily attributed to the emergence of the micro-twin at - 196 °C, which promoted the cleavage fracture in the steels with large-sized grains. Refining the grain size could improve the strength of the high-Mn austenitic steels without impairing their ductility and toughness at low temperature.

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Effect of Short-Time Aging on the Pitting Corrosion Behavior of a Novel Lean Duplex Stainless Steel 2002
Tian-Yi Sun, Yan-Jun Guo, Yi-Ming Jiang, Jin Li
Acta Metallurgica Sinica(English letters)    2019, 32 (6): 755-763.   DOI: 10.1007/s40195-018-0829-y
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The effect of short-time aging in the temperature range between 400 and 1000 °C on the pitting corrosion behavior and mechanical property of a novel lean duplex stainless steel (LDSS) 2002 was investigated through the potentiostatic critical pitting temperature (CPT) tests and the Charpy impact tests. Both the pitting corrosion resistance and the toughness of aged specimens degraded due to the precipitation of detrimental secondary phases and the most significant reduction of CPT and impact energy emerged at 650 °C concurrently. The CPT of LDSS 2002 specimen aged at 650 °C decreased by 28 °C, and the impact energy dropped from 69 to 29 J/cm2 compared with the solution-annealed sample. Transmission electron microscopy characterization showed that the main precipitates in LDSS 2002 were Cr2N and M23C6 along the ferrite-austenite grain boundaries.

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Microstructural Feature and Evolution of Rapidly Solidified Ni3Al-Based Superalloys
Li Ye-Fan, Li Chong, Wu Jing, Li Hui-Jun, Liu Yong-Chang, Wang Hai-Peng
Acta Metallurgica Sinica(English letters)    2019, 32 (6): 764-770.   DOI: 10.1007/s40195-018-0839-9
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The Ni3Al-based superalloy was rapidly solidified in the form of droplets with varying diameters. The cooling rate (Rc) is a function of diameter (D) of droplet. With the decrease in droplet sizes (increase in the cooling rates), the volume fraction of γ′ + γ eutectic structure increases from 21.31 (D = 1400 μm, Rc = 3.6 × 102 K s-1) to 36.31% (D = 270 μm, Rc = 2.3 × 103 K s-1). Moreover, unimodal size distribution of nano-γ′ exists in the droplets instead of bimodal dual-size distributions of γ′ precipitates that are normal in as-cast alloys.

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Influence of Fe on Microstructure and Mechanical Properties in P-doped Ni-Cr-Fe Alloys
Xin-Tong Lian, Wen-Ru Sun, Xin Xin, Fang Liu, Dan-Dan Zheng
Acta Metallurgica Sinica(English letters)    2019, 32 (6): 771-779.   DOI: 10.1007/s40195-018-0815-4
Abstract   HTML PDF (2572KB)  

The influence of Fe on the microstructure and mechanical properties of P-doped Ni-Cr-Fe alloys has been investigated. Results showed that increasing Fe content refined the dendrite microstructure and enhanced the solubility of P in as-cast alloys. The change of microhardness in different dendrite regions was attributed to the segregation of P atoms in solid solution state, which had strengthening effects. Increasing Fe contents from 15.2 to 60.7 wt% reduced the yield strength and tensile strength but had little influence on the elongation of alloys. The stress rupture life of alloys after heat treatment decreased with the increment of Fe contents, and the failure fracture modes transferred from transgranular to intergranular fracture mode. The change of fracture modes was due to the weakness of grain boundaries caused by the increment of Fe. In addition, the precipitation of M23C6 was believed to be related to the segregation of P toward grain boundaries, which led to the fluctuation of carbon and chromium atoms near the grain boundaries in alloys with low Fe contents. Consequently, the increment of Fe decreased the strength of matrix and changed the existence of P atoms and the precipitates at grain boundaries.

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Synergistic Effect of NaCl and SO2 on the Initial Atmospheric Corrosion of Zinc Under Wet-Dry Cyclic Conditions
Yin Qi, Wang Zhen-Yao, Liu Miao-Ran, Pan Chen
Acta Metallurgica Sinica(English letters)    2019, 32 (6): 780-796.   DOI: 10.1007/s40195-018-0863-9
Abstract   HTML PDF (5890KB)  

The synergistic effect of NaCl and SO2 on the atmospheric corrosion of zinc has been studied at equivalent total but different ratios of molar deposition rate under wet-dry cyclic conditions. The results show that the corrosion rates, corrosion morphologies and the composition of the corrosion products are strongly influenced by the molar deposition rate ratio of NaCl and SO2 (NaCl/SO2). The corrosivity of NaCl and SO2 toward zinc increases in order of SO2<1:3<3:1<NaCl<1:1. The corrosion morphology is patchy corrosion for Group 1:1, while it is pocking corrosion for the other four experimental groups. The corrosion product containing sulfur and chlorine detected on zinc is Gordaite (NaZn4SO4(OH)6Cl·6H2O), which has quite porous structure and was supposed to cause the patchy corrosion tendency of zinc in Group 1:1. In addition, soluble zinc corrosion products, which can inhibit the atmospheric corrosion process of zinc, were found on zinc samples in Groups 1:3 and SO2 and connected to the lower corrosion rates of zinc in these two groups.

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Surface and Subsurface Defects Studies of Dental Alloys Exposed to Sandblasting
Krzysztof Siemek, Mirosław Kulik, Marat Eseev, Mirosław Wróbel, Andrey Kobets, Oleg Orlov, Alexey Sidorin
Acta Metallurgica Sinica(English letters)    2019, 32 (10): 1181-1194.   DOI: 10.1007/s40195-019-00884-5
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The defects created in commercial dental alloys during blasting with alumina particles propelled in compressed air under pressure 0.1 and 0.4 MPa have been studied using positron annihilation spectroscopy, scanning electron microscopy and X-ray diffraction. It was observed that higher pressure causes the increase in roughness and damaged zone range. The type of defects was determined as vacancies on dislocations. The defect concentration decreases with the depth and depends on alloys’ type and applied pressure. The Rutherford backscattering spectroscopy and variable energy positron beam studies indicate shallow alumina deposition in material and show that small pressure of 0.1 MPa is not enough to remove metal surface oxides completely in 60 s in all studied dental alloys.

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ISSN: 1005-0302
CN: 21-1315/TG
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