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Effects of surface roughness on bending properties of rolled AZ31 alloy

Journal of Magnesium and Alloys 2023年第4期11卷 1224-1235页

作者： Gyo Myeong lee Jong Un lee Sung hyuk Park School of Materials Science and Engineering Kyungpook National UniversityDaegu 41566Republic of Korea

This study investigated the effects of mechanical-polishing-induced surface roughness and the direction of polishing lines on the bending properties of a rolled AZ31 *** this end,three-point bending tests were performed on one sample without polishing lines(SS sample)and two samples with polishing lines—one in which the polishing lines were parallel to the rolling direction(RS-RD sample)and the other in which they were parallel to the transverse direction(RS-TD sample).In all three samples,macrocracks were formed in the width direction on the outer surface,where tensile stress was predominantly generated in the longitudinal ***,the macrocracks formed in the SS sample were curved because of the merging of uniformly formed fine microcracks,whereas those formed in the RS-TD sample were linear owing to the formation of relatively coarse microcracks along the polishing *** bendability of the samples was in the order of SS>RS-RD>RS-TD,and their limiting bending depths were 4.8,4.6,and 4.4 mm,*** the presence of mechanical-polishing-induced surface roughness,polishing lines perpendicular to the direction of the major stress(i.e.,tensile stress along the longitudinal direction)resulted in a greater degree of stress concentration on the outer surface of the bending *** higher stress concentration promoted the formation of undesirable{10–11}contraction and{10–11}–{10–12}double twins—which typically act as crack initiation sites—and thereby facilitated crack generation and ***,the surface roughness caused premature fracture during bending deformation,which,in turn,caused deterioration of the bendability of the rolled Mg alloy.

关键词： AZ31 alloy Bending Surface roughness Stress concentration Crack

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Microstructural evolution of pre-twinned Mg alloy with annealing temperature and underlying boundary migration mechanism

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Journal of Magnesium and Alloys 2023年第8期11卷 2953-2966页

作者： Ye Jin kim Jong Un lee Gyo Myeong lee Sung hyuk Park School of Materials Science and Engineering Kyungpook National UniversityDaegu 41566Republic of Korea

This study investigates the variations in the microstructural characteristics of a pre-twinned Mg alloy with the temperature of the subsequent annealing *** this end,a rolled AZ31 alloy is compressed to 3%plastic strain along the rolling direction(RD)to activate{10-12}twinning and is subsequently annealed at 200,250,300,350,and 400℃.Numerous{10-12}twins are formed throughout the compressed material,leading to the formation of a RD-oriented *** an annealing temperature of 200℃,no microstructural variations occur during *** the annealing temperature increases from 250 to 400℃,the residual strain energy and remaining twin boundaries of the annealed material decrease owing to the promoted static recovery and the increased area fraction of twin-free grown ***,an increase in the annealing temperature results in a gradual microstructural transition from a fully twinned grain structure to a completely twin-free grain *** microstructural evolution during annealing is predominantly governed by the movement of high-angle grain boundaries via a strain-induced boundary migration mechanism,and a few twin boundaries migrate above 350℃ because of their lower boundary *** boundary migration behavior and resultant microstructural evolution are discussed in detail based on the variations in boundary mobility and driving force for boundary migration with annealing temperature.

关键词： Rolled Mg alloy {10-12}twin Grain growth Boundary migration Annealing

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Schottky barrier modulation of bottom contact SnO_(2) thin-film transistors via chloride-based combustion synthesis

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Journal of Materials Science & Technology 2023年第17期148卷 199-208页

作者： Bongho Jang Junhee lee Hongki Kang Jaewon Jang hyuk-Jun Kwon Department of Electrical Engineering and Computer Science DGISTDaegu 42988South Korea School of Electronic and Electrical Engineering Kyungpook National UniversityDaegu 41566South Korea School of Electronics Engineering Kyungpook National UniversityDaegu 41566South Korea Convergence Research Advanced Centre for Olfaction DGISTDaegu 42988South Korea

The enhanced carrier flow at the interface between Au and SnO_(2)semiconductors,which initially form Schottky contacts,is realized using chloride-based combustion ***-based combustion sys-tems can achieve chlorine(Cl)doping effects as well as conversion to crystalline SnO_(2)films at clearly lower temperatures(∼250℃)than conventional *** to the Cl doping effect,the high carrier concentration can induce thin potential barriers at the metal/semiconductor(MS)junctions,resulting in carrier injection by *** a result,compared to conventional SnO_(2)thin-film transistors,the de-vices fabricated by combustion synthesis exhibit significantly improved electrical performance with field-effect mobility of 6.52 cm 2/Vs(∼13 times),subthreshold swing of 0.74 V/dec,and on/offratio of∼10^(7)below 300℃.Furthermore,because of the enhanced tunneling carriers induced by the narrowed barrier width,the Schottky barriers are significantly reduced from 0.83 to 0.29 eV(65%decrease)at 250℃and from 0.42 to 0.17 eV(60%decrease)at 400℃.Therefore,chloride-based combustion synthesis can con-tribute to developing SnO_(2)-based electronics and flexible devices by achieving both high-quality oxide films and improved current flow at the MS interface with low-temperature annealing.

关键词： SnO_(2) Combustion Sol-gel Schottky contact Thin-film transistors

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Production of high-purity Mg metal from dolomite through novel molten salt electrolysis and vacuum distillation

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Journal of Magnesium and Alloys 2023年第4期11卷 1308-1320页

作者： Hyeong-Jun Jeoung Tae-hyuk lee Jin-Young lee Kyung-Woo Yi Jungshin Kang Korea Institute of Geoscience and Mineral Resources 124 Gwahak-ro Yuseong-guDaejeon 34132Republic of Korea Department of Materials Science and Engineering Seoul National University1 Gwanak-roGwanak-guSeoul 08826Republic of Korea Department of Resources Engineering University of Science and Technology217 Gajeong-ro Yuseong-guDaejeon 34113Republic of Korea School of Materials Science and Engineering Pusan National University2 Busandaehak-roGeumjeong-guBusan 46241Republic of Korea

In this study,a novel Mg production process for producing high-purity Mg metal from dolomite was *** the electrolysis of calcined dolomite was conducted using Cu cathode and C anode in MgF_(2)–LiF molten salt at 1083–1173 K by applying an average current of 1.42–1.46 A for 9.50–21.0 h,the current efficiency of 66.4–88.6%was *** produced Mg alloys consisted of MgCu_(2)and Cu(Mg)or MgCu_(2)and CuMg_(2)phases,depending on the Mg concentration in the Mg *** the electrolysis of calcined dolomite was conducted in MgF_(2)–LiF–CaF_(2)molten salt at 1083 K,the current efficiency was 40.9–71.4%,owing to undesired reactions such as electroreduction of Ca^(2+)or/and CO_(3)^(2−)***,the current efficiency increased from 40.9%to 63.2%by utilizing a Pt anode,because the occurrence of CO_(3)^(2−)ions in the molten salt was *** vacuum distillation of the obtained Mg alloys at 1300 K for 10 h,Mg metal with a purity of 99.9996–99.9998%was ***,the feasibility of this novel process for the production of high-purity Mg metal from dolomite was demonstrated.

关键词： High-purity magnesium Dolomite Magnesium oxide Electrolytic process Copper metal cathode Vacuum distillation

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Effects of Sn addition on the microstructure and mechanical properties of extruded Mg-Bi binary alloy

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Journal of Magnesium and Alloys 2022年第3期10卷 920-931页

作者： Sang-Cheol Jin Jong Un lee Jongbin Go Hui Yu Sung hyuk Park School of Materials Science and Engineering Kyungpook National UniversityDaegu 41566South Korea Department of Materials Science and Engineering Kyoto UniversityYoshida-honmachiSakyo-kuKyoto606-8501Japan School of Materials Science and Engineering Hebei University of TechnologyTianjin 300130China

We investigated the effects of Sn addition on the microstructural characteristics and mechanical properties of an extruded Mg-Bi binary alloy by comparing Mg-5 Bi(B5)and Mg-5 Bi-4 Sn(BT54).Both the extruded alloys exhibit a partially recrystallized grain structure with a strong extrusion fiber texture and numerous Mg3Bi2 ***,the addition of Sn significantly decreases the average grain size of the extruded alloy from 123.9 to 75.2μ*** Sn solute atoms inhibit the activity of dislocation slip,which reduces the internal strain energy accumulated in the dynamically recrystallized(DRXed)grains during ***,this reduced strain energy leads to the decrease in the DRXed grain size owing to weakened grain growth during natural *** extruded BT54 alloy exhibits higher tensile strength and ductility than the extruded B5 *** improvement in the strength by the Sn addition is attributed to the combined effects of grain refinement,Sn solute atoms,and increased dislocation *** formation of{10-11}and{10-11}-{10-12}twins during tension is suppressed by the grain refinement,thereby improving the tensile elongation considerably.

关键词： Mg±Bi alloy Extrusion Dynamic recrystallization Microstructure Mechanical properties.

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Improvement in tensile strength of extruded Mg-5Bi alloy through addition of Sn and its underlying strengthening mechanisms

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Journal of Magnesium and Alloys 2022年第11期10卷 3100-3112页

作者： Sang-Cheol Jin Jae Won Cha Jeong Hun lee Taekyung lee Sang-Ho Han Sung hyuk Park School of Materials Science and Engineering Kyungpook National UniversityDaegu 41566Republic of Korea Ulsan Regional Division Korea Institute of Industrial TechnologyUlsan 44413Republic of Korea School of Mechanical Engineering Pusan National UniversityBusan 46241Republic of Korea Department of Materials Analysis Korea Institute of Materials ScienceChangwon 51508Republic of Korea

Through an investigation of the microstructure and mechanical properties of extruded Mg–5Bi–x Sn(BT5x, x = 0, 2, 4, and 6 wt%) alloys,this study demonstrates that the addition of Sn to an Mg–5Bi binary alloy significantly improves the tensile strength of the extruded *** the extruded alloys exhibit a typical basal fiber texture and a partially dynamically recrystallized(DRXed) microstructure consisting of fine DRXed grains and coarse un DRXed grains. As the Sn content increases from 0 wt% to 6 wt%, the average size of the DRXed grains decreases from 4.2 to 2.8 μm owing to the increase in the amount of precipitates via their grain-boundary pinning effect. The extruded B5 and BT52 alloys contain numerous Mg_(3)Bi_(2) precipitates, but their size and number density are smaller and higher, respectively, in the latter *** Mg_(2)Sn precipitates as well as Mg_(3)Bi_(2)precipitates are present in the extruded BT54 and BT56 alloys, and the number density of the Mg_(2)Sn precipitates is higher in the latter alloy because of its higher Sn content. The addition of 2 wt% Sn to the B5 alloy significantly improves the yield strength(YS) and ultimate tensile strength(UTS) of the extruded alloy—by 76 and 57 MPa, respectively. This drastic improvement is the combined outcome of enhanced grain-boundary hardening, precipitation hardening, and solid-solution hardening effects induced by the refined DRXed grains, numerous precipitates, and Sn solute atoms, respectively. The further addition of 2 wt% or 4 wt% Sn to the BT52 alloy leads to moderate increments in the YS and UTS of the extruded alloy. Specifically, each addition of 2 wt% Sn increases the YS and UTS by ~26 and ~20 MPa, respectively, which is attributed mainly to the additional precipitation hardening effect induced by the Mg_(2)Sn precipitates.

关键词： Mg-Bi-Sn alloy Extrusion Precipitation Microstructure Tensile property

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Variations in microstructure and bending formability of extruded Mg–Al–Zn–Ca–Y–MM alloy with precompression and subsequent annealing treatment conditions

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Journal of Magnesium and Alloys 2022年第9期10卷 2475-2490页

作者： Jong Un lee Sang-Hoon kim Dong Hee lee Hyun Ji kim Young Min kim Sung hyuk Park School of Materials Science and Engineering Kyungpook National UniversityDaegu 41566Republic of Korea Agency for Defense Development Daejeon 34186Republic of Korea Implementation Research Division Korea Institute of Materials ScienceChangwon 51508Republic of Korea

In this study, the bending formability of an extruded Mg–9Al–1Zn–0.3Mn–0.9Ca–0.6Y–0.5 MM(AZXWMM91100, wt%) alloy at room temperature is significantly improved through application of a combined precompression and subsequent annealing(PCA) treatment. As the amount of precompression applied along the extrusion direction(ED)(i.e., the total strain) increases from 4% to 6%, the area fraction of ED-oriented grains of the PCA-treated alloy increases, which consequently causes an improvement in its bending formability because these grains accommodate larger tensile strain along the ED during bending. As the temperature of the subsequent annealing treatment increases from 350 ℃ to 450 ℃, both the area fraction of the ED-oriented grains and the average grain size increase, and the residual dislocation density decreases owing to the promotion of boundary migration and occurrence of the recovery process at higher ***, the bending formability of both the 4%-precompressed and the 6%-precompressed samples increases with an increase in the annealing temperature. However, when the precompressed samples are annealed at 300 ℃, their bending formability is lower than that of the extruded alloy because the dislocations formed by precompression remain even after the subsequent annealing at this temperature.

关键词： Magnesium Extrusion Bending Formability Texture

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Effects of 3D deformation and nonlinear stress–strain relationship on the Brazilian test for a transversely isotropic rock

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Journal of Rock Mechanics and Geotechnical Engineering 2023年第12期15卷 3221-3229页

作者： Juhyi Yim Yoonsung lee Seungki Hong ki-Bok Min R&D Center Hyundai Engineering and Construction75Yulgok-roJongno-guSeoulRepublic of Korea Department of Energy Systems Engineering and Research Institute of Energy and Resources Seoul National University1Gwanak-roGwanak-guSeoul08826Republic of Korea

To improve the accuracy of indirect tensile strength for a transversely isotropic rock in the Brazilian test, this study considered the three-dimensional (3D) deformation and the nonlinear stress–strain relationship. A parametric study of a numerical Brazilian test was performed for a general range of elastic constants, revealing that the 3D modeling evaluated the indirect tensile strength up to 40% higher than the plane stress modeling. For the actual Asan gneiss, the 3D model evaluated the indirect tensile strength up to 10% higher and slightly enhanced the accuracy of deformation estimation compared with the plane stress model. The nonlinearity in stress–strain curve of Asan gneiss under uniaxial compression was then considered, such that the evaluated indirect tensile strength was affected by up to 10% and its anisotropy agreed well with the physical intuition. The estimation of deformation was significantly enhanced. The further validation on the nonlinear model is expected as future research.

关键词： Anisotropy Transversely isotropy Brazilian test Indirect tensile strength Nonlinearity 3D modeling

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In?uence of Carbon Equivalent Value on the Weld Bead Bending Properties of High-Strength Low-Alloy Steel Plates

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Journal of Materials Science & Technology 2017年第4期33卷 321-329页

作者： ki hyuk kim In Jun Moon ki Won kim ki Bong Kang Byung Gyu Park Kwang Seok lee R&D Center of Dongkuk Steel Mill Co. Ltd Pohang 790-729 South Korea Korea Institute of Materials Science Implementation Research Division Materials Deformation Department 797 Changwondaero Changwon Gyeongnarn642-831 South Korea

The contribution of chemical compositions in terms of carbon equivalent value（CEV） on impending crack propagation during weld bead bend tests（WBBTs） was studied with five different high-strength lowalloy steel plates that underwent different rolling processes. The test showed that cracks developed at the weld joint, easily passed through the coarse-grain heat-affected zone（CGHAZ）, and finally were arrested within the heat-affected zone（HAZ）. An apparent decrease in the average crack length, which consequently indicated improvement in crack arrestability, was found with decreasing CEV. In addition,the relatively fine microstructure in the HAZ of low-CEV steel plates helped in preventing the crack from further propagation. Special emphasis was placed on the empirical expectation of critical CEV above which WBBT might fail.

关键词： Mechanical characterization Steel Welding Fracture Crack arrestability against bending

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Use of various MgO resources for high-purity Mg metal production through molten salt electrolysis and vacuum distillation

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Journal of Magnesium and Alloys 2023年第2期11卷 562-579页

作者： Hyeong-Jun Jeoung Tae-hyuk lee Youngjae kim Jin-Young lee Young Min kim Toru HOkabe Kyung-Woo Yi Jungshin Kang Korea Institute of Geoscience and Mineral Resources 124 Gwahak-ro Yuseong-guDaejeon 34132South Korea Department of Materials Science and Engineering Seoul National University1 Gwanak-roGwanak-guSeoul 08826South Korea Department of Resources Engineering University of Science and Technology217 Gajeong-ro Yuseong-guDaejeon 34113South Korea Korea Institute of Materials Science 797 Changwondae-roSeongsan-guChangwonGyeongnam 51508South Korea Institute of Industrial Science The University of Tokyo4-6-1 KomabaMeguro-kuTokyo 153-8505Japan School of Materials Science and Engineering Pusan National University2 Busandaehak-roGeumjeong-guBusan 44241South Korea

A green and effective electrolytic process was developed to produce high-purity Mg metal using primary and secondary resources containing Mg O as a feedstock. The electrolysis of various Mg O resources was conducted using a Cu cathode in MgF2– LiF – KCl molten salt at 1043 K by applying an average current of 1.44 A for 12.5 h. The electrolysis of calcined North Korean magnesite and seawater Mg O clinker yielded Mg alloys of MgCu2and(Cu) phases with current efficiencies of 89.6–92.4%. The electrolysis of oxidized Mg O-C refractory brick, aged ferronickel slag, and ferronickel slag yielded Mg alloys of MgCu2and(Cu) phases with current efficiencies of 59.3–92.3%. The vacuum distillation of Mg alloys obtained was conducted at 1300 K for 10 h to produce high-purity Mg metal. After vacuum distillation, Mg metal with a purity of above 99.994% was obtained. Therefore, this study demonstrates the feasibility of the production of high-purity Mg metal from various Mg O resources using a novel electrolytic process with a Cu cathode, followed by vacuum distillation.

关键词： High-purity magnesium Magnesium oxide resources Electrolytic process Metal cathode Vacuum distillation

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