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dynamic precipitation during multi-axial forging of an Mg-7Gd-5Y-1Nd-0.5Zr alloy

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Journal of Magnesium and Alloys 2013年第1期1卷 47-53页

作者： Ting Li Kui Zhang Xinggang Li Zhiwei Du Yongjun Li Minglong Ma Guoliang Shi State Key Laboratory for Fabrication and Processing of Non-ferrous Metals Beijing General Research Institute for Non-ferrous MetalsBeijing 100088China National Analysis and Testing Center for Nonferrous Metals&Electronic Materials Beijing General Research Institute for Non-ferrous MetalsBeijing 100088China

The dynamic precipitation behavior during multi-axial forging in an Mg-7Gd-5Y-1Nd-0.5Zr alloy has been investigated and compared with that in static precipitation treatment. The results indicated that dynamic precipitation does occur during multi-axial forging. The dynamic precipitate can be deduced as β phase with face-centered cubic crystal structure (a = 2.22 nm). Most of the β precipitates locate at the dynamic recrystallization grain boundaries. The morphology and orientation relationship is different from that of the β phase formed in the static precipitation treated alloys, although the crystal structure is the same. The precipitation temperature of β phase during MAF is higher than that in the static precipitation treatment.

关键词： Magnesium alloy Multi-axial forging dynamic precipitation

dynamic Recrystallization and precipitation Behavior of Mn-Cu-V Weathering Steel

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Journal of Materials Science & Technology 2011年第12期27卷 1131-1138页

作者： Hongyan Wu Linxiu Du Xianghua Liu State Key Laboratory of Rolling and Automation Northeastern University Shenyang 110819 China

The hot deformation behavior of a Mn-Cu-V weathering steel was investigated at temperatures ranging from 850 to 1050℃ and strain rates ranging from 0.01 to 5 s-1 using MMS-300 thermal-mechanical simulator. The activation energy for dynamic recrystallization and stress exponent were calculated to be 551 kJ/mol and 7.73, respectively. The accurate values of critical strain were determined by the relationship between work hardening rate and flow stress （θ-σ） curves. The hyperbolic sine constitutive equation was employed to describe the relationship between the peak stress and Zener-Hollomon parameter during hot deformation. The interaction between dynamic recrystallization and dynamic precipitation of V（C,N） at a low strain rate was analyzed. The results showed that precipitation particles size of weathering steel increased with increasing strain at deformation temperature g50~C and strain rate 0.1 s-I. The calculation results of the recrystallization driving force and pinning force showed that dynamic precipitation could retard the progress of dynamic recrystallization but not prevent it while the pinning forces is less than driving force. On the contrary, dynamic precipitation can effectively prevent the progress of dynamic recrystallization.

关键词： Weathering steel Critical strain dynamic recrystallization dynamic precipitation

Composition-dependent dynamic precipitation and grain refinement in Al-Si system under high-pressure torsion

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Journal of Materials Science & Technology 2021年第9期68卷 199-208页

作者： Shenbao Jin Zhenjiao Luo Xianghai An Xiaozhou Liao Jiehua Li Gang Sha Herbert Gleiter Institute of Nanoscience School of Materials Science and EngineeringNanjing University of Science and TechnologyNanjing210094 China School of Aerospace Mechanical and Mechatronic EngineeringThe University of SydneyNSW2006Australia Institute of Casting Research Montanuniversitat LeobenA-8700LeobenAustria

Understanding composition effects is crucial for alloy design and development. To date, there is a lack of research comprehensively addressing the effect of alloy composition on dynamic precipitation, segregation and grain refinement under severe-plastic-deformation processing. This research investigates Al-x Si alloys with x = 0.1, 0.5 and 1.0 at.% Si processed by high pressure torsion(HPT) at room temperature by using transmission electron microscopy, transmission Kikuchi diffraction and atom probe tomography. The alloys exhibit interesting composition-dependent grain refinement and fast dynamic decomposition under HPT processing. Si atoms segregate at dislocations and Si precipitates form at grain boundaries(GBs) depending on the Si content of the alloys. The growth of Si precipitates consumes most Si atoms segregating at GBs, hence the size and distribution of the Si precipitates become predominant factors in controlling the grain size of the decomposed Al-Si alloys after HPT processing. The hardness of the Al-Si alloys is well correlated with a combination of grain-refinement strengthening and the decomposition-induced softening.

关键词： Al-Si alloys Composition effects dynamic precipitation Solute segregation Grain refinement

Effects of dynamic recrystallization and strain-induced dynamic precipitation on the corrosion behavior of partially recrystallized Mg-9Al-lZn alloys

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Journal of Magnesium and Alloys 2020年第4期8卷 1016-1037页

作者： Yenny Cubides Dexin Zhao Lucas Nash Digvijay Yadav Kelvin Xie Ibrahim Karaman Homero Castaneda Department of Materials Science and Engineering Texas A&M University575 Ross StreetCollege StationTX 77840USA Department of Engineering Technology and Industrial Distribution 106 Ross StreetCollege StationTX 77843USA National Corrosion and Materials Reliability Laboratory 1041 RELLIS PkwyBryanTX 77807USA

The corrosion susceptibility of recrystallized and un-recrystallized grains in equal channel angular pressed(ECAPed)Mg-9Al-lZn(AZ91)alloys immersed in chloride containing media was investigated through immersion testing and an electrochemical microcell technique coupledwith high resolution techniques such as scanning Kelvin probe force microscopy(SKPFM),transmission electron microscopy(TEM),andelectron backscatter diffraction(EBSD).During ECAP,dynamic recrystallization(DRX)and strain-induced dynamic precipitation(SIDP)simultaneously occurred,resulting in a bimodal grain structure of original elongated coarse grains and newly formed equiaxed fine grainswith a large volume fraction ofβ-Mg17Al12 precipitates.Corrosion preferentially initiates and propagates in the DRXed grains,owing tothe greater microchemistry difference between theβ-Mg17Al12 precipitates formed at the DRXed grain boundaries and the adjacentα-Mgmatrix,which induces a strong microgalvanic coupling between these phases.Additionally,the weaker basal texture of the DRXed grainsalso makes these grains more susceptible to electrochemical reactions than the highly textured un-DRXed grains.The influence of dynamicrecrystallization and dynamic precipitation was also studied in ECAPed alloys with differenl levels of deformation strain through corrosion andelectrochemical techniques.Increasing the strain level led to a more uniform corrosion with a shallow penetration depth,lower corrosion ratevalues,and higher protective ability of the oxide film.Furthermore,higher levels of strain resulted in greater hardness values of the ECAPedalloys.The superior corrosion resistance and strength of the ECAPed alloys with increasing strain level was attributed to the combination ofsmaller DRXed grain size,higher DRX ratio,and higher volume fraction of uniformly distributed fineβ-Mg17Al12 precipitates.c 2020 Published by Elsevier B.V.on behalf of Chongqing University.

关键词： Magnesium alloy Bimodal grain structure dynamic recrystallization dynamic precipitation Severe plastic deformation Microgalvanic coupling

Effects of minor Nd and Er additions on the precipitation evolution and dynamic recrystallization behavior of Mg-6.0Zn-0.5Mn alloy

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Journal of Magnesium and Alloys 2021年第3期9卷 840-852页

作者： Bin-Jiang Lv Sen Wang Tie-Wei Xu Feng Guo School of Mechanical and Automotive Engineering Qingdao University of Technology266520China Key Lab of industrial Fluid Energy Conservation and Pollution Control Qingdao University of Technology266520China

A new wrought magnesium(Mg)alloy based on Mg-6.0Zn-0.5Mn(ZM60)is developed,which performs excellent combination of high tensile yield strength and good ductility.We investigate the effects of micro-alloying on dynamic precipitation,dynamic recrystallization(DRX)and mechanical properties of ZM60 alloy.The co-addition of minor(0.6 wt%)neodymium(Nd)and(0.3 wt%)erbium(Er)can accelerate the twinning and DRX process of ZM60 alloy at the initial compression deformation stage.The dynamic precipitation process is also accelerated due to Nd and Er co-alloying.Dislocation accumulation disappears and a higher density of rodβ_(1) precipitates and some thick β_(2) precipitates in matrix and fine twins,which inhibits the growth of DRX grains in compressed ZM60-0.6Nd-0.3Er alloy.The as-extruded ZM60-0.6Nd-0.3Er alloy has a yield strength(YS)of 245.8 MPa,ultimate tensile strength(UTS)of 347.2 MPa and elongation(EL)of 16.3%.The yield strength and tensile strength are improved via minor Nd and Er additions due to fine complete DRX grains,second phase particles and high density of precipitates.The grain refinement,weakened reserved working hardening and weakened basal fiber texture improve the elongation of ZM60-0.6Nd-0.3Er alloy.

关键词： Nd and Er Hot deformation dynamic precipitation dynamic recrystallization Texture

dynamic precipitation Behaviors and Mechanical Properties of Mg-12Gd-3Y-0.5Zr Alloy Processed by Secondary Extrusion

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Dynamic Precipitation Behaviors and Mechanical Properties of...

Effect of heat treatment on the microstructure and mechanical properties of a multidirectionally forged Mg-Gd-Y-Zn-Zr-Ag alloy

中国材料大会2012

作者： Dejiang Li Yinpeng Zhou Xiaoqin Zeng Wenjiang Ding Bin Chen Yingzheng Liu National Engineering Research Centre of Light Alloy Net Forming the State Key Laboratory of Metal Matrix CompositesShanghai Jiaotong University Instrumental Analysis Center of School of Materials Science and Engineering Shanghai Jiaotong University School of Mechanical Engineering Shanghai Jiao Tong University

ISBN: (纸本)9783037856086;3037856084

Secondary extrusion at 350 ℃ with the extrusion ratio of 12.25, 25 and 44 was carried out on the Mg-12Gd-3Y-0.5Zr （GW123K） alloy, and the cooling method of the secondary extruded alloys was air cooling and water quenching. Quantitative metallographic analysis method was also employed to study the distribution and volume fraction of dynamic precipitates during the extrusion process. The results showed that secondary extrusion could result in significant grain refinement and the grain size increased with extrusion ratio, which the minimum average grain size was about 5.4μm in the alloy under λ=12.25. The volume fraction of dynamic precipitates decreased with increasing extrusion ratio and the maximum volume fraction was measured to be about 49.2% in the alloy under λ =12.25. Water quenching after extrusion can effectively inhibit dynamic precipitation and the volume fraction of the precipitates ratio decreased from 41.1% after air cooling to 19.6% after water quenching in the same extrusion condition. Tensile properties results showed that the age hardening response of the alloys was decreased by dynamic precipitation and water quenching was an efficient method which is able to avoid this behavior in some extent.

关键词： Mg-Gd-Y-Zr alloys Secondary extrusion dynamic precipitation precipitation hardening Mechanical properties

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镁合金学报(英文) 2023年第6期11卷 2042-2053页

作者： Junkai Wang Chuming Liu Shunong Jiang Yingchun Wan Zhiyong Chen School of Materials Science and Engineering Central South UniversityChangsha 410083China State Key Laboratory for Powder Metallurgy Central South UniversityChangsha 410083China School of Materials Science and Engineering Hunan University of Science and TechnologyXiangtan 411201China

Multidirectional forging(MDF)was successfully applied to fabricate large-size Mg-Gd-Y-Zn-Zr-Ag alloy in this work and effects of T4,T5 and T6 treatments on the microstructure and mechanical properties of the as-forged alloy were analyzed.Results show that dynamic recrystallization(DRX)occurs and second phase particles precipitate along the grain boundary during the MDF process.After annealing treatment(T4),the volume fraction and size of dynamic precipitates slightly increase at a lower temperature(430℃)compared with those of MDFed sample,while they are dissolved into theα-Mg matrix at a higher temperature(450℃).At the meantime,short plate-shaped long-period stacking ordered(LPSO)phases are observed in the DRX grains of the MDFed sample and then dissolved into theα-Mg matrix during annealing at both temperatures.Typical basal texture is identified in the MDFed sample,but the basal pole tilts away from final forging direction and rare-earth texture component withorientation parallel to penultimate forging direction becomes visible after annealing.The T6 sample annealing at 430℃for 4 h and ageing at 200℃for 34 h exhibits the superior strength and ductility in this study.The ultimate tensile strength,tensile yield strength and elongation to failure,which is 455 MPa,308 MPa and 7.7%,respectively,are overall improved compared with the directly-aged(T5)sample.This paper provides a superior heat treatment schedule to manufacture high-performance large-scale Mg-Gd-Y-Zn-Zr-Ag components for industrial production.

关键词： Mg-Gd-Y-Zn-Zr-Ag alloy Multidirectional forging dynamic precipitation Heat treatment Mechanical properties

Bimodal grain structure formation and strengthening mechanisms in Mg-Mn-Al-Ca extrusion alloys

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Journal of Magnesium and Alloys 2023年第12期11卷 4407-4419页

作者： Jianyue Zhang Peng Peng Qingshan Yang Alan A.Luo Department of Materials Science and Engineering The Ohio State UniversityColumbusOH 43210USA School of Metallurgy and Material Engineering Chongqing University of Science and TechnologyChongqing401331China Department of Integrated Systems Engineering The Ohio State UniversityColumbusOhio 43210USA

The effects of small additions of calcium (0.1%and 0.5%~1) on the dynamic recrystallization behavior and mechanical properties of asextruded Mg-1Mn-0.5Al alloys were investigated.Calcium microalloying led to the formation of Al_(2)Ca in as-cast Mg-1Mn-0.5Al-0.1Ca alloy and both Mg_(2)Ca and Al_(2)Ca phases in Mg-1Mn-0.5Al-0.5Ca alloy.The formed Al_(2)Ca particles were fractured during extrusion process and distributed at grain boundary along extrusion direction (ED).The Mg_(2)Ca phase was dynamically precipitated during extrusion process,hindering dislocation movement and reducing dislocation accumulation in low angle grain boundaries (LAGBs) and hindering the transformation of high density of LAGBs into high angle grain boundaries (HAGBs).Therefore,a bimodal structure composed of fine dynamically recrystallized (DRXed) grains and coarse un DRXed regions was formed in Ca-microalloyed Mg-1Mn-0.5Al alloys.The bimodal structure resulted in effective hetero-deformation-induced (HDI) strengthening.Additionally,the fine grains in DRXed regions and the coarse grains in un DRXed regions and the dynamically precipitated Mg_(2)Ca phase significantly enhanced the tensile yield strength from 224 MPa in Mg-1Mn-0.5Al to335 MPa and 352 MPa in Mg-1Mn-0.5Al-0.1Ca and Mg-1Mn-0.5Al-0.5Ca,respectively.Finally,a yield point phenomenon was observed in as-extruded Mg-1Mn-0.5Al-x Ca alloys,more profound with 0.5%Ca addition,which was due to the formation of (■) extension twins in un DRXed regions.

关键词： Magnesium alloys Extrusion dynamic precipitation dynamic recrystallization Bimodal grain structure Mechanical properties

Hot compressive deformation behaviors of Mg–10Gd–3Y–0.5Zr alloy

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Progress in Natural Science:Materials International 2016年第1期26卷 78-84页

作者： Tingting Zheng Dejiang Li Xiaoqin Zeng Wenjiang Ding National Engineering Research Center of Light Alloy Net Forming School of Materials Science and Engineering Shanghai Jiao Tong University

In this paper, the hot compressive deformation characteristics of a Mg–10Gd–3Y–0.5Zr（GW103K） alloy have been investigated by isothermal compression test at the temperature range of 350–450°C and strain rate range of 0.0001–0.1s;. True stress–strain relationships at various strain rates showed the typical strain hardening and softening stage which is indicative of dynamic recrystallization during deformation. The results showed that the peak stress was obviously dependent on temperature and strain rate. A constitutive equation to describe the deformation process was established based on the hyperbolic sine function. The stress exponent n and apparent activation energy Q were determined to be 3.018 and 203.947 k J/mol, respectively. Microstructure investigation showed that dislocation slipping was the dominant deformation mechanism during the hot deformation at all conditions. However, at the temperatures lower than 400 °C and strain rates higher than 0.01 s;, twinning was observed to be activated, which indicated another deformation mechanism. dynamic recrystallization and dynamic precipitation were found to occur simultaneously under such deformation condition.

关键词： Mg-RE alloys Hot deformation dynamic precipitation Constitutive equation Microstructure evolution