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Superplastic behavior of a fine-grained Mg-Gd-Y-Ag alloy processed by equal channel angular pressing

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Journal of Magnesium and Alloys 2023年第10期11卷 3815-3828页

作者： A.rezaei r.mahmudi r.E.Logé School of Metallurgical and Materials Engineering College of EngineeringUniversity of TehranTehran 14395-515Iran Laboratory of Thermomechanical Metallurgy-PX Group Chair Ecole Polytechnique Fédérale de Lausanne(EPFL)CH-2002 NeuchâtelSwitzerland

An extruded Mg-6Gd-3Y-1.5Ag(wt%) alloy was processed by 6 passes of equal channel angular pressing(ECAP) at 553 K using route Bc to refine the microstructure. Electron back-scattered diffraction(EBSD) analysis showed a fully recrystallized microstructure for the extruded alloy with a mean grain size of 8.6 μm. The microstructure of the ECAP-processed alloy was uniformly refined through dynamic recrystallization(DrX). This microstructure contained fine grains with an average size of 1.3 μm, a high fraction of high angle grain boundaries(HAGBs), and nano-sized Mg_(5)Gd-type particles at the boundaries of the DrXed grains, detected by transmission electron microscopy(TEM). High-temperature shear punch testing(SPT) was used to evaluate the superplastic behavior of both the extruded and ECAP-processed alloys by measuring the strain rate sensitivity(SrS) index(m-value). While the highest m-value for the extruded alloy was measured to be 0.24 at 673 K, the ECAP-processed alloy exhibited much higher m-values of 0.41 and 0.52 at 598 and 623 K, respectively,delineating the occurrence of superplastic flow. Based on the calculated average activation energy of 118 kJ mol^(-1) and m-values close to 0.5, the deformation mechanism for superplastic flow at the temperatures of 598 and 623 K for the ECAP-processed alloys was recognized to be grain boundary sliding(GBS) assisted by grain boundary diffusion.

关键词： Mg-Gd-Y alloys Equal channel angular pressing Superplasticity Strain rate sensitivity Grain boundary sliding

Simple shear extrusion versus equal channel angular pressing:A comparative study on the microstructure and mechanical properties of an Mg alloy

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Journal of Magnesium and Alloys 2023年第5期11卷 1769-1790页

作者： A.rezaei r.mahmudi C.Cayron r.E.Logé School of Metallurgical and Materials Engineering College of EngineeringUniversity of TehranNorth Kargar StreetTehran 14395-515Iran Laboratory of Thermomechanical Metallurgy-PX Group Chair Ecole Polytechnique Fédérale de Lausanne(EPFL)Neuchâtel CH-2002Switzerland

Two severe plastic deformation(SPD)techniques of simple shear extrusion(SSE)and equal channel angular pressing(ECAP)were employed to process an extruded Mg-6Gd-3Y-1.5Ag(wt%)alloy at 553 K for 1,2,4 and 6 *** microstructural evolutions were studied by electron back scattered diffraction(EBSD)analysis and transmission electron microscopy(TEM).The initial grain size of 7.5μm in the extruded alloy was reduced to about 1.3μm after 6 SPD *** dynamic recrystallization was suggested to be operative in both SSE and ECAP,with also a potential contribution of continuous dynamic recrystallization at the early stages of *** difference in the shear strain paths of the two SPD techniques caused different progression rate of dynamic recrystallization(DrX),so that the alloys processed by ECAP exhibited higher fractions of recrystallization and high angle grain boundaries(HAGBs).It was revealed that crystallographic texture was also significantly influenced by the difference in the strain paths of the two SPD methods,where dissimilar basal plane texture components were *** compression tests,performed along extrusion direction(ED),indicated that the compressive yield stress(CYS)and ultimate compressive strength(UCS)of the alloys after both SEE and ECAP augmented continuously by increasing the number of ***-processed alloys had lower values of CYS and UCS compared to their counterparts processed by *** difference in the mechanical responses was attributed to the different configurations of basal planes with respect to the loading direction(ED)of each SPD technique.

关键词： Mg-Gd-Y alloys Severe plastic deformation Simple shear extrusion Equal channel angular pressing Dynamic recrystallization Mechanical properties

Effect of texture and twinning on mechanical properties and corrosion behavior of an extruded biodegradable Mg-4Zn alloy

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Journal of Magnesium and Alloys 2019年第4期7卷 707-716页

作者： M.Sabbaghian r.mahmudi K.S.Shin School of Metallurgical and Materials Engineering College of EngineeringUniversity of TehranTehran 14395-515Iran Magnesium Technology Innovation Center School of Materials Science and EngineeringSeoul National University1 Gwanak-roGwanak-guSeoul 08826Republic of Kore

Microstructure,texture,mechanical properties and corrosion behavior of the extruded Mg-4Zn alloy,as a biodegradable material,were investigated.A refined microstructure caused by dynamic recrystallization(DrX),and a general fiber texture were achieved after *** properties along different directions of the extruded samples were investigated using shear punch test(SPT).The shear yield stress(SYS)of 113.8 MPa obtained in the transverse direction(TD)was higher than the 106 MPa achieved for the extruded direction(ED)and 45˚*** was attributed to the higher amounts of twins and also lower Schmid factor(SF)in the *** the other hand,encouraged activation of the basal slip system in the 45˚samples resulted in improved room temperature formability,as indicated by the normalized displacement in the SPT *** back scattered diffraction(EBSD)analysis of the surfaces corroded in the phosphate buffered saline(PBS)solution,showed that despite having similar grain sizes and second phase particles shape and volume fractions,surfaces containing grains near(0001)orientations and extension twins(TD and 45˚samples)have lower corrosion rates,as compared to the ED specimens.

关键词： Mg-Zn alloy Corrosion rate Dynamic recrystallization Texture Twinning

Significant improvements in mechanical properties of AA5083 aluminum alloy using dual equal channel lateral extrusion

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Transactions of Nonferrous Metals Society of China 2016年第12期26卷 3081-3090页

作者： N.FAKHAr F.FErESHTEH-SANIEE r.mahmudi Department of Mechanical Engineering Faculty of EngineeringBu-Ali Sina University School of Metallurgical and Materials Engineering College of EngineeringUniversity of Tehran

Dual equal channel lateral extrusion (DECLE), as a severe plastic deformation (SPD) process, was employed forimproving the mechanical properties of AA5083 aluminum alloy. Several experiments were conducted to study the influences of theroute type, namely A and B, and pass number on mechanical properties of the material. The process was conducted up to 6 passeswith decreasing process temperature, specifically from 573 to 473 K. Supplementary experiments involving metallography, hardnessand tensile tests were carried out in order to evaluate the effects of the process variables. The hardness measurements exhibitedreasonably uniform distributions within the product with a maximum increase of 64% via a 6-pass operation. The yield and ultimatestrengths also amended 107% and 46%, respectively. These significant improvements were attributed to the severe shear deformationof grains and decreasing pass temperature, which intensified the grain refinement. TEM images showed an average grain sizereduction from 100 μm for the annealed billet to 200 nm after 6 passes of DECLE. Finally, the experimental findings for routes A andB were compared and discussed and some important conclusions were drawn.

关键词： AA5083 aluminum alloy severe plastic deformation dual equal channel lateral extrusion hardness homogeneity

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细晶粒铝合金板材的机械性能和成形性能

轻合金加工技术 1988年第12期 13-18页

作者： r.mahmudi 黄庆汉

以Al—Fe—Si、Al—Fe—Mn或Al—Ni—(Fe、Mn)为基的铝合金,经过铸锭轧制和适当的加工处理使其具有细小而规则的弥散金属间化合物时,能够提供很细小的晶粒组织,并且在板材延伸时有极好的强度和塑性配合。本文介绍含Fe1.4％、Mn0.4％的... 详细信息

以Al—Fe—Si、Al—Fe—Mn或Al—Ni—(Fe、Mn)为基的铝合金,经过铸锭轧制和适当的加工处理使其具有细小而规则的弥散金属间化合物时,能够提供很细小的晶粒组织,并且在板材延伸时有极好的强度和塑性配合。本文介绍含Fe1.4％、Mn0.4％的、用直接水冷铸造的AA8014 Al—Fe—Mn合金铸锭生产的板材的成形性能。

关键词：成形性能铝合金板材细晶粒应变硬化工业纯铝应变速率成形极限晶粒尺寸流变应力硬化速率

The role of geometrical features in the architecturalstructural interaction:Some case studies of the Iranian ancient architecture

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Frontiers of Structural and Civil Engineering 2019年第3期13卷 716-724页

作者： Maryam ZANDIYEHVAKILI Isa HOJAT Mehdi mahmudi Faculty of Architecture and Urban Development Art University of IsfahanIsfahanIran Faculty of Architecture College of Fine ArtsUniversity of TehranTehranIran

This research aims to enhance the interaction between a structure and its architectural *** a qualitative approach,the present work discovers some successfully used geometrical features of the Iranian ancient architecture in terms of the architectural-structural *** define four qualitative criteria for this assessment,i.e.,construction-ability,cost effectiveness,participation of the structure in fulfillment of the visual,and functional-semantic needs of the architectural *** this purpose,two case studies including the Jame Mosque of Isfahan and the Soltaniyeh building are *** outcomes of this research help designers to not only design efficient structures by adapting non-load bearing elements with the general form of the structure,but also meet concepts such as the unity or perfectionism in the structure.

关键词： architectural-structural interaction geometrical features structure architectural form Iranian ancient architecture

Prediction of Earing in Deep Drawing of roll-cast Aluminium Alloy Sheets

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厦门大学学报（自然科学版） 2002年第S1期41卷 99-101页

作者： r.mahmudi M Aghaie-Khafri Department of Metallurgy and Materials Engineering Faculty of Engineering University of TehranDepartment of Metallurgy and Materials Engineering Faculty of Engineering University of Tehran Tehran IranTehran Iran

Commercial aluminium alloy sheets are presently sem ic ontinuously, direct chill casting billets that are hot and cold rolled to the fi nal gauge. Interest has been shown in continuous methods which eliminate the ho t rolling step through rapid solidification of the molten metal to the final sla b. Accordingly, sheets are produced by homogenization, cold rolling, intermedia te and final annealing of these roll-cast slabs. The problem of earing is of gr eat concern as it causes frequent interruption of production runs and leads to m aterial wastage. Therefore, it is quite desirable that earing can be predic ted and consequently necessary measures be taken to minimize or eliminate this u nwanted phenomenon. It is accepted generally that, the principal source of earing is the crystallogr aphic anisotropy arising from non-random distribution of crystal orientations i n the material. Accordingly, several attempts have been made to correlate the m echanical and crystallographic properties of the materials to the earing behavio ur for predictive purposes. Some of these are based on continuum concepts which concentrate on the macroscopic rather than the microscopic aspects of the mater ials. To accommodate the microstructural features of the material, some models have been developed. A more recent approach which provides a connection between texture and plastic anisotropy parameters of the material is the Continuum Mech anics of Textured Polycrystals (CMTP) method proposed by Lin et al. A simplifie d version of this method has been suggested by Chan with promising accuracy for aluminium and copper sheets. AA3105 and AA8011 aluminium alloy sheets were used in this investigation. The a s-cast slabs were cold rolled to the final thickness of 1.0 mm. Different anne aling temperatures in the range of 420 ℃ to 540 ℃ produced a range of r-value s. Circular blanks of 60 mm diameter were machined and deep drawn using a cylind rical flat-bottom punch of 33 mm diameter. The heights of

关键词： Prediction of Earing in Deep Drawing of roll-cast Aluminium Alloy Sheets

Effects of cold rolling on the microstructure and mechanical properties of Fe-Ni-Mn-Mo-Ti-Cr maraging steels

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International Journal of Minerals,Metallurgy and Materials 2011年第5期18卷 557-561页

作者： Abbas mahmudi Syamak Hossein Nedjad Mir Masud Jabbari Behnam Young researchers Club Islamic Azad University (Ahar Branch)54516 AharTabrizIran Faculty of Materials Engineering Sahand University of TechnologyTabriz 51335-1996Iran Department of Materials Science and Engineering Sharif University of TechnologyTehran 11365Iran

Effects of cold rolling on the microstructure and mechanical properties of Fe-Ni-Mn-Mo-Ti-Cr maraging steels were *** investigate the microstructure and mechanical properties,optical microscopy,scanning electron microscopy,X-ray diffraction,tensile test,and hardness test were *** results show that the solution-annealing treatment in the cold-rolled steel redounds to the formation of sub-microcrystalline Fe2（Mo,Ti） Laves phase particles,which are stable at high *** secondary Laves phase particles prevent from recrystallization at high temperatures and correspond to semi-brittle fracture in the subsequent aging treatment.

关键词： maraging steel cold rolling age hardening Laves-phase microstructure mechanical properties

Temperature-jump tensile tests to induce optimized TrIP/TWIP effect in a metastable austenitic stainless steel

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International Journal of Minerals,Metallurgy and Materials 2024年第9期31卷 2025-2036页

作者： Mohammad Javad Sohrabi Hamed Mirzadeh Saeed Sadeghpour Abdol reza Geranmayeh reza mahmudi School of Metallurgy and Materials Engineering College of EngineeringUniversity of Tehran14395-515TehranIran Centre for Advanced Steels research Materials and Mechanical EngineeringUniversity of Oulu90014 OuluFinland

In the present work,plastic deformation mechanisms were initially tailored by adjusting the deformation temperature in the range of 0 to 200℃ in AISI 304L austenitic stainless steel,aiming to optimize the strength-ductility *** was shown that the combined twinning-induced plasticity(TWIP)/transformation-induced plasticity(TrIP)effects and a wider strain range for the TrIP effect up to higher strains by adjusting the deformation temperature are good strategies to improve the strength-ductility synergy of this metastable stainless *** this regard,by consideration of the observed temperature-dependency of plastic deformation,the controlled sequence of TWIP and TrIP effects for archiving superior strength-ductility trade-off was intended by the pre-designed temperature jump tensile ***,the optimum tensile toughness of 846 MJ/m^(3) and total elongation to 133% were obtained by this strategy via exploiting the advantages of the TWIP effect at 100℃ and the TrIP effect at 25℃ at the later stages of the ***,a deformation-temperature-transformation(DTT)diagram was developed for this metastable ***,based on work-hardening analysis,it was found that the main phenomenon constraining further improvement in the ductility and strengthening was the yielding of the deformation-induced α′-martensite.

关键词： metastable stainless steels transformation-induced plasticity twinning-induced plasticity stacking fault energy mechanical properties