Mechanical properties and microstructure evolution in ultrafine-grained AZ31 alloy processed by severe plastic deformation

Vrátná, Jitka; Janeček, Miloš; Čı́žek, Jakub; Lee, Dong Jun; Yoon, Eun Yoo; Kim, Hyoung Seop

doi:10.1007/s10853-013-7151-x

Cited by 27 publications

(8 citation statements)

References 35 publications

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“…There is a reasonable level of hardness homogeneity which is achieved across the HPT disks through ten turns with a saturation hardness value of Hv ≈ 125 as shown in Figure 2 [6]. This gradual development of hardness homogeneity is consistent with several experimental reports for magnesium alloys processed by HPT [7][8][9][10]. There are many other papers reporting the enhanced strength of UFG materials processed by SPD methods [11][12][13][14][15].…”

Section: Multifunctional Properties Of Ultrafine-grained Materials 2supporting

confidence: 85%

Innovative Applications of Ultrafine-Grained Materials

Xu¹,

Guo²,

Shan³

2017

Severe Plastic Deformation Techniques

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This chapter focuses on multifunctional properties of ultrafine-grained (UFG) metallic materials processed by severe plastic deformation (SPD), such as enhanced mechanical properties, excellent superplasticity, and wear resistance. Based on these multifunctional properties, the potential innovative application for UFG materials processed by SPD is introduced in the next section, including innovative application in micro-forming, nanoimplants, electro-connections, and sport engineering.

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Section: Multifunctional Properties Of Ultrafine-grained Materials 2supporting

confidence: 85%

Innovative Applications of Ultrafine-Grained Materials

Xu¹,

Guo²,

Shan³

2017

Severe Plastic Deformation Techniques

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“…It has been reported that in HPT-processed AZ31 and AZ91 alloys the dislocation density, as measured by positron lifetime spectrometry and XRD, increased gradually to about ~1.2×10 14 m -2 and ~2×10 14 m -2 , respectively, after processing for the first several turns [35,36], whilst the model in [37] predicts a dislocation density of 1.4× 10 14 m -2 for pure Mg processed by HPT to a saturated hardness. In the present alloy, the dislocation density increases dramatically at the early stage, and after 10 and 16 turns, the saturated dislocation density reaches ~3.2×10 14 m -2 .…”

Section: Discussionmentioning

confidence: 99%

Evolution of microstructure and mechanical properties of an as-cast Mg-8.2Gd-3.8Y-1.0Zn-0.4Zr alloy processed by high pressure torsion

Sun

Qiao

et al. 2017

Materials Science and Engineering: A

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Abstract:The novel Mg-8.2Gd-3.8Y-1.0Zn-0.4Zr alloy with high content of rare earth elements has been processed successfully by high pressure torsion (HPT) starting from an as-cast condition. HPT processing was conducted at room temperature for a range of turns from 1/8 to 16, and the evolutions of microstructure and microhardness were investigated.The average grain size decreases from ~85 μm in the as-cast condition to ~55 nm when the equivalent strain reaches ~6.0, and remains almost constant on further strain increase. Meanwhile, the coarse netlike Mg3(Gd,Y) second phase structures are gradually broken into fine dispersed particles and the dislocation density increases. The microhardness of the alloy increases with increasing strain, and when the equivalent strain reaches ~6.0, the microhardness reaches a saturated value of about 115 HV, which is higher than that obtained by conventional extrusion / rolling of this alloy. The full range of possible mechanisms of hardening are analysed and this reveals that hardening is primarily due to the pronounced grain refinement, which is substantially 2 stronger than that for HPT-processed conventional Mg alloys, and to the homogeneously distributed fine second phase particles and the high dislocation density.

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“…However, the creep behaviour is also enhanced by fast diffusion paths like pipe diffusion along dislocations or grain boundaries, which might be dominant diffusion processes due to highly deformed UFG microstructure [14,15]. Note also that activation energy of grain boundary diffusion in pure Mg (92 kJ/mol [16]) is much lower than the activation energy of self-diffusion (135 kJ/mol [16]).…”

Section: Discussionmentioning

confidence: 99%

Continuous measurement of m-parameter for Hart analysis of superplastic behaviour of ultra-fine grained AZ31 Mg alloy

Stráský¹,

Stráská²

2015

LoM

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The ultra-fine grained materials (UFG) often show superplastic behaviour at elevated temperatures due to small grain size. On the other hand, UFG microstructure is often not stable at increased temperatures and undergoes recovery and recrystallization. In this paper, we investigate the superplastic properties of UFG AZ31 Mg alloy prepared by equal channel angular pressing. The computer controlled tensile tests were performed in a temperature range of 175°C−250°C and at strain rate around 10 -4 s -1 . The superplastic behaviour and strain hardening is related to temperature, strain-rate and microstructure stability. Methodology of continuous measurement of m-parameter during the tensile test to achieve the dependence of m-parameter on true strain is presented. The measurement is based on alternating two slightly different true strain rates, keeping the overall true strain-rate constant. The m-parameter decreases with true strain for all studied conditions from approx. 0.5 to 0.3 and the decrease is fastest for the highest considered temperature (250°C), which is attributed to recovery and recrystallization. The sample deformed at 250°C strain hardens over significantly shorter interval of true strain which also suggests microstructure changes. Limits of plastic instability according to Hart analysis were computed for all conditions. Hart analysis of stability of plastic deformation seems not to be sufficient for description of elongation until fracture for studied material.Keywords: superplastic behaviour, plastic instability, m-parameter, ultra-fine grained, magnesium alloy Непрерывное измерение параметра m для анализа Харта сверхпластического поведения ультрамелкозернистого магниевого сплава AZ31Ультрамелкозернистые (УМЗ) материалы часто демонстрируют сверхпластическое поведение при повышенных тем-пературах благодаря малому размеру зерен. С другой стороны, УМЗ микроструктура часто нестабильна при высо-ких температурах и испытывает возврат и рекристаллизацию. В данной работе мы исследуем сверхпластические свойства УМЗ магниевого сплава AZ31, подвергнутого равноканальному угловому прессованию. Были проведены управляемые компьютером испытания в температурном интервале 175°C-250°C при скорости деформации около 10 -4 с -1. Сверхпластическое поведение и упрочнение связаны с температурой, скоростью деформации и стабильно-стью микроструктуры. Представлена методология непрерывного измерения параметра m во время испытаний рас-тяжением для получения зависимости параметра m от истинной деформации. Измерение основано на чередовании двух незначительно различающихся скоростей деформации при сохранении средней истинной скорости деформа-ции постоянной. Параметр m для всех исследованных случаев уменьшается с увеличением истинной деформации приблизительно от 0.5 до 0.3, и уменьшение наиболее интенсивно для наиболее высокой исследованной темпера-туры (250°C), что связано с возвратом и рекристаллизацией. Образец, деформируемый при 250°C, упрочняется за значительно более короткий интервал истинной деформации, что также говорит об из...

show abstract

Mechanical properties and microstructure evolution in ultrafine-grained AZ31 alloy processed by severe plastic deformation

Cited by 27 publications

References 35 publications

Innovative Applications of Ultrafine-Grained Materials

Innovative Applications of Ultrafine-Grained Materials

Evolution of microstructure and mechanical properties of an as-cast Mg-8.2Gd-3.8Y-1.0Zn-0.4Zr alloy processed by high pressure torsion

Continuous measurement of m-parameter for Hart analysis of superplastic behaviour of ultra-fine grained AZ31 Mg alloy

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