Ductility enhancement in AZ31 magnesium alloy by controlling its grain structure

Mukai, Toshiji; Yamanoi, Masashi; Watanabe, Hiroyuki; Higashi, Kenji

doi:10.1016/s1359-6462(01)00996-4

Cited by 767 publications

(362 citation statements)

References 9 publications

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“…Second, because of variations in atomic arrangement, grain boundaries can act as preferred sources for the nucleation and emission of dislocations (30,31). It has been reported that Mg alloys processed by equal channel angular processing or hot rolling for grain refinement exhibit not only higher yield stresses but larger elongations at room temperature (32)(33)(34). However, conflicting results have also been reported mainly due to the texture characteristics and complication of deformation twinning (35,36).…”

Section: Discussionmentioning

confidence: 99%

Reducing deformation anisotropy to achieve ultrahigh strength and ductility in Mg at the nanoscale

Qi²,

Mishra

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

115

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In mechanical deformation of crystalline materials, the critical resolved shear stress (CRSS; τ CRSS ) is the stress required to initiate movement of dislocations on a specific plane. In plastically anisotropic materials, such as Mg, τ CRSS for different slip systems differs greatly, leading to relatively poor ductility and formability. However, τ CRSS for all slip systems increases as the physical dimension of the sample decreases to approach eventually the ideal shear stresses of a material, which are much less anisotropic. Therefore, as the size of a sample gets smaller, the yield stress increases and τ CRSS anisotropy decreases. Here, we use in situ transmission electron microscopy mechanical testing and atomistic simulations to demonstrate that τ CRSS anisotropy can be significantly reduced in nanoscale Mg single crystals, where extremely high stresses (∼2 GPa) activate multiple deformation modes, resulting in a change from basal slip-dominated plasticity to a more homogeneous plasticity. Consequently, an abrupt and dramatic size-induced "brittleto-ductile" transition occurs around 100 nm. This nanoscale change in the CRSS anisotropy demonstrates the powerful effect of sizerelated deformation mechanisms and should be a general feature in plastically anisotropic materials.lightweight alloys | metallurgy | mechanical properties | in situ TEM | nanoparticle S trength and ductility are critical performance indicators of materials; in metals, both are associated with the activities of line defects in the crystalline lattice, called dislocation plasticity. Ductility is accomplished by the distributed and uniform multiplication and propagation of dislocations, whereas strengthening is often achieved by hindering their motion. Strength and ductility are fundamentally linked in materials, and a mechanism to improve one almost always leads to a decrease in the other (1, 2). How to achieve both high strength and high ductility is still a challenge of great importance in structural materials. Recent work has demonstrated that it is possible to improve both strength and ductility simultaneously, but this has mostly been limited to systems with ultrafine microstructures, such as nanotwinned Cu or twinning-induced plasticity steels (3, 4).As the lightest structural metal, Mg suffers from limited room temperature ductility and formability due to the highly anisotropic critical resolved shear stress (CRSS; τ CRSS ) of the different slip systems (5). In Mg, which has a hexagonal close-packed structure, the τ CRSS for nonbasal (prismatic and/or pyramidal) slip is ∼10 2 τ CRSS for basal slip (6, 7). Such an extreme plastic anisotropy of A ≡ τ nonbasal CRSS =τ basal CRSS ∼ 10 2 makes nonbasal slip very difficult to trigger. Without nonbasal slip or twinning (8), basal slip alone cannot accommodate arbitrary shape changes, and excessive basal slip in combination with unrelaxed tensile stresses in the plane-normal direction leads to spatially localized damage and rapid failure. Thus, a materials design strategy could be to enhanc...

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Section: Discussionmentioning

confidence: 99%

Reducing deformation anisotropy to achieve ultrahigh strength and ductility in Mg at the nanoscale

Qi²,

Mishra

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

115

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“…Maximum elongation can exceed 40 pct after ECAP and subsequent annealing. [24,25] A strong texture is produced in magnesium alloys processed by ECAP. [13,26] Mukai et al [24] suggested that majority of grains change their orientation in a way such that their basal planes are coincident with a shear plane.…”

Section: Introductionmentioning

confidence: 99%

“…[25] Textural development is believed to be responsible for the decrease of yield stress and enhancement of ductility in ECAPed Mg alloys despite the significant grain refinement. Nevertheless, Mukai et al [24] also showed that ECAP followed by annealing can remarkably improve room temperature ductility of AZ31 magnesium alloy. The mean grain size obtained measured about 1 lm after ECAP and 15 lm after subsequent annealing.…”

Section: Introductionmentioning

confidence: 99%

Mechanical Properties and Microstructure of AZ31B Magnesium Alloy Processed by I-ECAP

Gzyl

Rosochowski

Pesci

et al. 2013

Metall Mater Trans A

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Incremental equal channel angular pressing (I-ECAP) is a severe plastic deformation process used to refine grain size of metals, which allows processing very long billets. As described in the current article, an AZ31B magnesium alloy was processed for the first time by three different routes of I-ECAP, namely, A, B C , and C, at 523 K (250°C). The structure of the material was homogenized and refined to~5 microns of the average grain size, irrespective of the route used. Mechanical properties of the I-ECAPed samples in tension and compression were investigated. Strong influence of the processing route on yield and fracture behavior of the material was established. It was found that texture controls the mechanical properties of AZ31B magnesium alloy subjected to I-ECAP. SEM and OM techniques were used to obtain microstructural images of the I-ECAPed samples subjected to tension and compression. Increased ductility after I-ECAP was attributed to twinning suppression and facilitation of slip on basal plane. Shear bands were revealed in the samples processed by I-ECAP and subjected to tension. Tensioncompression yield stress asymmetry in the samples tested along extrusion direction was suppressed in the material processed by routes B C and C. This effect was attributed to textural development and microstructural homogenization. Twinning activities in fine-and coarsegrained samples have also been studied.

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Section: Introductionmentioning

confidence: 99%

“…Unfortunately, Mg alloy sheets usually exhibit poor ductility at room temperature which is a significant impediment to their acceptance in industrial applications [2]. It is well known that grain refinement has a great influence on the improvement of mechanical properties of AZ31 magnesium alloys [2][3][4]. It was reported [5] that mechanical properties of AZ31 magnesium alloys were enhanced when the grain size was reduced from 9.8 m to 1.4 m. On the other hand, basal texture is another important factor which can greatly influence the mechanical properties of magnesium alloys.…”

Section: Introductionmentioning

confidence: 99%

Microstructure and texture evolution in multi-pass warm rolled AZ31 magnesium alloy

Liu

2015

MATEC Web of Conferences

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Abstract. Electron Backscatter Diffraction (EBSD) is employed to characterize the microstructure and texture established during the process of warm rolled AZ31 magnesium alloy sheets. The grain size was refined from 17.4 m to 3.8 m after 4 pass rolling. Texture of as-rolled sheets was expressed by (0002) basal texture, and the texture intensity was increased with the rolling pass increasing. The mechanical properties of as-rolled sheets were greatly improved by warm rolling.

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Ductility enhancement in AZ31 magnesium alloy by controlling its grain structure

Cited by 767 publications

References 9 publications

Reducing deformation anisotropy to achieve ultrahigh strength and ductility in Mg at the nanoscale

Reducing deformation anisotropy to achieve ultrahigh strength and ductility in Mg at the nanoscale

Mechanical Properties and Microstructure of AZ31B Magnesium Alloy Processed by I-ECAP

Microstructure and texture evolution in multi-pass warm rolled AZ31 magnesium alloy

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