Grain-Size Strengthening in Equal-Channel-Angular-Pressing Processed AZ31 Mg Alloys with a Constant Texture

Kim, Woo Jin; Jeong, Heon

doi:10.2320/matertrans.46.251

Cited by 110 publications

(50 citation statements)

References 16 publications

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“…This is because besides the grain size, the mechanical properties can also be possibly influenced by the crystallographic texture. 25,26) Previous studies have suggested that most of the basal planes are inclined to be 45 from the extrusion direction along the shear plane below processing temperature of 523 K while tend to be parallel to the extrusion direction above 573 K. 27) This formation of 45 angle below 523 K causes the basal planes to slip easier due to the maximum imposed shear force, which as a result, retards the increase of strength originated from the largely decreased grain size at 523 K. 28) Further, by comparing our data with available reports, we found that our yield stress of 192 MPa at 523 K is larger than that of 160 MPa 29) and 130 MPa 30) obtained by 6 repetitive ECAEs, and that of 160 Mpa 24) by the hot extrusion. Additionally, the UCS of 386 MPa and compressive ratio of 14.4% at 523 K are also comparable to corresponding values of 370 MPa and 15% for the hot-extruded AZ31.…”

Section: )supporting

confidence: 47%

Change-Channel Angular Extrusion of Magnesium Alloy AZ31

Liu

et al. 2009

Mater. Trans.

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We report microstructure evolution and mechanical properties of Mg alloy AZ31 processed by a new severe plastic deformation technique, the change-channel angular extrusion (CCAE). Under all of the processing temperatures ranging from 523 to 723 K, grains of the extruded Mg alloys are found to be refined significantly, which is attributed to the grain subdivision and dynamic recrystallization induced by the drastic deformation. We have also found that lowering processing temperature is a relevant factor in yielding finer grain, which as a consequence, gives rise to higher micro-hardness, larger yield and ultimate compressive strength, and more enhanced compressive ratio. The improved mechanical properties of the AZ31 alloys deformed by the CCAE are comparable or even superior to those of the alloys subjected to the equal-channel angular extrusion with several passes, rendering the CCAE an effective and promising approach to impose drastic plastic deformation for further enhancing workability of Mg alloys.

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Section: )supporting

confidence: 47%

Change-Channel Angular Extrusion of Magnesium Alloy AZ31

Liu

et al. 2009

Mater. Trans.

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“…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). By eliminating the complicating effects of grain boundaries and compatibility from neighboring grain orientations, our in situ TEM experiments revealed the intrinsic size dependence of plastic anisotropy and offered clear evidence that it is indeed possible to achieve both high strength and high ductility by tuning the external dimensions of the sample.…”

Section: Discussionmentioning

confidence: 84%

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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“…In Mg alloys, for instance, the AZ31 alloy [46], the texture even takes the dominant position in strengthening contributions to the yield strength (see Ref [47,54] for more examples). Consequently, Mg samples with a strong texture can show significant hardness anisotropy, as was revealed for our samples in Fig.…”

Section: Anisotropic Hardness and Strength Of Mgmentioning

confidence: 99%