Microstructure and mechanical behaviour of an elevated temperature Mg-rare earth based alloy

Bettles, Colleen Joyce; Gibson, Mark; Zhu, Su-Ming

doi:10.1016/j.msea.2008.11.004

Cited by 92 publications

(32 citation statements)

References 21 publications

(22 reference statements)

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“…Many mechanisms have been proposed, all of which invoke extrinsic effects such as "heating" by the electron beam 8 , vacancy and self-interstitial precipitation 21 , and dislocation obstacles of "unknown" nature 7 . Also surprisingly, when loaded at slow strain rates (∼10 −1 -10 −5 /s), and particularly under compression, the yield strengths of both single crystal Mg 8,15-17 and polycrystal Mg alloys 22,23 show an increasing strength with increasing temperature, i.e. anomalous temperature dependence, within a certain temperature range.…”

Section: Introductionmentioning

confidence: 97%

The origins of high hardening and low ductility in magnesium

Curtin

2015

Nature

538

170

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Magnesium is the ultimate lightweight structural metal but exhibits low ductility connected to unusual, mechanistically-unexplained, dislocation/plasticity phenomena, which make it difficult to form and use in energy-saving lightweight structures. Here, long-time molecular dynamics simulations using a DFT-validated interatomic potential reveal the fundamental origins of the previouslyunexplained phenomena and show a clear path toward design of new ductile magnesium alloys. The key c + a dislocation is metastable on easy-glide pyramidal II planes and undergoes a thermallyactivated, stress-dependent transition to one of three lower-energy, basal-dissociated immobile dislocation structures, which (i) cannot contribute to plastic straining and (ii) serve as strong obstacles to the motion of all other dislocations. The transition is intrinsic to magnesium, driven by reduction in dislocation energy and predicted to occur at very high frequency at room temperature, thus eliminating all major dislocation slip systems able to contribute to c-axis strain and leading to its low ductility.Enhancing ductility can thus be achieved by delaying, in time and temperature, the transition from the easy-glide metastable dislocation to the immobile basal-dissociated structures, and our results provide the underlying insights needed to guide the design of ductile magnesium alloys. * Corresponding author: william.curtin@epfl.ch 1 This is a post-print of the following article: Wu, Z. & Curtin, W. A. The origins of high hardening and low ductility in magnesium. Nature 526, 62-67 (2015). The final publication is available at http://dx.doi.org/10.1038/nature15364Developing lightweight structural metal is a crucial step on the path toward reduced energy consumption in many industries, especially automotive 1,2 and aerospace 3 . Magnesium (Mg) is the ultimate lightweight metal, with a density 23% that of steel and 66% that of aluminum, and so has tremendous potential to achieve energy efficiency 4 . In spite of this tantalizing property, Mg generally exhibits low ductility, insufficient for the forming and performance of structural components. The low ductility is associated with the inability of hexagonally-close-packed (hcp) Mg to deform plastically in the crystallographic c direction, which is accomplished primarily by dislocation glide on the pyramidal II plane with the c + a Burgers vector 5 (see Fig. 1).Experiments reveal a range of unusual, confounding, conflicting, and mechanistically-unexplained phenomena connected to c+a dislocations that coincide with the inability of Mg to achieve high plastic strains 6 . Uncovering and controlling the fundamental behavior of c + a dislocations is thus the key issue in Mg, and any solution would catapult Mg science, technology, and applications forward. Success would enable, for instance, lightweight automobiles that would consume less energy, independent of the energy source, and thus act as a multiplier for many other energyreduction strategies.Due to its critical importance and pro...

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Section: Introductionmentioning

confidence: 97%

The origins of high hardening and low ductility in magnesium

Curtin

2015

Nature

538

170

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“…Currently, the most commonly used RE containing alloys are AE42 and AE44, which both contain 4 wt.% Al and also 2 wt.% and 4 wt.% RE respectively. However, recently some alloys have been developed where the RE elements are the pre-dominant alloying addition, such as the sand-cast alloy AM-SC1 [9,10] and HPDC alloys in the Mg-RE-Zn system [11,12]. RE additions have generally been regarded as expensive alloying additions; however, some elements are a lot cheaper than others [13] and selection of these could make Mg-RE based alloys more cost-competitive.…”

Section: Introductionmentioning

confidence: 99%

The effect of alloy composition on the microstructure and tensile properties of binary Mg-rare earth alloys

et al. 2009

Self Cite

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“…[23][24][25][26] Earlier works also found that the yield asymmetry of the weakly textured magnesium alloys at high temperature may be related to the different mobility behavior of <cþa> dislocations under tension and compression. [22,27,28] As explained by Hidalgo-Manrique, [22] dynamic strain aging (DSA) is related to the yield asymmetry, and the RE elements will enhance the phenomena even at higher temperatures.…”

Section: Tension-compression Yield Asymmetrymentioning

confidence: 98%

High‐Temperature Tensile and Compressive Behavior of Peak‐Aged Sand‐Cast Mg–10Gd–3Y–0.5Zr Alloy

Chen

Liu

et al. 2015

Adv Eng Mater

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The uniaxial tensile and compressive behavior of the peak-aged sand-cast Mg-10Gd-3Y-0.5Zr alloy from 25 to 250 C is investigated. The results show that the alloy exhibits excellent high-temperature tensile and compressive properties compared with other magnesium alloys. The tensile yield stress and ultimate tensile strength remain unchanged, while the compressive yield strength slightly increases when testing temperature rises from 25 to 150 C. This can be attribute to the metastable b 0 (cbco) phase and the fine ductility of the alloy at high temperature. The alloy shows tension-compression yield asymmetry which could be associated to the pyramidal slip and extension twinning. In addition, the fracture mechanisms of the tested alloy at different temperatures are studied systematically.

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Microstructure and mechanical behaviour of an elevated temperature Mg-rare earth based alloy

Cited by 92 publications

References 21 publications

The origins of high hardening and low ductility in magnesium

The origins of high hardening and low ductility in magnesium

The effect of alloy composition on the microstructure and tensile properties of binary Mg-rare earth alloys

High‐Temperature Tensile and Compressive Behavior of Peak‐Aged Sand‐Cast Mg–10Gd–3Y–0.5Zr Alloy

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