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Large plasticity in magnesium mediated by pyramidal dislocations

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Science  05 Jul 2019:
Vol. 365, Issue 6448, pp. 73-75
DOI: 10.1126/science.aaw2843

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Smaller but more ductile

Poor ductility is one limiting factor in widespread use of strong but lightweight magnesium alloys in cars, trains, and planes. The usual way to try to circumvent this poor ductility is by adding other elements, which can be costly. Liu et al. show that very small samples of pure magnesium are much more ductile than previously believed (see the Perspective by Proust). The small samples suppress the deformation twinning that causes fractures in larger samples. Avoiding this mechanism should allow development of high-ductility magnesium and other metal alloys.

Science, this issue p. 73; see also p. 30

Abstract

Lightweight magnesium alloys are attractive as structural materials for improving energy efficiency in applications such as weight reduction of transportation vehicles. One major obstacle for widespread applications is the limited ductility of magnesium, which has been attributed to c+a dislocations failing to accommodate plastic strain. We demonstrate, using in situ transmission electron microscope mechanical testing, that c+a dislocations of various characters can accommodate considerable plasticity through gliding on pyramidal planes. We found that submicrometer-size magnesium samples exhibit high plasticity that is far greater than for their bulk counterparts. Small crystal size usually brings high stress, which in turn activates more c+a dislocations in magnesium to accommodate plasticity, leading to both high strength and good plasticity.

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