Christopher D. Barrett

A review on the effect of rare-earth elements on texture evolution during processing of magnesium alloys

Magnesium, the lightest structural metal, is approximately four times lighter than steel—the most widely used metal in industrial applications. Currently available Mg alloys, however, are impractically expensive for use in automotive structural components, as severe ductility problems require forming operations at elevated temperatures and an exclusion from critical safety components. With a strong impetus in research having sprung up during the last two decades, addition of rare-earth elements in small quantities emerged as a potential solution for simultaneously delivering the ductility and weight requirements for automotive applications. These improvements are arguably achieved by virtue of texture weakening and enhancement of non-basal slip. However, ways by which rare-earth elements modify texture remain very elusive, and no consensus on the driving mechanisms has been reached in the literature as of yet. We take a look back at different paradigms held for the action of rare-earth additions, and examine key facts that may reconcile controversies. We attempt to identify critical gaps and suggest venues to overcome them. These gaps, once filled, may promote Mg alloys to become a stronghold for lightweighting, which will exceptionally benefit our environment and wellbeing.

The candidacy of shuffle and shear during compound twinning in hexagonal close-packed structures

This paper proposes a systematic generalized formulation for calculating both atomic shuffling and shear candidates for a given compound twinning mode in hexagonal closed-packed metals. Although shuffles play an important role in the mobility of twinning dislocations in non-symmorphic crystals, their analytical expressions have not been previously derived. The method is illustrated for both flat planes and corrugated planes which are exemplified by {112¯2} and {101¯2} twinning modes, respectively. The method distinguishes between shuffle displacements and net shuffles. While shuffle displacements correspond to movements between ideal atom positions in the parent and twin lattices, net shuffles comprise contributions from shear on overlying planes which can operate along opposite directions to those of shuffle displacements. Thus, net shuffles in the twinning direction can vanish in a limiting case, as is interestingly the case for those needed in the second plane by the b4 dislocation candidate in {112¯2} twinning. It is found that while shuffle displacement vectors can be irrational when K1 is corrugated, net shuffle vectors are always rational.

Unraveling Recrystallization Mechanisms Governing Texture Development from Rare-Earth Element Additions to Magnesium

Abstract The origin of texture components often associated with rare-earth element (REE) additions in wrought magnesium alloys is a long-standing problem in magnesium technology. While their influence on the texture is unquestionable, it is not yet clear why certain texture components, such as

Transmutation of Basal Dislocations by \{ 1\,0\,{\bar{\text{1}}\,\text{2}}\} Twinning in Magnesium

\langle 11\bar{2}1 \rangle ||{\text{extrusion}}\;{\text{direction}},

Measurement of Twin Formation Energy Barriers Using Nudged Elastic Band Molecular Statics

⟨112¯1⟩||extrusiondirection, are favored over other components typically observed in traditional magnesium alloys. The objective of this research is to identify the mechanisms accountable for these RE textures during early stages of recrystallization. Electron backscattered diffraction and transmission electron microscopy analyses reveal that REEs in zinc-containing magnesium alloys corroborate discontinuous dynamic recrystallization. REEs promote isotropic growth for all nuclei generated through the bulging mechanism. During nucleation, the effect of REEs on orientation selection was explained by the diversified activity of both

The MEAM parameter calibration tool: an explicit methodology for hierarchical bridging between ab initio and atomistic scales

\langle 10\bar{1}0 \rangle