Latest research advances on magnesium and magnesium alloys worldwide

Pure magnesium exhibits poor ductility owing to pyramidal [Formula: see text] dislocation transformations to immobile structures, making this lowest-density structural metal unusable for many applications where it could enhance energy efficiency. We show why magnesium can be made ductile by specific dilute solute additions, which increase the [Formula: see text] cross-slip and multiplication rates to levels much faster than the deleterious [Formula: see text] transformation, enabling both favorable texture during processing and continued plastic straining during deformation. A quantitative theory establishes the conditions for ductility as a function of alloy composition in very good agreement with experiments on many existing magnesium alloys, and the solute-enhanced cross-slip mechanism is confirmed by transmission electron microscopy observations in magnesium-yttrium. The mechanistic theory can quickly screen for alloy compositions favoring conditions for high ductility and may help in the development of high-formability magnesium alloys.

http://science.sciencemag.org/content/sci/359/6374/447.full.pdf

Mechanistic origin and prediction of enhanced ductility in 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.

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

Texture evolution during static recrystallization of cold-rolled magnesium alloys

Current issues in magnesium sheet alloys: Where do we go from here?

Excellent room-temperature ductility and formability of rolled Mg–Gd–Zn alloy sheets

Anomalous effects of strain rate on the room-temperature ductility of a cast Mg-Gd-Y-Zr alloy

Influence of texture and grain size on the room-temperature ductility and tensile behavior in a Mg-Gd-Zn alloy processed by rolling and forging

Microstructure and mechanical properties of a sand-cast Mg-Nd-Zn alloy

The tensile deformation behavior of Mg-3Gd-Zn (wt.%) alloy sheets annealed and aged at different temperatures has been studied. Samples annealed at 400 degrees C for 1 h exhibit serrated flow when they are tensile tested at temperatures ranging from 150 degrees C to 250 degrees C and at strain rates of 1 x 10(-4) s(-1) to 1 x 10(-2) s(-1). The critical strain for onset of the serrated flow is observed to increase with increasing strain rate but decrease with increasing temperature. The temperature dependences of yield strength and ultimate strength exhibit a plateau, and the expected ductility dips are also observed in the temperature regime of serrated flow. For samples annealed at 480 degrees C for 1 h, the precipitates and serration both disappear. However, subsequent aging treatments result in the reappearance of a large amount of precipitates and the serration phenomenon, proving that the serrated flow in the Mg-3Gd-Zn sheets is mainly controlled by the shearing of precipitates by gliding dislocations. In addition, the observed static strain aging effect, the negative strain rate sensitivity and the calculated activation energy, combined with observations made by scanning electron microscopy, suggest that dynamic strain aging may also contribute to the serrations in the present alloy. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.

Dianhua Wu

Papers

Excellent room-temperature ductility and formability of rolled Mg–Gd–Zn alloy sheets

Anomalous effects of strain rate on the room-temperature ductility of a cast Mg-Gd-Y-Zr alloy

Influence of texture and grain size on the room-temperature ductility and tensile behavior in a Mg-Gd-Zn alloy processed by rolling and forging

Microstructure and mechanical properties of a sand-cast Mg-Nd-Zn alloy

Serrated flow and tensile properties of a Mg-Gd-Zn alloy