The Influence of Strain Path on Rare Earth Recrystallization Textures in a Magnesium-Zinc-Rare Earth Alloy
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INTRODUCTION
IN recent years, there has been renewed interest in wrought magnesium alloys as part of the drive to reduce weight and hence produce greener, more fuel efficient vehicles.[1] The two primary limitations preventing the widespread uptake of magnesium alloys are low formability and poor corrosion performance. This study focuses on the first aspect, where there has been considerable research effort to extend the formability of magnesium alloy to sheet to lower temperatures, so that it becomes a commercially viable material for mass produced vehicle manufacture. To achieve this goal, two main approaches are followed, which involve either adjusting processing route or changing alloy chemistry. The discovery that small additions of rare earth (RE) elements can significantly enhance formability has led to an intense focus on these alloys.[2,3] Although there has been considerable progress in understanding the role
D. GRIFFITHS is with the TWI Ltd, Granta Park, Cambridge, CB21 6AL, UK. B. DAVIS is with the Magnesium Elektron North America Inc., 1001 College St., P.O. Box 258, Madison, IL 62060. J.D. ROBSON is with School of Materials, University of Manchester, MSS Tower, Manchester M13 9PL, UK. Contact e-mail: [email protected] Manuscript submitted February 2, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
that RE plays in producing this enhancement, a complete explanation for all the observed effects remains elusive. This is partly because RE additions have a complex influence on several microstructural mechanisms that ultimately control formability, and it is a combination of these effects that appears to give the desirable macroscopic behavior. However, it is clear that the effect of RE in weakening or changing the texture in Mg sheet is central to its effectiveness in improving formability. The origins of this texture change are themselves complex. Increased non-basal slip, a change in twining activity, changes in the size and distribution of shear bands, and modification of the dynamic and static recrystallization behavior have all been cited as important texture modifying mechanisms.[4] Furthermore, there is now good evidence that the strong segregation of RE to sites such as grain boundaries or dislocations helps explain why even very low levels of addition (
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