Analysis of the Deformation Behavior of Magnesium-Rare Earth Alloys Mg-2 pct Mn-1 pct Rare Earth and Mg-5 pct Y-4 pct Rare Earth by In Situ Energy-Dispersive X-ray Synchrotron Diffraction and Elasto-Plastic Self-Consistent Modeling MARTIN LENTZ, MANUELA KLAUS, RODRIGO S. COELHO, NOBERT SCHAEFER, FLORIAN SCHMACK, WALTER REIMERS, and BJØRN CLAUSEN The deformation behavior of the Mg-RE alloys ME21 and WE54 was investigated. Although both alloys contain rare earth elements, which alter and weaken the texture, the flow curves of the alloys deviate significantly, especially in uniaxial compression test. Apart from the higher strength of the WE54 alloy, the compression flow curve does not exhibit the typical sigmoidal shape, which is associated with tension twinning. However, optical microscopy, X-ray texture measurements, and EBSD analysis reveal the activity of tension twinning. The combination of in situ energy-dispersive X-ray synchrotron diffraction and EPSC modeling was used to analyze these differences. The investigation reveals that twin propagation is decelerated in the WE54 alloy, which requires a change of the twinning scheme from the ‘finite initial fraction’ to the ‘continuity’ assumption. Furthermore, an enhanced activity of the hc+ai pyramidal slip system was observed in case of the WE54 alloy. DOI: 10.1007/s11661-014-2533-5 Ó The Minerals, Metals & Materials Society and ASM International 2014 I. INTRODUCTION IN recent years, numerous studies revealed the possibility to alter and weaken the texture of magnesium wrought alloys by alloying rare earth (RE) elements. [1–5] Ball and Prangnell [5] investigated extrusions of the WE54 alloy and observed an uncommonly small anisot- ropy in tension and compression tests, which was attributed to a random texture. Stanford et al. [1–3] showed in a series of publications that alloying RE elements alters the texture producing the so-called rare earth texture component with the 11 21   direction parallel to the extrusion direction and thereby enhance the ductility. [1,2] These publications as well as further investigations showed that the extent of the texture change associated with alloying depends on the rare earth element and is related to the solid solubility of the RE element. [2–4] In this study, the deformation behavior of ME21 (2 wt pct Mn, 0.7 wt pct Ce) and WE54 (5 wt pct Y, 1.6 wt pct Nd, 2.6 wt pct heavy RE elements) extrusions was analyzed in uniaxial tension and compression tests. Although both alloys exhibit very weak textures, the asymmetry of the yield strength and of the subsequent flow curve deviates significantly. In order to clarify the origin of the differences of the deformation behavior in situ energy-dispersive X-ray synchrotron diffraction and elasto-plastic self-consistent (EPSC) modeling were conducted. Thereby, the hardening parameters of each deformation mode as well as the activity of the deformation modes as a function of the applied strain and the strain path were obtained. The applied EPSC model was developed by Turner and Tome´ and is based on the Eshelby inclusion formalism, which is used to represent the interaction of each grain with a homogeneous effective medium (HEM). [6] Within the model, the HEM represents the properties of the bulk material. In order to describe the evolution of the critical resolved shear stress of each deformation mode within one grain, a Voce hardening law is used [7–9] : s s ¼ s s 0 þðs s 1 þ h s 1 CÞ 1  exp  h s 0 C s s 1     : ½1 Thereby, the hardening of each deformation mode is given by the initial critical resolved shear stress s s 0 , the initial and the final hardening rate h s 0 and h s 1 , the accumulated shear strain on the deformation mode C , MARTIN LENTZ, Research Associate, FLORIAN SCHMACK, Student, and WALTER REIMERS, Chair, are with the Metallische Werkstoffe, Technische Universita¨t Berlin, Ernst-Reuter-Platz 1, 10587 Berlin Germany. Contact e-mail: martin.lentz@tu-berlin.de MANUELA KLAUS, Scientist, is with the Microstructure and Residual Stress Analysis, Helmholtz Zentrum Berlin fu¨ r Materialien und Energien, Albert-Einstein-Straße 15, 12489 Berlin, Germany. RODRIGO S. COELHO, Associate Professor, Head, formerly with the Microstruc- ture and Residual Stress Analysis, Helmholtz Zentrum Berlin fu¨ r Materialien und Energien, is now with the Departamento de Materiais, SENAI - CIMATEC, Av. Orlando Gomes 1845, Piata˜ , Salvador, BA 41650-010, Brazil. NOBERT SCHAEFER, Scientist, is with the Nanoarchitectures for Energy Conversion, Helmholtz-Zentrum Berlin fu¨ r Materialien und Energien, Hahn-Meitner-Platz 1, 14109 Berlin, Germany. BJØRN CLAUSEN, Scientist, is with the LANSCE-LC, Los Alamos National Laboratory, Los Alamos, NM 87545. Manuscript submitted June 11, 2013. Article published online September 4, 2014 METALLURGICAL AND MATERIALS TRANSACTIONS A VOLUME 45A, NOVEMBER 2014—5721