Texture Weakening Effects in Ce-Containing Mg Alloys
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INTRODUCTION
WHILE the improved room temperature ductility of wrought Mg-0.0035 at. pct Ce[1,2] is sometimes linked to non-basal slip enhancement, most researchers have concluded that the weaker texture in the Mg-Ce alloys is primarily responsible for the enhanced ductility. A number of other rare earth (RE) solute elements also induce texture weakening during hot deformation processing[3–6] or during subsequent annealing.[6] Additionally, Mg alloys with alkali earth elements have also recently been shown to exhibit texture weakening (e.g., Ca[9–11] and Sr[12]). Even though particle stimulated nucleation (PSN) was originally thought to be the mechanism for this phenomenon,[3] later studies indicated that PSN is not necessary to induce the texture weakening effect as it is observed to also occur in singlephase Mg-RE alloys.[4–8] In a recent work on hot-rolled Mg-RE alloys (where RE = Y, Ce, or Nd), it was found that richer alloys undergo texture weakening, while more dilute alloys possess a strong basal texture typical of conventional Mg alloys;[6] these results are indicated in Figure 1, which shows the (0002) basal pole texture strength as a function of the compositions studied. The transition from a strong to weakened texture is fairly sharp with increasing composition. In continuing studies of two of these alloy systems, Mg-Y[13] and Mg-Nd,[14] it was determined, through intragranular misorientation axis (IGMA) analysis, that the geometrically necessary
dislocation (GND) content of more dilute alloys is a predominately basal hai type, while the richer alloys were observed to have substantial prevalence of nonbasal hai dislocations, notably prismatic hai (hai type dislocations are represented by the Burgers vector, ~ b ¼ a=3 1120 ). For Mg-Nd, the second-phase particles were also observed,[6] and further work[14] on these alloys indicated that Zener drag was active in the richer, texture weakening alloys. The texture weakening effect occurs at lower solute compositions in Mg-Nd than in the single-phase Mg-Y alloys,[6] suggesting that Zener drag promotes the transition in DRX mechanism required to activate the texture weakening phenomena. The present work is a continued investigation on the third hot-rolled system studied in Reference 6, Mg-Ce, which shows similar texture weakening behavior as Mg-Nd and Mg-Y. Firstly, IGMA analysis was used to determine the GND content of samples of various compositions. Secondly, TEM analysis of the asdeformed samples was used to verify conclusions made on the basis of IGMA analysis. Finally, grain and particle size analyses were performed to determine if Zener drag occurs at different compositions, especially at richer compositions where the texture weakening effect is induced (Figure 1).
II. JASON P. HADORN, Graduate Researcher, RUPALEE P. MULAY, Postdoctoral Researcher, and SEAN R. AGNEW, Associate Professor, are with the Materials Science and Engineering, University of Virginia, Charlottesville, VA, 22904-4745. Contact email: [email protected] KERSTIN HANTZSCHE, Graduate
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