Developing a Basal Texture with Two Peaks Tilting Towards the Transverse Direction in Hot Rolled Mg-5.7Zn-0.5Zr Plates
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MAGNESIUM alloys have great potential to be used in automotive and aerospace industries for weight saving. Due to a hcp structure, basal slip and 1012 twinning constitute the main deformation modes at room temperature. At a temperature above 493 K (220 °C), non-basal slips including prismatic hai slip, pyramidal hai slip or pyramidal hc + ai slip can be initiated in a large amount.[1–3] Addition of rare earth elements (e.g., Gd or Ce) seems to increase the activity of non-basal slip at room temperature.[4,5] A strong basal texture with basal poles largely parallel to the ND usually develops in hot or cold rolled plates.[6–9] This basal texture greatly reduces the deformation ability along the thickness direction due to restricting the activity of slips of hai dislocation.[1] In most cases, a basal texture with double peaks slightly tilting from the ND towards the rolling direction (RD) forms in rolled Mg plate.[10–13] This RD-tilted basal texture results in an obvious in-plane mechanical anisotropy. For example, tensile yield strength along the RD of an AZ31 plate is often 15-20 pct lower than that along the TD.[14] Besides the spreading of basal poles YANNAN WANG and HUIHUI YU, Ph.D. Candidates, YUNCHANG XIN, and QING LIU, Professors, and ADRIEN CHAPUIS, Lecturer, are with the School of Materials Science and Engineering, Chongqing University, Chongqing 400044, China. Contact e-mail: [email protected] Manuscript submitted January 29, 2016. Article published online June 15, 2016 4276—VOLUME 47A, AUGUST 2016
from the ND towards the RD, many recent studies report the formation of double-peaked basal textures with the (0002) poles obviously tilting from the ND towards the TD during hot rolling of some Ca-containing Mg-Zn alloys (Mg-(1.5, 3)Zn-0.1Ca,[15,16] Mg-1Zn1Ca and Mg-6Zn-1Ca[17]) or many RE-containing Mg-Zn alloys (Mg-2Zn-(0.1, 0.3, 0.7)Gd,[18] Mg-1.2Zn0.79Gd,[19] Mg-1.1Zn-1.7Gd,[5] Mg-(0.5, 2.5)Zn-0.2 Ce,[20,21] Mg-1Zn-(0.3, 0.6, 1.0)Ce,[22] Mg-1Zn-1Ce,[23] Mg-1.5Zn-0.2Y,[24] Mg-0.61Zn-0.58Nd[25]). It is interesting that plates which developed a TD-tilted basal texture often have a better stretch formability or cold working ability.[21,26] Zn seems to play an important role in the formation of this TD-tilted basal texture. For example, Zn addition in Mg-Ce, Mg-Y, Mg-Nd, and Mg-Ca binary alloys will lead to a transition from a RD-tilted basal texture to a TD-tilted one in the as-rolled and annealed plates.[12,27,28] However, a double-peaked TD-tilted basal texture is scarcely reported to appear in Mg-xZn binary alloys.[29] In the present study, a basal texture with the two peaks obviously tilting from the ND towards the TD is developed in ZK60 plates after a single pass hot rolling at 673 K (400 °C) from the as-cast condition. The influence of rolling reduction and annealing treatment on microstructure and texture were systematically studied. Crystal plasticity simulation was used to understand the effect of slips and twinning on the formation of this TD-tilted basal texture. The possible mechanisms that
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