The microstructural evolution and superplastic behavior at low temperatures of Mg-5.00Zn-0.92Y-0.16Zr (wt.%) alloys after hot extrusion and ECAP process
The microstructural evolution and superplastic behavior at low temperatures of Mg-5.00Zn-0.92Y-0.16Zr (wt.%) alloys after hot extrusion and ECAP process
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DOI：
10.1016/j.msea.2012.03.116
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发表时间：
2012-07-15
期刊：
影响因子：
6.4
通讯作者：
Wu, K.
中科院分区：
文献类型：
--
作者：
Xu, S. W.;Zheng, M. Y.;Wu, K.
采用等通道转角挤压(ECAP)技术，对热挤压后的Mg-5.00Zn-0.92Y-0.16Zr(wt.%)合金进行了变形，获得了尺寸为0.6微米的超细晶组织和均匀分布的细小准晶Mg3YZn6。初生态合金的基面沿EPD方向倾斜约45度，从而获得沿EPD方向的(0 0 0 1)lt；1 1(2)基面滑移的高施密德因子为0.36。然后，研究了包裹态合金在150~250℃、初始应变速率为1.67×10~(-3)S(~(-1))~1.67×10~(-1)S(~(-1))的低温超塑性行为，并与挤压态合金的超塑性行为进行了比较。利用电子背散射衍射仪(EBSD)系统地研究了拉伸试验过程中的组织演变、织构演化和断裂行为。在沿EPD进行拉伸试验时，原始合金试件的基面偏离原始位置约15度，因此，基面仍处于有利于沿EPD基面滑移的位置。结果表明，在温度为200℃、应变速率为1.67×10~(-3)S(~(-1))的条件下，获得了865%的最大延伸率，这是由于这种有利的基面织构和良好的超细晶组织热稳定性的结果。这一最佳超塑温度为200℃，远低于其他Mg-Zn-Y-(Zr)合金的超塑性温度。相反，对于挤压后的合金样品，直到250℃的临界条件和1.67x10(-3)S(-1)的应变速率时才发生超塑性行为。在此温度和应变速率下，保持了较强的挤压基态织构，并观察到热加工粗化区(或未深冲加工区)的裂纹形核，主要与形成38°{1 0(1)上方棒材}-{1 0(1)上方棒材2}孪晶有关。在此温度和应变速率下，动态回复和随后的再结晶过程显著细化了热加工粗大区域。在这种情况下，双胞胎的形成被阻止了，生产被推迟了。皇冠版权所有(C)2012由爱思唯尔出版。保留所有权利。
In this study, equal channel angular pressing (ECAP) was applied to a hot-extruded Mg-5.00Zn-0.92Y-0.16Zr (wt.%) alloy to produce an ultrafine-grained a-Mg structure of 0.6 mu m with uniformly distributed fine quasicrystal Mg3YZn6 particles. The basal planes in the as-ECAPed alloy were inclined approximately 45 degrees to the ECAP direction (EPD); thus, a high Schmid factor of 0.36 for (0 0 0 1)< 1 1 (2) over bar 0 > basal slip along EPD was obtained. Then, the superplastic behavior at low temperatures of 150-250 degrees C and initial strain rates of 1.67 x 10(-3) s(-1)-1.67 x 10(-1) s(-1) of the as-ECAPed alloy was investigated and compared with that of the as-extruded alloy. The microstructural development, texture evolution and cracking behavior during tensile tests were systemically investigated by electron backscattered diffraction (EBSD) analysis. During the tensile test along the EPD, the basal planes in the as-ECAPed alloy specimen were tilted approximately 15 degrees away from the original position; thus, the basal planes were still in a position favorable for the basal slip along the EPD. As a result, a maximum elongation of 865% was obtained at 200 degrees C and a strain rate of 1.67 x 10(-3) s(-1), as a result of this favored basal texture and the excellent thermal stability of the ultrafine-grained structure. This optimum superplastic temperature of 200 degrees C is much lower than that obtained for other Mg-Zn-Y-(Zr) alloys. In contrast, for the as-extruded alloy specimen, superplastic behavior did not occur until the critical condition of 250 degrees C and a strain rate of 1.67 x 10(-3) s(-1). Below this temperature and strain rate, the strong extrusion basal texture was maintained, and the cracks in the hot-worked coarse region (or un-DRXed region) were observed nucleating mainly associated with the formation of a 38 degrees {1 0 (1) over bar 1}-{1 0 (1) over bar 2} double twin. At this temperature and strain rate, the hot-worked coarse regions were significantly refined by the dynamic recovery and the following recrystallization process. In the case, the formation of a double twin was prevented and the facture was delayed. Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved.