Abstract

Columnar-structured Mg_97.27Zn_2.54Y_0.19 alloy with the preferred growth direction of 〈22\(\bar{4}\)5〉 and 〈12\(\bar{3}\)3〉, and Mg_98.01Zn_1.84Y_0.13Zr_0.03 alloy with the preferred growth direction of 〈11\(\bar{2}\)0〉 were prepared using the directional solidification technique and then tensile tested at 250–300 °C. The results showed that the Mg_97.27Zn_2.54Y_0.19 alloy with columnar dendritic structure experienced a significant deformation strengthening period when stretched at 250 °C, and a typical dynamic recrystallization stage at 300 °C, which were mainly accounted for its well-developed secondary dendrites, a large number of branch-shaped second phases distributed in the longitudinal grain boundary, and less granular second phases existing in the crystal. While in the whole test temperature range (250–300 °C), the stress–strain curves of Mg_98.01Zn_1.84Y_0.13Zr_0.03 alloys with cellular dendritic crystals showed a steady deformation state because of the second phases with strip distributing in the longitudinal grain boundary, which was induced by a balance between the deformation strengthening and the dynamic recrystallization. Especially at 300 °C, this steady deformation state existed in the strain of 5.6%–36%. The good uniform plastic deformation was closely related to the small misorientations between columnar grains, the associated movement of grains by grain boundary slipping, and the less percentage of dynamically recrystallized grains which could do harm to the orientation continuity of the columnar crystals.

Graphic Abstract

The directionally solidified Mg_98.01Zn_1.84Y_0.13Zr_0.03 and Mg_97.27Zn_2.54Y_0.19 alloys with different orientation and grain morphology show different high temperature mechanical properties at 250 °C and 300 °C.

中文翻译：

---

晶粒形态和取向对定向凝固镁合金高温拉伸行为的影响

摘要

柱状结构的Mg _97.27 Zn _2.54 Y _0.19合金，其优选的生长方向为<22 \（\ bar {4} \） 5>和<12 \（\ bar {3} \） 3>，以及Mg _98.01 Zn _1.84 Y使用定向凝固技术制备了具有优选的生长方向为<11 \（\ bar {2} \） 0>的_0.13 Zr _0.03合金，然后在250–300°C下进行了拉伸试验。结果表明，Mg _97.27 Zn _2.54 Y _0.19具有柱状枝晶结构的合金在250°C拉伸时经历了明显的形变强化期，并且在300°C时经历了典型的动态再结晶阶段，这主要是由于其二次枝晶发达，大量的分支状第二相分布在纵向晶界，晶体中存在的第二相较少。在整个测试温度范围（250–300°C）中，Mg _98.01 Zn _1.84 Y _0.13 Zr _0.03的应力-应变曲线具有蜂窝状树枝状晶体的合金显示出稳定的变形状态，这是因为第二相在纵向晶粒边界中分布有条带，这是由变形强化和动态再结晶之间的平衡引起的。特别是在300°C时，这种稳定的变形状态存在于5.6％–36％的应变中。良好的均匀塑性变形与柱状晶粒之间小的取向不良，晶粒因晶界滑移而伴随的晶粒运动以及较少可能损害柱状晶体取向连续性的动态再结晶晶粒的百分数密切相关。

图形摘要

具有不同取向和晶粒形态的定向凝固Mg _98.01 Zn _1.84 Y _0.13 Zr _0.03和Mg _97.27 Zn _2.54 Y _0.19合金在250°C和300°C下具有不同的高温机械性能。