将固溶处理后的Mg-2.7Nd-0.6Zn-0.5Zr合金在200~300 ℃之间进行不同温度及时间的高温时效处理, 研究高温短时间时效处理对合金的微观组织和力学性能的影响, 并利用OM, SEM和TEM对合金的微观组织进行表征. 结果表明, 固溶态Mg-2.7Nd-0.6Zn-0.5Zr合金经250~275 ℃高温短时间时效后, 其室温屈服强度和抗拉强度最高分别增加了近70%和29%, 宏观组织中出现呈直线性不均匀分布的析出相. 析出相的显微形貌为颗粒状, 成分为Mg12Nd. 析出相的线性分布方向平行于Mg基体(0001)Mg基面, 合金的时效硬化行为与这种沿基面呈平行线分布的颗粒状析出相密切相关. 在250~275 ℃范围内时效20~30 min后屈服强度较高, 这是由于在变形过程中颗粒状Mg12Nd的特殊分布对基面滑移及晶粒间协调变形起到很强的抑制作用.
Among the traditional cast magnesium alloys system, Mg-3Nd-1Zn alloy with high strength and heat resistance, has been widely applied in aeronautics such as in engine box and wing rib of airplane. In present research, the as-cast Mg-2.7Nd-0.6Zn-0.5Zr (NZ31) alloy was solution treated and then aged at temperatures ranging from 200 ℃ to 300 ℃. The microstructures and mechanical properties of the aged specimens especially at relatively high temperature (225~300 ℃) were systematically characterized by OM, SEM and TEM. A new kind of precipitates distributed in line was clearly found in the specimens aged at high temperature (225~275 ℃) for a short time (15~30 min), which corresponded to a significant enhancement of hardness and tensile strength at room temperature. The TEM results showed that the precipitates distributed in line had a composition of Mg12Nd and a granular shape, and mainly formed along the (0001)Mg basal plane. The special distribution of the granular Mg12Nd precipitates was effective barriers to the basal slips and may probably restrain the intergranular coordination during tensile deformation, leading to a large strengthening effect, that is, the yield strength and ultimate tensile strength, of the NZ31 alloy aged at 250~275 ℃ for 20~30 min, increased by about 70% and 29% respectively, in comparison with only the solutionized one.
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