Mg-Al-Zn-Nd合金微观组织演变及稀土相强化行为研究

Study on The Microstructure Evolution and The Strengthening Behavior of Rare-earth-containing Phases in Mg-Al-Zn-Nd Alloy

摘要:

本文采用XRD、SEM和TEM等方法表征了Mg-Al-Zn-Nd合金微观组织演变，研究了合金中稀土相的强化行为。结果表明：添加Nd元素后的试验合金主要由α-Mg、Mg17Al12、Al2Nd和 Al11Nd3组成。随着Nd含量的增加，Mg17Al12相尺寸变小，数量减少，弥散分布的Al2Nd和 Al11Nd3相增多，Al11Nd3相由针状趋于棒状转变，且Al11Nd3相与基体存在结合能力较强的半共格界面。稀土相强化行为表现为：（1）在拉伸过程中稀土相周围应力集中的增大，可能诱发其周围基体形成孪晶结构，可以协调部分外界应变能的增加；（2）相比Mg17Al12而言，具有较好结合能力的硬质稀土相不易萌生裂纹，且呈弥散分布的稀土相钉扎位错运动较强；（3）稀土相的增加导致基体与α+β共晶组织（M/E）界面、岛状Mg17Al12相微裂纹源的数量减少。最后，计算并简要讨论了Mg17Al12、Al2Nd和 Al11Nd3相的力学特性。

Abstract:

In this paper, the microstructure evolution of the Mg-Al-Zn-Nd alloys were characterized by XRD, SEM and TEM, and the strengthening behavior of the rare earth phases in the alloys was studied. Results show that the microstructure consists of the α-Mg, Mg17Al12, Al2Nd and Al11Nd3 phases in the experimental alloys. Meanwhile, as the content of Nd element increasing, the size and the number of the Mg17Al12 phase gradually decrease, however, the number of the dispersed Al2Nd and Al11Nd3 phases increase. Moreover, the shape of the Al11Nd3 phase changes from needle-like to the rod-like with the Nd increasing, and the semi-coherent interface between Al11Nd3 phase and matrix Mg exists strong binding ability. Furthermore, the strengthening behavior of the rare-earth-containing phases includes the following aspects: (1) During tension, the increase of stress concentration around the rare-earth-containing phases may induce the formation of twin around the matrix Mg, which can coordinate the increase of some external strain energy. (2) Compared with Mg17Al12 phase, the hard rare-earth-containing phases with good binding ability initiate micro-cracks hardly, therefore, the dispersed rare-earth-containing phases play an important role of pinning dislocation movement. (3) The increasing number of the rare-earth-containing phases results in the decreasing number of the micro-cracks sources, where the micro-cracks sources initiated at the interface between matrix and eutectic structure (M/E), as well as the island-like Mg17Al12 phase. Finally, the mechanical properties of the Mg17Al12, the Al2Nd and the Al11Nd3 phases were calculated and briefly discussed.