Mg-Al-Zn-Nd合金微观组织演变及稀土相强化行为

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

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元素后的实验合金主要由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相由针状向棒状转变,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: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;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对位错运动的钉扎较强;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,表明这3种相均为脆性相。相对Mg17Al12相而言,Al11Nd3和Al2Nd相的硬度较大。

The microstructure evolution of the Mg-Al-Zn-Nd alloy was characterized by XRD,SEM and TEM,and the strengthening behavior of the rare-earth-containing phases in the alloys was studied.Results show that the microstructure consists of theα-Mg,Mg17Al12,Al2Nd and Al11Nd3 phases in the experimental alloys.Meanwhile,as increases the content of Nd element,the size and the number of the Mg17Al12 phase gradually decrease;however,the number of the dispersed Al2Nd and Al11Nd3 phases increases.Moreover,the shape of the Al11Nd3 phase changes from needle-like to the rod-like with the increasing of Nd content,and the semi-coherent interface with strong binding ability exists between Al11Nd3 phase and matrix Mg.Furthermore,the strengthening behavior of the rare-earth-containing phases includes the following aspects: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.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 in pinning dislocation movement.The number increasing of the rare-earth-containing phases results in the number decreasing of the micro-cracks sources,which initiate 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,indicating these three kinds of phases are all brittle phases.Compared with the Mg17Al12,the hardness of Al11Nd3 and Al2Nd are higher.