La和Nd复合添加对AZ91镁合金铸态组织和性能的影响

Effects of La and Nd Co-addition on Microstructure and Mechanical Properties

摘要:

利用SEM和XRD等方法研究了总添加量为2.5%(质量分数, 下同)的单加或复合添加La和Nd的AZ91镁合金的铸态显微组织和相组成，并测试和分析了合金的室温力学性能。结果表明：单加或复合添加2.5%的La和Nd使AZ91合金中的β相Mg17Al12数量明显减少。单加La和单加Nd在AZ91合金中形成的稀土相分别是针状的Al11La3和块状的Al2Nd；二者复合加入时两种稀土相同时出现，Al11La3相和Al2Nd相的尺寸较单加时有所减小，其相对含量与两种稀土元素添加量成正比。当复合添加La和Nd时，Al11La3相中的部分La和Al2Nd相中的部分Nd分别被Nd和La置换。相对于单一添加，复合添加La和Nd能更显著地改善AZ91的力学性能。本实验研究的合金中，AZ91+1.0%La+1.5% Nd合金力学性能最好，其铸态合金的抗拉强度和延伸率分别为235 MPa和10%

Abstract:

The microstructures and phase composition of as-cast AZ91 magnesium alloys with addition of 2.5wt% RE (RE=La, La and Nd or Nd) in total were investigated by SEM/EDS and XRD. The mechanical properties of the alloys were analyzed at room temperature. The results show that the β-Mg17Al12 amount of AZ91 alloy is decreased evidently with the 2.5wt% addition of RE. The Al-RE phases of Mg-9Al-1Zn-2.5La and Mg-9Al-1Zn-2.5Nd are acicular Al11La3 and particle-like Al2Nd, respectively. Both Al11La3 and Al2Nd are formed with co-addition of La and Nd, whose sizes are smaller than those of single addition. The relative content of the two Al-RE phases is proportional to the addition content of La and Nd. Part of La in Al11La3 or Nd in Al2Nd is substituted by Nd or La respectively when La and Nd are co-added into AZ91 alloy. Compared with single addition of La or Nd, co-addition can improve the mechanical properties of as-cast AZ91 alloy more significantly. In all magnesium alloys investigated, the Mg-9Al-1Zn-1.0La-1.5Nd alloy exhibits the best mechanical properties, whose UTS is 235 MPa and d is 10% at room temperature