稀土Ce对新型Al-Cu-Li合金力学性能与组织的影响

Effects of Trace Addition of Cerium on Microstructure and Mechanical Properties of Novel Al-Cu-Li Alloy

对一种含有不同量微量Cerium的新型高Cu/Li比的Al-Cu-Li合金经过T6和T8热处理后的硬度和拉伸性能进行了测试,同时对该合金峰时效的显微组织进行了观察。结果表明:随着含Cerium量的增加,立方相和T1相的数量均在增加,θ′相数量减少。主要因为微量Cerium加入后,Cerium会以固溶态的形式存在,如果分布于{100}面和{111}面,将会有利于立方相和T1相的析出;同时,微量Cerium的加入抑制了Cu原子的扩散、GP的形成和最终θ′相的析出;T8态时,θ′相和T1相存在竞争析出关系,随Cerium含量的增加,T1相与θ′相的相对含量比会增加。利用IPP软件对T6态峰时效的各析出相的单位面积数密度,以及θ′相和T1相的尺寸分布进行了统计。统计发现:随Cerium含量的增加,总的形核点在增加;2#(0.15%Ce)合金θ′相尺寸比1#(0%Ce)合金更加均匀,这是因为1#合金中的θ′相与立方相之间存在竞争析出关系;3#(0.3%Ce)合金T1相尺寸比2#(0.15%Ce)合金更均匀,据此分析认为,时效初期3#合金比2#合金T1相形核点更多,可以推断,时效16 h时,2#合金的立方相发生了溶解,同时,T1相出现二次析出和快速生长。

The hardness and mechanical properties of the novel AI-Cu-Li alloys containing different contents of Ce and subject to T6 and T8 heat treatments were tested. The microstructures were observed. The experiment results show that with the increase of the content of cerium and the area density of cubic phase as well as T1 phase, but the area density of θ＇ phase decreases. Which is attributed to the trace addition of cerium Ce will exist in the form of solid solution and is distributed at { 100} matrix face and { 111 } matrix face, respectively. The increase of density for the cubic phase and T1 phase between different cerium contents is due to the introduction of heterogeneous matrix nucleation sites at { 100} matrix face, and { 111 } matrix face separately. In addition, the trace cerium element is thought to tie up vacancies which restrict the Cu diffusion that is necessary for GP zone formation and θ＇ precipitate at last. The pre-age deformation significantly affects the competitive precipitation between T1 and θ＇. The relative content fraction of T1 and θ＇ greatly increases with increasing of amount of cerium. The variation of precipitate type was determined by TEM, The area density and the size of the major strengthening precipitates were obtained by Image-Pro Plus （IPP） software. It Is indicated that the total nucleation sites increase with the enhancement of the content of cerium. The uniformity of size for θ＇ phase is different for 1# and 2# alloy, that is attributed to the competitive precipitation between cubic phase and θ＇ phase at 1# alloy. The well-distributed enhancement of T1 phase size at 3# alloy directly is correlated with the obvious increase of the area density of T1 nucleation sites. It can be concluded that the dissolution of cubic phase occurs during the initial aging （T6, 180 ℃, 16 h）, at the same time, the spurting reprecipitation and growth of T1 phase happen.