Abstract: In order to further improve the mechanical properties of complex thin-walled aluminum alloy structural parts, especially the high temperature creep resistance, rare earth yttrium (Y) and cerium (Ce) were applied to modify ZL114A based on vacuum counter-pressure casting process. According to the experimental results of hardness, tensile properties, and creep strain, combined with the influence of rare earth elements on the evolution of the alloy microstructure, the creep mechanism and strengthening mechanism of the modified ZL114A alloy were revealed. The results indicate that the mechanical properties of alloy first increase and then decrease with the increase of Y and Ce, and the optimal addition is 0.3 wt.%. At this time, the creep stress indexes are 3.52 and 3.88 respectively, and the creep process is dominated by dislocation viscous slip. The rare earth atoms can improve the constitutional supercooling and as the core for heterogeneous nucleation which result in the grain refinement of a-Al. Meanwhile, the fragmented eutectic silicon phase changes into fibrous form and the original dendrites gradually spheroidized and developed into equiaxed crystal. Additionally, Y tends to precipitate in block form while the Ce rich phase presents as a ribbon structure, and the both elements are mainly distributed in the grain boundaries and partly dissolved in the alloy matrix. Therefore, the grain boundaries are strengthened due to the dislocation movement is hindered by the rare earth phase via pinning effect. Simultaneously, the weakening of heat resistance due to the coarsening and decomposition of Mg₂Si and the diffusion of Mg can be inhibited by Y or Ce atoms at a high temperature. The modification effect of Y is relatively better because of the different of distribution morphology which is contributed to the scale difference in Y and Ce atoms.

Key words: creep mechanism, vacuum counter-pressure casting, rare earth modification, ZL114A