Abstract:The aging characteristics of as-quenched microstructures of ZA-27 alloy and SiCp/ZA-27 composite(ZMCp) were investigated using SEM, EDS and TEM. The structure, morphology and size of sub-grains in primary dendrite in ZMCp continuously change during aging process. Little tiny spherical Zn-rich η phase distributes in the dendrite. Amount of transitional α′phase, well coherent with equilibrium αf phase, in SiCp-neighboring dendrite edge zone is less than that in dendrite center zone. Both eutectic and peritectic β phase transform into lamellar α and η phases, obeying η∥[110]α, and (002)α∥ η. In the like-eutecticum of ZMCp, less amount of β phase and decomposition products are found. The size of α phase decomposed from peritectic β phase in ZMCp is obviously larger than that in the monolithic alloy. The lamella decomposition of β phase beside SiCp is evidently more rapid than that in the alloy. SiC particulates strongly accelerate neighboring β phase decomposition in aging process.

Key words: SiCp/ZA-27 composite; aging microstructure; ZA-27 alloy; precipitation; crystallographic orientation relationship