The microstructural evolution of as cast ZA27 alloy wa s investigated during compressive creep under 30 MPa at 160 ℃ by means of X ra y diffraction and SEM. The results showed that compressive creep induced decompo sition of a metastable η′ phase and the occurrence of a four phase transforma tion

α+ε→T+η

with volume expansion during testing

resulting in negativ ecreep in the alloy. The lamellar microstructure evolved into spheroidal microst ructure in the alloy with the increase in compressive creep strain

which provid ed an evidence of phase transformation during aging process.