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Through comparative study with normal casting, the effects of semi-solid thixo-extrusion on microstructures and mechanical properties with modification treatment and heat treatment of ZA27 alloys were studied. The results show that the density of semi-solid thixo-extrusion ZA27 alloy increases by 3% compared to the one obtained by normal casting, fine spherical uniform microstructure is obtained by Sc modification treatment or semi-solid thixo-extrusion, and the best roundness of the globular grains is obtained by Sc modification combined with semi-solid thixo-extrusion. The microstructure of ZA27 alloy by semi-solid thixo-extrusion combined with T6 heat treatment is composed of small α primary phase and (α+η) eutectoid phase, which shows that semi-solid thixo-extrusion can promote the dissolution of ε phase and reduce (β+η+ε) ternary eutectic content. The mechanical properties test indicates that the tensile strength, elongation and Brinell hardness of the ZA27 alloy by semi-solid thixo-extrusion, and after Sc modification and T6 heat treatment, are up to 586.01MPa, 17.57% and 171HB respectively.