Heat treatment process for semi-solid thixoformed A356 alloy bush cap was optimized by orthogonal method under the condition of heating in resistance furnace. The microstructures and properties of the bush cap were examined. The results showed that optimum T6 treatment for semi-solid thixoformed bush cap is shown as follows: solid solution temperature 535 ℃ for 10h

ageing temperature 165 ℃ fo 5 h. Hardness of bush cap Hv 116.85. Meanwhile

precipitated phase is characterized by uniform distribution and fine microstructure. The existence of thixoformed zone results in strengthening effects to some extent. The properties of heat-treated thixoformed bush cap are superior to those in low-pressure casting and other semi-solid methods also.