Hot-extruded 7075 aluminum alloy was used to form deep cavity cylinders by thixoextrusion. The effects of isothermal temperature and soaking time on the microstructure and mechanical properties of the formed parts were analyzed. The parameters of T6 heat treatment were optimized by orthogonal test, and the influence of T6 heat treatment on the microstructure and mechanical properties of the formed parts was studied. The results indicated that the deep cavity cylinder with a smooth surface could be successfully formed through thixoextrusion. The forming temperature and heating time had remarkable effects on the metallographic structure of the formed components. T6 heat treatment could greatly enhance the mechanical properties of the deep cavity cylinders. The optimum parameters of T6 heat treatment were achieved as: solution at 465 °C for 16 h and aging at 150 °C for 16 h. When semi-solid billets were heated at 600 °C for 10 min, the formed deep cavity cylinder had the best mechanical properties with the ultimate tensile strength of 573.57 MPa, the elongation of 13.44%, and the microhardness of HV 187.12.