Abstract: Heated in a resistance furnace, the solution aging treatment was conducted to the specimens of thixoformed pieces of semi-solid A356 alloy, and the microstructure and properties were investigated. The results show that the strengthening phase is dissolved sufficiently, the alloy elements are distributed uniformly in lattices and the strength is improved along with the prolonging time for solution-aging treatment at 535°C. If aging at 180°C, the strength can be improved further along with the prolonging time for aging till reaching its maximum value. When exceeding the time point, the time prolongs continuously, and the alloy specimens start softening. The occurrence of the distortion zone in thixoforming process plays an important role in alloy strengthening.