<p>This study comparatively investigated the microstructure, fatigue performance, and fracture mechanisms of a conventionally cast alloy and a thixoformed Al-8Si alloy subjected to controlled diffusion solidification. The microstructure of the as-cast alloy was primarily composed of coarse dendritic α-Al phases and acicular eutectic Si phases. The thixoforming process promoted the formation of nearly globular primary α-Al particles, refined the eutectic Si phase, and resulted in a more uniform distribution of the phase. High-cycle fatigue tests were conducted at a frequency of 89&#xa0;Hz up to 1 × 10⁷ cycles to evaluate the fatigue performance. The thixoformed alloy exhibited a higher fatigue strength and longer fatigue life than the as-cast alloy at 1 × 10⁷ cycles. This enhancement of fatigue performance was mainly attributed to a reduction in defect density and a refined eutectic Si phase morphology during the thixoforming process.</p>