Rotating bending fatigue tests were carried out for a squeeze cast Al alloy, AC4CH-T6, to investigate the effect of flow forming on fatigue strength. By flow forming, the microstructure was crush down to the forming direction. The increase in fatigue strength was confirmed by flow forming. The effect of flow forming on the increase in fatigue strength was mainly caused by the increase in resistance to a crack growth. However the increase in fatigue strength was very small and there was no or little improvement in the scatter of fatigue strength, meaning that the application of flow forming to squeeze cast Al alloy should be considered from viewpoints of cost, equipment and so on. This was caused from that the alloy squeeze cast was essentially refined the microstructures and reduced the defects like a void.
