Effects of cooling velocity on multiaxial fatigue behavior of A319 alloy under circular loading conditions

The effects of cooling velocity on the multiaxial fatigue properties of A319 alloy under circular loading conditions was studied by using the MTS809 servo-hydraulic testing system and scanning electron microscopy. The results indicate that the solidification cooling velocity of 10℃·s^-1 leads to decrease in the size of microstructures, such as second dendrite arming space, Si particle, and void compared. Hysteresis loops with smaller second dendrite arming space show that there is almost no phase angle between strain and stress along the axial direction. Furthermore, the decrease in second dendrite arming space size manifests as a more remarkable additional hardening effect compared to that of the sample with a cooling velocity of 0.1℃·s^-1. The local regions of crack initiation are completely different. The cracks in samples solidified at a cooling velocity of 10℃·s^-1 initiate and propagate from large Si particulars, in contrast to the cracks in samples solidified at a cooling velocity of 0.1℃·s^-1, which initiate from pores. It is also found the A319 samples under the two different cooling velocities show initial cyclic hardening followed by cyclic softening in the axial direction and initial cyclic hardening followed by stable tendency in the shear direction.