Effects of constituent particle clusters on fatigue behavior of 2024-T3 aluminum alloy

Fatigue tests of 2024-T3 aluminum sheet were run to determine the effects of constituent particles and particle clusters on fatigue life for all three metallurgical planes. In addition, a model to account for crack coalescence within particle clusters was developed to determine if particle clusters can be more damaging than single particles as crack nucleation sites. On the LS and ST planes, cracks formed primarily at single particles or holes, indicating that coalescence was not an issue. On the LT plane, coalescence was observed when the particle clusters were aligned with the crack growth direction, and the life was reduced about 30%. The crack coalescence and growth model showed that varying the initial separation between two particles (potential cracks) causes at most about a 15–20% change in fatigue life over a separation range of 5 μm to 1200 μm for a pair of 50 μm² particles.