Influence of particles on short fatigue crack initiation in 2050-T8 and 7050-T74

International audienceThe mechanisms of fatigue crack initiation due to second phase particles are studied in 2050-T8 and 7050-T74 plate material. The particles in the specimens gauge lengths are imaged using SEM at the initial state. In 7050-T74, Mg2Si particles are very often cracked before any loading, whereas Al7Cu2Fe particles are not. In 2050-T8, the fraction of (Al, Cu, Fe, Mn) particles initially cracked is larger than that of Al7Cu2Fe in 7050-alloy, but lower than that of Mg2Si particles for similar sizes. For (Al, Cu, Fe, Mn) particles, the proportion of cracked particles increases when the modified shape ratio (aspect ratio including orientation versus rolling direction) increases. This effect is present but less pronounced for Mg2Si particles in 7050-T74. Fatigue cracks initiate at cracked (Al, Cu, Fe, Mn) particles in 2050-T8 alloy, and at both Al7Cu2Fe (cracked during cycling) and Mg2Si in 7050-T74 alloy