Effect of microstructure on fatigue crack deviation in AA2050-T84

Precipitation hardened AA2050 exhibits an unusual crack deviation phenomenon during fatigue testing: when the intended propagation direction is not parallel to macroscopic rolling direction, after initial perpendicular loading deviates and further abnormally propagates in other which can be of applied loading. Such a behaviour renders difficult prediction cracking and, thus, lifetime. In present work using multi-scale microstructure characterization (SEM/EBSD/EDS, transmission electron microscopy (TEM) atom probe tomography (APT)) AA2050-T84 tests, effect different parameters on carefully investigated keeping constant mechanical conditions (sample geometry, amplitude, frequency). The respective influence grain structure (including that boundaries), intermetallics precipitate-free zones evaluated. boundaries with misorientation angle ranging from 40 60° are observed origin phenomenon: principal at along boundary. Numerous Fe- Mn-rich found volume do represent major cause for deviation, although, fostering it (only 25% cracks were deviate regions containing intermetallics). failure was deduced APT results TEM observation precipitate free comparing T84 T34 states (the latter reveal deviation). addition, because unrecrystallized state AA2050-T84, grains feature “layered” strained favourable inside critical internal reached path. • Fatigue mostly occurs GBs. GBs weakened by PFZ and/or solute GB segregation. Grains have grains.