Repeatability of the fatigue performance of additively manufactured A357.0 under different thermal treatment conditions

A357.0 parts were produced by laser-based powder bed fusion. An in-situ annealing strategy was applied by pre-heating the build platform, in order to relieve residual stresses and reduce anisotropic effects upon processing. The mean value and standard deviation for the fatigue strength at the given life time of 1 × 107 cycles were determined according to the staircase method, before and after T6 heat treatment. Samples parallel to the build platform and parallel to the growth direction were analysed separately and compared. The fatigue behaviour was substantially insensitive to post-processing heat treatment, since fracture initiation was governed by sub-surface lack-of-fusion defects that remained unchanged in the T6 conditions. The heat treatment caused an increase in porosity, yet without significant detriment to the fatigue resistance. The build orientation was not found to affect the average value of the fatigue strength, but it caused variations of the repeatability.