The present study aims to investigate the effect of weld geometry and geometrical shape imperfections on the mechanical behavior of welded joints under different post-weld heat treatment conditions. Finite element analyses were performed using the local mechanical properties of laser beam welded AA2198 joints obtained from micro-flat tensile test specimens. The finite element results show that, for the as-welded condition show that the maximum strain was observed in the lower region of the fusion zone, independently the geometrical imperfections. By applying post weld heat treatment, the maximum strain concentration can now be noticed in the upper region of the fusion zone for all the ageing times due to the lower local elongation at fracture values.