<p>The fatigue of welded joints is a key design criterion in cyclically loaded aluminum structures. Post-weld treatments (PWTs) can be applied to overcome this issue by providing enhanced fatigue capacity in welded joints. Different PWT techniques and design recommendations are well covered for welded steel materials, while welded aluminum joints have received much less attention. This study investigates the applicability and fatigue enhancement of various PWTs in welded 5083-H111 joints in fillet-welded double-sided transverse stiffeners. Constant amplitude loading fatigue tests with the applied stress ratio of <i>R</i> = 0.1 were carried out for post-weld-treated transverse attachment joints. PWTs included residual stress modification techniques, covering high-frequency mechanical impact (HFMI) treatment (with two different process parameters) and shot peening, as well as weld geometry improvement techniques, including weld toe burr grinding and TIG dressing. The fatigue test results were compared to the as-welded reference group. The residual stresses and local weld geometries were measured from specimen series. HFMI treatment with recommended process parameters for steel joints improved fatigue capacity by a factor of 1.3, while lower intensity HFMI treatment provided a significantly higher enhancement with a factor of 2.4. TIG dressing had similar performance to low-intensity HFMI, while shot peening and weld toe burr grinding had slightly poorer performance with improvement factors of 2.2 and 2.0, respectively. The results of this study indicate the high potential of PWTs to enhance the fatigue strength of welded aluminum structures.</p>