The reliability of aluminum 6060 T6 is crucial in harsh marine environments. Welding affects mechanical properties, particularly in the heat-affected zone (HAZ), where thermal cycles induce over-aging and micro-structural changes. Post-weld heat treatment (PWHT) is typically applied to restore mechanical integrity; however, its effectiveness in this context remains uncertain. This study evaluated the impact of multi-pass tungsten inert gas (TIG) welding and post-weld heat treatment (PWHT) on the microstructure and mechanical properties. It also assessed the effectiveness of heat treatment in mitigating strength reduction caused by welding. Tensile testing, Vickers hardness measurements, light optical microscopy (LOM), and scanning electron microscopy (SEM) were performed on samples welded with 4043 and 5356 filler materials. Mechanical and microstructural variations concerning welding conditions and heat treatment parameters were analyzed. Results showed that 5356 filler material provided higher strength than 4043 due to its aluminum-magnesium composition. Furthermore, 5356 filler material exhibited greater ductility, whereas 4043 filler material had more welding defects, mainly porosity in the fusion zone (FZ). The HAZ closest to the fusion line was the softest due to thermal exposure, with hardness gradually increasing further from the weld zone. PWHT did not improve mechanical properties, as additional heat exposure intensified the over-aging effect and increased HAZ length. These findings highlight the need for optimized PWHT parameters and welding strategies to improve mechanical performance. The results may help refine welding procedures for 6060 T6 aluminium. Furthermore, studies are required to investigate alternative heat treatment approaches and their influence on strength recovery.