Aluminium AA6351 alloy is extensively used for defense and marine applications due to a better combination of strength to weight ratio and corrosion resistance. Welding is a commonly used fabrication process for manufacturing components required for shipbuilding and defense applications. The welding process affects mechanical properties and corrosion resistance because of microstructural changes in various zones of welds. In the present work, an attempt has been made to study the effect of post weld heat treatment (PWHT) of solutionising followed by ageing at 177⁰C for 8hrs on AA6351 welds made using Gas Tungsten Arc Welding (GTAW) process. This study comprises the mechanical and pitting corrosion behavior of as welded and post weld heat treated samples with respect to the microstructural changes. Microstructural studies were carried out using optical, scanning electron microscopy (with EDS) and X-ray diffraction (XRD) for various zones like fusion zone (FZ), heat affected zone (HAZ) of welded AA6351 plates. Micro-vickers hardness (at 500g load) and tensile test was carried out to analysis mechanical behaviour. Similarly, potentio-dynamic polarization testing was carried out in various zones present in the welds to understand the pitting corrosion behavior. Results revealed that the PWH treated GTA welds of AA6351 alloy exhibited a better combination of mechanical properties and corrosion resistance.