The aim of this study was to investigate the effect of the welding heat input on the heat affected zone (HAZ)in AA6005-T6 aluminium alloy for a butt-welded joint using gas metal arc welding by evaluating the thermal cycles, metallography and the resulting mechanical properties in the zone. This study involved using a welding experiment, numerical simulation, physical simulation and mechanical tests. The welding was carried out using the pulsed gas metal arc welding (GMAW) transfer and type J thermocouples were used to get the thermal cycles in the HAZ. Simufact® Welding was utilised for the numerical simulation. Optical microscope was used to evaluate the microstructures and Vickers microhardness test was done along the weld cross-section. The thermal cycles of thealuminium alloy and a thermal model for the experimental setup was developed. The HAZ was located on the weld cross-section with a mean hardness of 63.7HV0.1, which is considerably lower when compared with the base metal which has a hardness of 100HV0.1. This indicates thermal softening occurred due to the heat input to the material. There is a match in the hardness values of the Gleeble samples and the locations on the weld cross section suggested by the model showing validity of the simulation. This thesis work isused to assess the implications of heat input in aluminium weld joints, identify the HAZ and its mechanical properties in the design of welding process parameters for automobile parts. The Welding parameters can be optimized to reduce the amount of heat input into the weld as this will directly affect the mechanical properties int he HAZ.