The metal inert gas (MIG) welding and the crucial parameters influenced on the thermal and mechanical behaviours, and microstructure of AA 6063 aluminum were investigated through the experiment and the FE simulation. A thermo-mechanical model was extended using the finite element software of ABAQUS. In this manner, the thermal distribution and time-temperature histories made during MIG welding were derived. To achieve more accuracy, a subroutine was developed by FORTRAN. The real-time temperature measurements and the effective parameters of the thermal distribution, including the welding speed and the arc voltage were studied by conducting MIG bead-on-plate welds and the residual stresses derived from the simulation were compared with the empirical observations. The results depicted that the simulation would estimate rigorously the temperature gradients and the fields of welding-induced stress. The microstructural and microhardness examinations were also conducted which allowed - alongside the TTT curve - the phases precipitated and the heat sink effects were studied and foreseen. Indeed, the microstructure images demonstrated that the overaged, agglomerated β-Mg2Si phases, in the HAZ, and the modified β-AlFeSi pseudo-platelike precipitates alongside the smaller and coarsened β-Mg2Si phases, in the fusion zone, were precipitated.