A three-dimensional computational model of metal–inert-gas welding of aluminium has been developed. The model includes the arc and both electrodes self-consistently. Here, the model is used to investigate two phenomena. First, the influence of the metal vapour that is produced from the electrodes on the arc and the weld pool is considered. Second, the mixing of droplets formed from the upper wire electrode with the weld pool is examined. The predicted weld pool shape is compared with measurements.