Because aluminum has a lighter weight and higher strength than iron, it is frequently used in the transportation industry for the purpose of reducing the weight of a chassis, and thereby increasing fuel efficiency. However, there are some difficulties with arc welding aluminum due to its lower melting point, high thermal conductivity and oxidation coating on its surface. This study proposed using superposition ac pulse MIG arc welding, which has been improved from the pulse waveform of conventional MIG welding. A MIG arc welding power source was developed to test the effectiveness of this method.