This paper renders research into the fundamentals governing the melt pool dynamics of a hybrid bifocal laser welding system consisting of an Nd:YAG and a high power diode laser (HPDL). The resulting superposition of keyhole by heat conduction mode welding is assayed for extruded aluminum. In particular the diffusion of the surface oxygen layer is considered. By comparing the results attainable by bifocal laser hybrid welding to the constituent laser processes synergetic effects of the laser hybrid can be demonstrated. These are namely the doubling of the welding speed from 2.0 min-1 to 4.0 m min-1, the reduction of the roughness of the weld surface from 60 om to approximately 10 om and an increase in energy transfer efficiency. The experimental investigations verifying these synergies are outlined and discussed.