Brilliant laser beam sources in connection with a high frequent beam oscillation make it now possible to join metallic material combinations, which have been conventionally non-laser weldable up to now. It concerns especially such combinations like Al-Cu, where brittle intermetallic phases occur. Extreme small weld seam with high aspect ratio leads to very short melt pool life time. These allow an extensive reduction of the heat input. On the other side the melting behavior at metallic mixed joint, seam geometry, chemical composition, melt pool turbulence and solidification behavior can be influenced by a high frequent time-, position-and power-controlled laser beam oscillation.