Cellular metallic materials are considered as an innovative material solution in the fields of light-weight structures, energy absorption or silencing. One of the most important requirement to find new applications for cellular metals is to integrate them in complex technical structures. The foams have to be joined to each other or to sheet materials by means of suitable joining techniques. Ultrasonic welding of similar materials such as metals or plastics is established in industrial production sequences since a long time, e. g. for bonding cable bundles, solarpanels and video cassettes. To enlarge the ultrasonic welding technique one research field of the Institute of Materials Science is the systematic investigation of the ultrasonic welding capability of joints between different material combinations such as metal foams to sheet material. In the ultrasonic welding system an ultrasonic generator, a converter and a booster convert the main voltage into high frequency mechanical oscillations. The actual bonding of the joining partners takes place through the transfer of this high frequency shear oscillation via the connecting surface of the welding tool into the sheet material. At the same time a static pressure, perpendicular to the oscillation direction, is brought up. By different configurations of the machine components and a suited welding tool different welding seams can be realized: Spot, line or circular seams. The ultrasonic welding technique allows to join cellular metallic materials to sheet metals. Different aluminum- and steel-alloys are used as sheet material. Foams of different aluminum alloys are part of the investigations. Successful welding experiments were performed with foams made from powder as well as foams made from melts. Aim of the investigations is to optimize the welding parameters to achieve maximum joint strength. The joints are tested under tensile shear load and tensile load. To get information about the mechanisms in the bonding zone additional metallographic, thermometric and microscopic investigations were carried out. In comparison to other joining techniques, ultrasonic welding is characterized by low energy input, short welding times (< 3 s) as well as relatively low welding temperatures (< 500 °C). This technique allows to join aluminum foams with sheet material without producing significant damages or deformations in the joining partners. Further advantages are the easy automation and the very high environmental compatibility. At the time tensile shear strength up to 40 MPa can be reached by ultrasonic welding of aluminum foams to sheet material.