Al/Mg compounds produced by hydrostatic extrusion exhibit unique characteristics in terms of high strength and low weight, which are required in lightweight safety parts. The compound interface between the core and sleeve is a brittle intermetallic phase consisting of Al 2 Mg 3 and Al 12 Mg 17 . However, a certain plastic deformability is required for subsequent processing of the semi-finished product by forming. To obtain a basic understanding of the deformation behaviour of the interface, the Digital Image Correlation is used together with a new analysis procedure based on the approximation of the displacement field with polynomial functions. The procedure is first tested with a bending test. The specimens exhibit a remarkable deformation behaviour under bending at high temperatures, which is confirmed by the results of radial upsetting tests. Even under a multi-axle load, the interface maintains a full material joint, though fragmentation occurs, and a new secondary interface between the fragments can be observed. In addition, an evaluation of light microscopy images and Eulerian Hencky strain values at the interface, which are based on the Digital Image Correlation results, imply a connection between the strain and the boundary layer's appearance.