This paper provides an analysis of a co-extrusion process. The compound consists of the sleeve material, aluminum, and the core material, magnesium. It is imperative to produce impeccable compounds without cracks in the interface. Therefore, a simple indicating value for damaging effects during the process is necessary. In the numerical simulation the compound quality is noticeable by the current macro mechanical criterion of axial strain difference. A statistical analysis verifies this criterion as an adequate quality criterion. By means of this criterion it is possible to define a stable process window for the co-extrusion process.