Modelling represents an important tool in modern material processing which no longer follows the traditional trial and error route but rather represents what may be termed a right first time technology [1]. To successfully model technological solidification processes, thermodynamic and kinetic data are required. But mechanical aspects are important as well [2]: during solidification, temperature gradients or mechanical constraints imposed by the mold result in solidification stresses. These stresses must be considered for at least the following two reasons: first, they can lead to local air gap formation between metal and mold thus changing heat extraction, cooling rate and finally the cast microstructure [3]; second, at a larger scale they may influence the final product shape [4]. Moreover, they can assist in cavity formation and can produce cracking. Such stresses become important as soon as a significant amount of solid phase has formed during solidification. In principle, these stresses can be calculated using viscoelastic finite element stress analysis [5]. But, finite element calculations require as an input the constitutive law which governs the mechanical behavior. Therefore, there is an interest in mechanical data of solidifying alloys with mushy zone microstructures: Ackermann and Kurz [6] investigated the mechanical properties of a solidifying AIMg alloy perpendicular to the growth axis of the columnar crystals. The tensile behavior of solidifying AI-Cu alloys was studied by Wisniewski [7] and recently, Branswyck [8] proposed a modified indentation test which, in combination with FEM analysis, yields quantitative flow rules. Nevertheless, there is still a need for more mechanical data of solidifying alloys, especially creep data - where strain accumulates at a constant stress - only rarely exist for processing conditions.