In this thesis the characteristic properties of natural aging AlZnMg(Cu)-cast alloys such as hot cracking susceptibility and corrosion resistance, particularly stress corrosion cracking (SCC) were studied. The aim of this work was to optimize an alloy for shape casting, which exhibits good castability and low hot cracking tendency, good mechanical properties and low stress corrosion cracking. Furthermore these properties should be obtained without an energy-intensive heat treatment such as T6 or T7 treatment involving solution annealing. The conflicting properties were addressed by improved grain refinement and intermetallic phase selection in the last stages of solidification. The thermodynamic calculation of the phase selection was performed with the program ThermoCalcClassic (TCC) to predict the influence of chemical composition on the grain growth restriction factor (Q-factor) for grain refinement, precipitated phases during phase selection and their constitution, which is essential to elucidate hot cracking, stress corrosion cracking and their mechanical properties. A dog bone shaped mould was used to determinate the hot cracking susceptibility of different alloys. Theoretical models including the cracking susceptibility coefficient (CSC) by Clyne and Davies were considered. Thermodynamic calculations of the behaviour of the fraction solid during solidification in particular the terminal freezing range (TFR) and eutectic fraction were compared to the experimental hot cracking indexing (HCI) method. Different corrosion tests such as constant load tests and potentiodynamic polarization curves were conducted to determine the influence of the chemical composition and different heat treatment conditions on the stress corrosion cracking behaviour of AlZnMg(Cu)-Cast alloys. The influence of elements such as Mg, Cu and Sc on the hot cracking, stress corrosion cracking and grain refinement were investigated. The determined properties correlate well between the theoretical calculations by TCC and the by electron microscopy detected phases. For an alloy showing decreased hot cracking tendency an optimized heat treatment, which increases the stress corrosion cracking resistance in AlZnMg(Cu)-Cast alloys, was found using a combination of differential scanning calorimetry (DSC) and TCC simulations.