Hot tearing and loss of dimensional stability are two key defects related to industrial aluminum alloy casting processes. In order to investigate their occurrence, a new semi-solid constitutive law [20] for AA5182 that takes into account cooling rate, grain size and porosity has been implemented into a Direct Chill casting process model for round billets. The semi-solid stressstrain predictions provided by this new constitutive law as well as the effects of processing parameters were then examined to demonstrate the relationships between defect formation, microstructure, and processing variables.