The tensile mechanical response of three semi-solid as-cast aluminum alloys - AA3104, AA6111, and CA31218 (an alloy similar in composition to AA3003) - was measured between a fraction solid f(s) similar to 0.85 and f(s) similar to 1 in order to establish the mushy zone constitutive behavior under conditions similar to those believed to occur during direct chill (DC) casting. The fraction solid vs. temperature relationship for these alloys is also provided. The constitutive behavior appears greatly dependent on both fraction solid and strain rate. Furthermore, while the behavior is dominated by the solid network, the critical fraction solid for complete loss of ductility was found to be alloy dependent, ranging from f(s) similar to 0.94 for CA31218 to f(s) similar to 0.99 for AA61111. The variation in both ductility and stress with temperature has been used to propose a brittle temperature range for each of the three alloys and to rank their hot tearing susceptibility. (C) 2008 Elsevier B.V. All rights reserved