To predict hot tearing of direct chill casting ingot, both the tensile constitutive behavior and elongation of alloy are inevitable during partial solidification. For predicting both the maximum true stress σss and the elongation εelong regardless of alloy systems, their dominant factor was examined in terms of the solidification microstructure. For an Al–Mg and an Al–Cu alloys, (i) temperature T dependences of the maximum true stress and elongation (σss=f(T) and εelong=f(T)) and (ii) dihedral angle θ of liquid phase formed at grain boundary were measured experimentally. Then, fraction of solid cohesion C was determined by the Campbell’s model using the angle. Firstly, the solid fraction dependence of the tensile properties (σss=f(fs) and εelong=f(fs)) were compared between the two alloys. The two dependences differ with each other. Secondly, the fraction of solid cohesion dependences of the tensile properties (σss=f(C) and εelong=f(C)) were compared and the result shows that the two dependences were consistent with each other. The fraction of solid cohesion enables to explain the difference in solid fraction dependence of the tensile properties for the two alloys. The result demonstrates that the dihedral angle should be essential to predict the two tensile properties of alloy during partial solidification.