Dihedral Angle and Cracking During Solidification

Cracking can occur along the grain boundary during solidification in welding, casting and additive manufacturing of alloys. In cracking susceptibility models the calculated cracking susceptibility can be significantly affected by the value of f_SB, which is the fraction of solid f_S beyond which cracking can no longer occur because of extensive bonding along the grain boundary. Unfortunately, the value of f_SB needs to be specified arbitrarily. The present study showed a way to calculate f_SB from the dihedral angle 2θ. For the purpose of illustration, a simple index for the cracking susceptibility was used, i.e., the maximum |dT/d(f_S)^1/2| up to f_SB (where T is temperature). Selected Al–Cu and Al–Mg alloys were analyzed, whose cracking susceptibility was tested and whose dihedral angles were measured after testing. For each alloy, the curve of T vs. (f_S)^1/2 was calculated based on its composition, and f_SB based on the measured dihedral angle. The calculated index and the measured cracking susceptibility were compared.