Crack susceptibility of binary aluminum alloys during solidification

Cracking can occur during solidification in welding and casting. It has been proposed and verified recently that the maximum steepness |dT/d(fS)1/2| of the curve of temperature T vs. the square root of fraction solid fS, can be used as the crack susceptibility index. The present study showed that variable equilibrium segregation coefficient k and back diffusion can both be considered in calculating the index. Al alloys were studied over a wide range of the eutectic temperature TE (229-548 °C) and k (about 0-0.87 at TE), such as Al-Cu, Al-Mg, Al-Zn and Al-Sn. It was shown that with a large k back diffusion can significantly reduce the crack susceptibility even when the freeing temperature range is very wide due to a very low TE. This is consistent with the better crack resistance of Al-Mg and even Al-Zn than Al-Cu, which has a much narrower freezing temperature range. The effect of the curvature of the liquidus and solidus lines on the crack susceptibility was shown. A possible link between the dihedral angle and bridging between grains was also shown.248