The solidification cracking susceptibility was calculated for quaternary Al-Si-Mg-Cu, Al-Zn-Mg-Cu and Al-Li-Mg-Cu alloy systems. It was calculated based on the crack susceptibility index |dT/d(f s ) 1/2 |, where T is temperature and f s the fraction solid. Three different levels of back diffusion were considered: no diffusion, diffusion under a cooling rate of 100 o C/s and diffusion under 20 o C/s. The calculated results were first validated by experimental data previously reported, and then extended to the composition ranges where no experimental data are available. For each alloy system, the crack susceptibility was calculated for 132651 Al alloys, with six crack susceptibility maps covering 15606 Al alloys at each diffusion level. These calculated results can be a database useful for welding, casting and additive manufacturing.

Solidification cracking can occur when neighbouring columnar grains are separated by tensile strain perpendicular to the grain boundary. In this study, a method to determine the tensile strain causing solidification cracking in welding was developed. A two-dimensional model was built to calculate the tensile strain perpendicular to the grain boundary during solidification, considering heat transfer, stress and strain evolution. The grain boundary direction was determined by calculating the temperature gradient and then the tensile strain causing solidification cracking was obtained by calculating the strain in the direction perpendicular to the grain boundary using strain transformation rule. This method to determine tensile strain causing solidification cracking can provide reference for future numerical and experimental studies on solidification cracking.

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An approach was developed to calculate the crack susceptibility under various levels of pressure, and the corresponding numerical method was presented. The binary Al-Si alloy system was selected for study because the effect of high pressure on its phase diagram has been reported. The results showed a higher pressure can lead to a higher crack susceptibility and shift the most crack susceptible composition to higher solute contents. It was found a higher pressure can increase the effect of back diffusion on the solidification path and hence the crack susceptibility. This study provides a new understanding of the effect of pressure on solidification cracking susceptibility and can be a relevant starting point for studying solidification cracking under high pressures.