Effect of diffusion on susceptibility to cracking during solidification

Cracking during solidification is a serious defect in welds and castings. This study showed that increasing solute (e.g., Cu) diffusion into Al-rich dendrites (i.e., increasing the diffusion parameter α′) can significantly reduce the peak of the crack susceptibility and shift it to higher solute contents. Differences in diffusion due to differences in the cooling rate during welding or casting may contribute to the wide scatter in the reported peak positions (indicated by arrows). This study also showed that diffusion is unusually high in Al-Mg alloys due to the very high (17.5 wt%) Mg solubility in solid Al, which explains their low crack susceptibility despite their very wide freezing temperature range.128