Susceptibility of ternary aluminum alloys to cracking during solidification

The crack susceptibility map of a ternary alloy system indicates the composition range most susceptible to cracking, which should be avoided in welding or casting. The crack susceptibility maps of ternary Al alloy systems Al-Mg-Si, Al-Cu-Mg and Al-Cu-Si were calculated based on the maximum |dT/d(fS)1/2| as an index for the crack susceptibility, where T is temperature and fS fraction solid. Three levels of back diffusion were considered: no back diffusion, back diffusion under a 100 °C/s cooling rate, and back diffusion under 20° C/s. The location of the region of high crack susceptibility, which is the most important part of a map, was shown. These locations were compared with those observed in crack susceptibility tests by previous investigators. With back diffusion considered, either under 20 or 100 °C/s, the agreement between the calculated and observed maps was good especially for Al-Mg-Si and Al-Cu-Mg. Crack susceptibility maps of Al-Cu-Mg: (a) calculated with diffusion under 20 °C/s cooling rate; (b) measured.339