Investigating hot tearing in 6xxx-series aluminium alloys: A combined thermodynamic and experimental approach

The hot tearing of 6xxx-series aluminium alloys has been investigated over four levels of silicon (0.6, 0.8, 1.0, 1.2 wt%), magnesium (0.4, 0.6, 0.8, 1.0 wt%), iron (0.2, 0.4, 0.6, 0.8 wt%) and manganese (0.0, 0.2, 0.4, 0.6 wt%). Thermodynamic calculations based on the CALPHAD method were performed to evaluate the hot tearing index using the Kou criterion, and the results were compared with experimental data obtained by thermal analysis and microstructural investigations. The results revealed that the concentration of alloying elements, particularly silicon and magnesium, significantly affects the Kou index and the hot tearing behaviour of the material. An increase in iron content and the addition of manganese showed a beneficial effect on the resistance to hot tearing. The formation of branched α-AlFeSiMn compounds significantly reduced the development of hot tearing cracks, more so than the increased presence of the Mg 2 Si phase. Comparison of Kou index values derived from both thermodynamic calculations and experimental solidification curves showed that the selection of the solid fraction range is crucial. Good agreement was achieved between the calculations and the experimental data when using a solid fraction interval of 0.87–0.94. Finally, the experimental results confirmed that a preliminary qualitative assessment of susceptibility to hot tearing can be made without resorting to more resource-intensive testing methods. • Initial levels of Si and Mg significantly affect the hot tearing behaviour of AlMgSi alloys • Fe and Mn show beneficial effect on the resistance to hot tearing • Branched α-AlFeSiMn compounds reduce hot tearing cracks • Kou index must be calculated in the 0.87–0.94 fraction solid range