Influence of impurity elements on the castability of recycled 6xxx series Al alloys

Hot tearing represents a relevant limitation to castability, particularly in wrought aluminum alloys having a wide solidification range. To assess the alloy’s vulnerability to hot tearing, a variety of predictive models and testing methodologies have been developed. This study aims to validate the Kou model through the comparison of experimental data obtained using the Constrained Rod Casting (CRC) test on selected 6XXX series Al alloys. Additionally, the investigations explore the influence of microstructural features and phase constituents on the formation of hot tears. The results indicate that the sensitivity to hot tears is higher in alloys with 0.2 wt% Fe and decreases by increasing iron content. The α-Al15(Fe,Mn)3Si2 phase appears to promote grain coalescence, facilitating bridging between primary dendrites and, thereby, improving the castability of the alloy. Furthermore, the study suggests that thermodynamic simulation and the application of Kou index can offer valuable insights into the casting of alloys. These findings will contribute to the identification of optimized alloy chemistries suitable for producing near-net-shape components using casting techniques traditionally applied to Al casting.