Transverse crack formation in Al–Zn–Mg–Cu alloys during twin-roll casting: Effects of alloy composition and process parameters

The twin-roll casting (TRC) technique is associated with two simultaneously occurring sensitive processes, namely, solidification and deformation, making it difficult to ensure product quality. This study investigated the effects of alloy composition and process parameters on the formation of transverse cracks on a strip surface during the TRC of Al–Zn–Mg–Cu alloys, through both simulations and experiments. During TRC, transverse surface cracks are formed because of the presence of residual liquid phases along grain boundaries, which are susceptible to tearing under tensile stresses. Thermodynamic calculations were conducted to examine how variations in the contents of the major alloying elements affect the amount of residual liquid phase formed during the final stage of solidification. In addition, a thermal and mechanical analysis based on the finite element method was performed to investigate the effects of process parameters on the liquid fraction and tensile stresses on the strip surface during TRC. The results of both the thermodynamic and finite element analyses were experimentally validated through TRC trials under various alloy compositions. The findings provide valuable insights for minimizing the trial and error in the optimization of the TRC process for Al–Zn–Mg–Cu alloys.