Effects of Si, Fe, Mn and Mg on Solidification Characteristics of EN-AW 3105 Alu-minum Alloy: A CALPHAD-Based Multi-Objective Optimization

Centerline segregation driven by the mushy zone width remains the primary defect limiting the broader application of twin-roll casting (TRC) for 3xxx series aluminum alloys. In this study, the individual and combined effects of Si (0.10–0.50 wt.%), Fe (0.30–0.70 wt.%), Mn (0.30–0.70 wt.%), and Mg (0.20–0.60 wt.%) on the solidification range, liquidus and solidus temperatures, and latent heat of fusion of EN-AW 3105 alloy were investigated using 56 equilibrium calculations performed with ThermoCalc. Sobol variance-based global sensitivity analysis revealed that the solidification range is predominantly controlled by Mn (total-order index ST = 0.512), attributed to the high equilibrium partition coefficient of Mn in aluminum (k₀ ≈ 0.94) and the promotion of Al₆(Fe,Mn) intermetallics that raise the solidus temperature. Si overwhelmingly governed the latent heat (ST = 0.926) through its control over the Al-Si eutectic fraction, while Si and Mg co-dominated the liquidus temperature (ST = 0.445 and 0.345, respectively). Fe showed consistently low thermophysical sensitivity (ST < 0.16), confirming its primary role in controlling intermetallic morphology rather than solidification temperatures. To identify optimal compositions for TRC, a Gaussian Process Regression surrogate model (10-fold CV R² = 0.90, selected from five candidate algorithms) was coupled with the NSGA-III evolutionary algorithm for simultaneous minimization of solidification range, liquidus temperature, and latent heat. Entropy-weighted TOPSIS identified a compromise composition of Si: 0.38, Fe: 0.70, Mn: 0.70, Mg: 0.24 (wt.%) with a solidification range of 7.24 °C (8.9% improvement), whose Mn/Fe ratio (≈1.0) additionally promotes the beneficial β→α intermetallic transformation.