• A novel non-equilibrium partitioning model quantifies the influence of Mg and Si on hot cracking in SLM Al alloys, addressing the limitations of equilibrium partitioning models.
• The designed Al–7.5Mg–0.5Sc–0.3Zr–0.6Si alloy achieves a yield strength of 412 MPa and uniform elongation of 15.6%, demonstrating superior strength-ductility synergy.
• The alloy is crack-free under SLM, overcoming the trade-off between strength and hot cracking susceptibility.
• A tensile cracking model is proposed to explain the improved ductility, offering a design guideline for reliable aluminum parts via SLM.