Abstract:Lightweight high-entropy alloys (LWHEAs) represent a promising class of materials for advanced structural applications. However, achieving precise control over their phase formation and mechanical properties remains a significant challenge. Although the conventional empirical parameters (mixing enthalpy ΔHmix, valence electron concentration, atomic size mismatch δ, and electronegativity difference Φ) provide general guidance for phase stability in Ti-Al-based LWHEAs, their predictive accuracy is restricted. The Al/Ti atomic ratio (γ, namely Al/Ti ratio) is a more decisive and precise criterion for microstructure control. Guided by this parameter, a series of Ti(50–x)Al(6.5+x)V11.5Nb14.5Zr17.5 alloys were designed and synthesized. Results reveal that γ critically governs the precipitation, extent of short-range ordering, and grain refinement of B2 phase. Additionally, a moderate γ value of approximately 2.0 (Ti46Al10.5 alloy) yields an optimal synergy of high yield strength (>1 GPa) and considerable tensile ductility (>20%), whereas excessively high γ leads to embrittlement. This work considers γ as a key compositional parameter and provides a practical framework for designing high-performance LWHEAs through integrated parametric and element-ratio control.