Prediction and quantitative study on the dimensional evolution of Al-Cu-Mg alloy with single-precipitate phase during isothermal aging

As aluminum alloys are widely employed in the fabrication of precision instruments, their dimensional changes can adversely affect the accuracy and reliability of the final products. In this study, a predictive model was developed to quantitatively estimate the macroscopic dimensional change rate of an Al-Cu-Mg alloy containing a single precipitate phase during the aging process. An alloy composition of Al-4.33Cu-1.74 Mg wt% was designed through thermodynamic calculations, revealing that matrix lattice contraction and S phase precipitation are the dominant contributors to dimensional change rates. Microstructural characterization further demonstrated a deviation in the atomic ratio of Mg to Cu within the S II phase, with a measured Mg: Cu ratio of 1.38:1 in the S II phase after 24 h of aging. Incorporating these findings, a quantitative model was established by combining the calculated volume fraction of the S phase and lattice constant variation obtained from thermodynamic analysis. Upon introducing a kinetic correction factor, the predicted dimensional change rates exhibited excellent agreement with experimental measurements (e.g., −5.71 × 10⁻⁵ vs. −4.57 × 10⁻⁵ at 48 h). This work offers a comprehensive approach for accurately predicting the dimensional stability of Al-Cu-Mg alloys, providing valuable insights for alloy design and precision component fabrication.