Theoretical Prediction of Structural, Mechanical, and Thermophysical Properties of the Precipitates in 2xxx Series Aluminum Alloy

Abstract

We presented a theoretical study for the structural, mechanical, and thermophysical properties of the precipitates in 2xxx series aluminum alloy by applying the widely used density functional theory of Perdew-Burke-Ernzerhof (PBE). The results indicated that the most thermodynamically stable structure refers to the Al3Zr phase in regardless of its different polymorphs, while the formation enthalpy of Al5Cu2Mg8Si6 is only -0.02 eV (close to zero) indicating its metastable nature. The universal anisotropy index of AU follows the trend of: Al2Cu > Al2CuMg ≈ Al3Zr_D022 ≈ Al20Cu2Mn3 > Al3Fe ≈ Al6Mn > Al3Zr_D023 ≈ Al3Zr_L12 > Al7Cu2Fe > Al3Fe2Si. The thermal expansion coefficients (TECs) were calculated based on Quasi harmonic approximation (QHA); Al2CuMg shows the highest linear thermal expansion coefficient (LTEC), followed by Al3Fe, Al2Cu, Al3Zr_L12 and others, while Al3Zr_D022 is the lowest one. The calculated data of three Al3Zr polymorphs follow the order of L12 > D023 > D022, all of them show much lower LTEC than Al substance. For multi-phase aluminum alloys, when the expansion coefficient of the precipitates is quite different from the matrix, it may cause a relatively large internal stress, or even produce cracks under actual service conditions. Therefore, it is necessary to discuss the heat misfit degree during the material design. The discrepancy between a-Al and Al2CuMg is the smallest, which may decrease the heat misfit degree between them and improve the thermal shock resistant behaviors.