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At room temperature, Al alloys have excellent mechanical properties and are widely used in automotive, electronics, aerospace and other fields, but it is difficult to maintain this advantage in the middle and high temperature ranges. To address this issue, second-phase Al11RE3 (RE represents rare earth element) was introduced into a Al-Mg-RE alloy as its primary constituent. By incorporating RE elements as additives, this material exhibits exceptional mechanical and thermal properties at elevated temperatures. Based on first principles and quasi-harmonic approximation (QHA), the nucleation growth mechanism and surface properties of second-phase Al11RE3 were studied in this paper. The interfacial energy γ α / β , strain energy Δ E CS and chemical driving force Δ G V of Al11RE3 were obtained. Models1, 4, and 6 have better properties of para-site connections than inter-site connections. It is found that the resistances of particle nucleation, interface energy γ α / β and strain energy Δ E CS , first increase and then decrease with increased atomic number REs, but they are much smaller than the chemical driving force Δ G V . A reduced chemical driving force and a diminished nucleation radius R* are more favorable for the process of nucleation. The addition of Sc is the most unfavorable for nucleation, and La has the strongest nucleating ability, which gradually decreases as the atomic number of the lanthanide element increases. The nucleation ability of the Al11RE3 phase decreases with increasing temperature, which is consistent with the experiments. The nucleation radius R* also increases with increasing temperature, indicating that the nucleation ability decreases as the atomic number of the lanthanide elements increases. Since the smaller the nucleation radius R* the easier the nucleation, compared with model4 and 6, model1 has a smaller nucleation radius R* and the smallest increment. Thus, model1 is more prominent in the nucleation mechanism. In the particle growth study, the smaller the diffusion activation energy Q, the faster the diffusion rate in the Al matrix, and hence the higher the coiling rate, which promotes the growth of second-phase particles. The diffusion activation energy Q decreases sequentially from La to Ce and then increases with atomic number. The coarsening rate K LSW of the Al11RE3 phase in models1, 4, and 6 increased with increasing temperature, which promoted the growth of particles. This paper is intended to provide a solid theoretical basis for the production and application of aluminum alloy at high temperatures. [ABSTRACT FROM AUTHOR]

Based on first-principles calculations, the effects of substitutional defects of the 3d–5d transition metal elements TMAl on the stability and thermal conductivity of the aluminum matrix were investigated. The results show that with an increase in the atomic number of TM, the defect-forming energy Ef of TMAl exhibits a periodic change feature, which depends on the valence electron configuration of the TM elements. The thermodynamic property parameters calculated with the Debye theory show that the addition of TM atoms does not change the stability of an Al system and can effectively reduce the thermal expansion coefficient of the material. But the equilibrium lattice constant a0 of Al-TMAl supercells changes very little. As the temperature increases, the relaxation time τ decreases, and both the electronic thermal conductivity κe and the total thermal conductivity κ decrease at the temperature range of 100–200 K, followed by a small increase or decrease. Because the lattice thermal conductivity κl is very small in the whole temperature range, the changes in electronic thermal conductivity and total thermal conductivity are basically the same. Moreover, when 1 at.% TM was added at both 300 K and 600 K, it was found that the influence of TM solute atoms on the thermal conductivity κ of Al was much greater than that of the second-phase particles. For solid solution atoms, Pd and Pt atoms have the greatest influence on the thermal conductivity of pure Al. This work is helpful for designing high-performance, heat-resistant Al-based alloys. [ABSTRACT FROM AUTHOR]

The interface structure and segregation behavior of L12-Al3M (M = Sc, Zr, Er, Y) phases were investigated based on first-principles calculations. The results showed that the order of the thermodynamically stable interface was Al3Zr/Al > Al3Sc/Al > Al3Er/ Al > Al3Y/Al. The interfaces of Al3Sc/Al3Zr, Al3Er/Al3Zr, and Al3Y/Al3Er obtained negative interfacial energies and low coherent strain energies and were favorable to form a clear interface. Zr atom tended to segregate to the first atomic layer on the Al side of the Al/Al3Sc, Al/Al3Er, and Al/Al3Y interfaces. The driving effect of the Zr atom segregation to the Al3Y shows was stronger than that to Sc and Er atoms, whereas the high coherent strain energy hindered the formation of Al3Y/Al3Zr interface. Er atom tended to segregate at the Al/Al3Y interface and accelerated the formation of core-shelled Al3Y/Al3Er. Furthermore, the formation of the double core-shelled Al3Y/Al3Er/Al3Zr was discussed. [ABSTRACT FROM AUTHOR]

The stability and mechanical and thermodynamic properties of Al11RE3 intermetallics (RE = Sc, Y and lanthanide La-Lu) have been investigated by combining first-principles and Debye model calculations. It was found that the formation enthalpies of the Al11RE3 intermetallics are all negative, indicating that they are stable; moreover, the experimental values of Al11La3 and Al11Ce3 are in good agreement with the predicted values, which are −0.40 kJ/mol and −0.38 kJ/mol, respectively. The calculated results of the mechanical properties reveal that the Young's modulus E and shear modulus G of Al11RE3 (RE = La, Ce, Pr, Nd and Sm) intermetallics are obviously greater than that of Al, implying that the stiffness, toughness, and tensile strength of them are significantly greater than those of aluminum, and that they, as strengthen phases, can effectively improve the mechanical property of aluminum alloys. The Poisson's ratio v of Al11Sc3 (0.37) is the largest, and the heterogeneity is obvious. All the Al11RE3 intermetallics can enhance the thermostability of the aluminum because of their lower Gibbs free energy F in the range of −5.002~−4.137 eV/atom and thermal expansion coefficient α of Al in the range of 2.34~2.89 × 10−5/K at 300K, as well as higher entropy and constant volume-specific heat than aluminum at finite temperatures. With an increase in the atomic number, different change trends were observed for the formation enthalpy ΔHf, bulk modulus B, Young's modulus E, and shear modulus G. This paper can provide ideas and help for designing a high-performance, heat-resistant aluminum alloy. [ABSTRACT FROM AUTHOR]

Abstract Experimental measurement of surface energy is rather difficult at finite temperature. This work develops a first-principles method to estimate the effects of finite temperature on the surface energy of Al alloys. The surface energies of four planes, namely, (100), (110), (111) and (112) planes, have been calculated as a function of the finite temperature, as well as the interaction energies between the solute atoms and these surfaces. The uniform distribution (UFD) model is used to treat the distributions of solute atoms in investigating the microcrack nucleation mechanism. The results suggest that the four surface energies of pure Al decrease slightly with increasing the temperature. While Sn atom can drastically reduce the four surface energies of Al alloys at relatively high solute concentration, which obviously increases the probability of forming a new surface, inducing more microcracks in Al alloys. Interestingly, Cu atom can inhibit the microcrack nucleation of (100) and (111) surfaces by slightly increasing their surface energies. Microcracks in Al alloys prefer to nucleate along the (111) surface due to the lower surface energy. This work provides a valuable insight for further exploring the surface characteristics of Al alloys at finite temperature. Highlights • Effects of finite temperature on the surface energy of Al alloys are investigated by first-principles calculations. • Results indicate that finite temperature has a small impact on the surface energy. • Sn atom can obviously increase the probability of the microcrack nucleation. • Cu atom can inhibit the microcrack nucleation of (100) and (111) surfaces. [ABSTRACT FROM AUTHOR]

The mechanical, thermal and electrical properties of 8 types of common Al x TM y (TM = Sc–Zn, Y–Cd, Hf–Hg) intermetallics in Al based alloys at various temperatures and pressures have been investigated by combining first-principles calculations with the Debye model. The results clearly show that the stability and mechanical property are closely related to the types of configurations and TM elements. The electronic structure for AlRh and AlCd alloys are used to study the characteristics of stable compounds, and it is found that more transferred electrons will make the lattice mismatch δ larger. The Cauchy pressure C 12 – C 44 and electric local function (ELF) present underlying characteristics of bonds and physical mechanisms. Further, the Helmholtz free energies F of both Al bulk and stable Al x TM y intermetallics are decreased with increasing temperature, while the entropy S , heat capacity C V and coefficient of expansion a T show the opposite trends. And the smaller F leads to the lower a T ; that is the compounds constitute of elements of IB ∼ IVB have larger F and a T , while the compounds with VB ∼ VIIB possess smaller F and a T. In short, all calculated parameters in this work show the same change with the atomic number in for three periods 3-5d, indicating that the structure of the TM valence electron layers are the main reason for the underlying mechanisms. This work is helpful for the study of high-performance of structural Al-based alloys. • The ΔHf is closely related to the types of crystal configurations and TM elements, and so is the mechanical properties. • The δ of more than 60 % of precipitates is larger than 4 %. And the δ of all structures first decreases, and then increases in the same cycle with the increase of atomic number, except for AlTM2 and Al11TM3. Clearly, more transferred electrons will make the δ larger. • The B, G and E of most Al-TM compounds are improved, except for D022-Al3Hg, the B of B2–AlY, L12-Al3(Zn, Y), D019-Al3Y, Al(Sc, Y)2 and Al11Y3, and the E of AlY2. The Cauchy pressure of C12–C44 demonstrate only ∼23 % of the compounds show directional covalent characteristic, and the compounds with d5-8 shells show stronger metallic characteristic. • About 5.31 % of the stable compounds present uniform deformation, and 26.55 % of the stable intermetallic particles show brittleness; the B/G and ν of 31.86 % compounds are larger than that of Al. The valence electron configurations directly decide ν and B/G of AlxTMy, the same as B, G and E moduli. • The Helmholtz free energy F of all stable Al-TM compounds including Al bulk is slightly decreased with increasing temperature. With the increase of temperature, the increasing velocity of entropy S continuously slowed down; and the constant volume heat capacity CV of compounds increase drastically at 0–300 K, and nearly unchanged elevated temperatures. The aT of all Al-TM compounds including Al increases fast and nearly linearly at 0–300 K, and increases exponentially after 600 K. [ABSTRACT FROM AUTHOR]