The Al-Zr (aluminum-zirconium) system

Investigating the Effect of Heat Treatment on the Microstructure and Hardness of Aluminum-Lithium Alloys

In this study, the effects of heat treatment on the microstructure and strength (micro-hardness) of an aluminum-lithium (Al-Li) base alloy containing copper (Cu) and scandium (Sc) were investigated, with a view to enhancing the alloy performance for aerospace applications. The heat treatment conditions were investigated to understand the precipitation behavior and the mechanisms involved in strengthening. Aging was carried out at temperatures of 130 °C and 150 °C for aging times of 1 h, 2.5 h, 5 h, 10 h, 15 h, 25 h, 35 h, and 45 h at each temperature for Al-Li alloy and at 160 °C, 180 °C, and 200 °C for aging times of 5 h, 10 h, 15 h, 20 h, 25 h, and 30 h at each temperature for Al-Li-Cu and Al-Li-Cu-Sc alloys. The investigation revealed that both solution heat treatment and artificial aging had a notable impact on strengthening the hardness of the alloy. This effect was attributed to the characteristics of the precipitates, including their type, size, number density, and distribution. The addition of copper (Cu) and scandium (Sc) was observed to have an impact on grain size refinement, while Cu addition specifically affected the precipitation behavior of the alloy. It led to remarkable changes in the number density, size, and distribution of T1 (Al2CuLi) and θ' (Al2Cu) phases. As a result, the hardness of the alloy was significantly improved after the addition of Cu and Sc, in comparison with the base Al-Li alloy. The best heat treatment process was determined as: 580 °C/1 h solution treatment +150 °C/45 h artificial aging for Al-Li alloy and 505 °C/5 h solution treatment +180 °C/20 h artificial aging for Al-Li-Cu and Al-Li-Cu-Sc alloys.

Effect of Cu Content on the Alloy Tensile Properties of Al-Cu Based Alloys Tested at 25 °C and 250 °C: Application of the Concept of Quality Index

The present work was performed on three versions of a newly developed alloy coded T200 containing 6.5% Cu, 0.1% Fe, 0.45% Mg, and 0.18% Zr in addition to A319 and A356 alloys (grain refined and Sr-modified). Tensile bars were subjected to 13 different heat treatments prior to testing at either 25 °C or 250 °C. The tensile data were analyzed using the quality index method. The results obtained showed that, due to the high copper content in the T200 alloy coupled with proper grain refining, the alloy possesses the highest quality as well as improved resistance to softening when tested at 250 °C among the five alloys. The results also demonstrate the best heat treatment condition to maximize the use of the T200 alloy for automotive applications. Grain-refined alloy B, treated in the T6 temper and tested at 250 °C, exhibited the best combination of the four tensile parameters, i.e., UTS, YS, %El, and Q-values: 308 MPa, 304 MPa, 2.3%, and 352 MPa, respectively, which are comparable with those obtained from the 356 alloy: 309 MPa, 305 MPa, 2.8%, and 375 MPa in the same order.

Laser Directed Energy Deposition of an AlMgScZr-Alloy in High-Speed Process Regimes

Aluminum-magnesium-scandium-zirconium (AlMgScZr) alloys need to be rapidly cooled from the liquid state to obtain a high degree of solute supersaturation that helps to exploit the precipitation hardening potential of the material. While AlMgScZr alloys have been successfully used in laser powder bed fusion (LPBF) processes, there has been little research in the field of laser directed energy deposition (DED) of the material. The limited previous studies have shown that the performance of AlMgScZr parts fabricated with DED only reached about 60% of that of the parts fabricated with LPBF. In view of breaking through the limitation associated with the process conditions of conventional DED, this work demonstrates the DED of AlMgScZr alloys in high-speed process regimes and elucidates the mechanism of enhancing the hardness and tensile strength of AlMgScZr alloys by increasing the cooling rate by one to two orders of magnitudes, as well as reducing the track overlapping and the porosity of the specimens during the process. A maximum average hardness of nearly 150 HV0.1 and a max. tensile strength of 407 MPa are obtained by using an energy per unit length of 5400 J/m and a powder feed rate per unit length of 0.25 g/m.

Intermetallic Growth and Interfacial Properties of the Grain Refiners in Al Alloys

Al₃TM(TM = Ti, Zr, Hf, Sc) particles acting as effective grain refiners for Al alloys have been receiving extensive attention these days. In order to judge their nucleation behaviors, first-principles calculations are used to investigate their intermetallic and interfacial properties. Based on energy analysis, Al₃Zr and Al₃Sc are more suitable for use as grain refiners than the other two intermetallic compounds. Interfacial properties show that Al/Al₃TM(TM = Ti, Zr, Hf, Sc) interfaces in I-ter interfacial mode exhibit better interface wetting effects due to larger Griffith rupture work and a smaller interface energy. Among these, Al/Al₃Sc achieves the lowest interfacial energy, which shows that Sc atoms should get priority for occupying interfacial sites. Additionally, Sc-doped Al/Al₃(Zr, Sc) interfacial properties show that Sc can effectively improve the Al/Al₃(Zr, Sc) binding strength with the Al matrix. By combining the characteristics of interfaces with the properties of intermetallics, the core-shell structure with Al₃Zr-core or Al₃Zr(Sc1-1)-core encircled with an Sc-rich shell forms.

Quantum chemical calculations of thermodynamic and mechanical properties of the intermetallic phases in copper–scandium alloy

To understand how the intermetallic phases of Cu–Sc influence the thermal stability and mechanical strength of Cu–Sc alloys, thermodynamic and mechanical characters of the Cu–Sc alloy have been calculated by first-principles. The lattice parameters of Cu4Sc phase are obtained by calculated and the CuSc phase is found to be the most stable phase based on formation energies. In the binary Cu–Sc alloy, the shear moduli of Cu4Sc and Cu2Sc phases along the [100](001) crystal orientation are easier than those along the [100](010) crystal orientation, respectively. Pure Cu phase acts as the most stiffness phase while [Formula: see text]Sc phase has the lowest stiffness. Cu4Sc phase possesses the best plasticity while CuSc phase possesses the worst plasticity. Cu4Sc phase is the most ductile phase while [Formula: see text]Sc phase is the most brittle phase. From the partial density of states, the valence bands of binary Cu–Sc phases are dominated by the Sc-[Formula: see text] states.

Measuring Enthalpies of Formation Using Thick Multilayer Foils and Differential Scanning Calorimetry

The exothermic, solid state reaction of Al and Zr has been studied in thick AL/Zr multilayers using Differential Scanning Calorimetry and X-ray diffraction. The multilayersamples were magnetron sputter deposited into highly textured alternate layers of Al and Zr with nominal composition A13Zr. The samples used in this study were 47μm thick with a 427Å period. When samples were isochronally scanned from 25º to 725ºC, a large exotherm at ˜350ºC was followed by one or two smaller exotherms at ˜650ºC. The first exotherm is dominated by a diffusionbased reaction of Al and Zr that produces two phases in isochronal scans: amorphous AI-Zrand cubic A13Zr, and two additional phases in isothermal anneals: A12Zr and tetragonal AI3Zr. The exothermic heat from this multi-phase reaction is measured using isochronal scans and isothermal anneals, and the heat flow is analyzed using a l-D diffusion based model. An average activation energy and a diffusion constant are determined. In the isothermal scans, the total exothermic heat increases linearly with √ime, and layer thicknesses vary linearly with heat.

FLAPW: applications and implementations

Modern material design involves a close collaboration between experimental and computational materials scientists. To be useful, the theory must be able to accurately predict the stability and properties of new materials, describe the physics of the experiments, and be applicable to new and complex structures-the all-electron full-potential linearized augmented plane wave (FLAPW) is one such method that provides the requisite level of numerical accuracy, albeit at the cost of complexity. Technical aspects and modifications related to the choice of basis functions (energy parameters, core-valence orthogonality, extended local orbitals) that affect the applicability and accuracy of the method are described, as well as an approach for obtaining k-independent matrix elements. The inclusion of external electric fields is illustrated by results for the induced densities at the surfaces of both magnetic and non-magnetic metals, and the relationship to image planes and to nonlinear effects such as second harmonic generation. The magnetic coupling of core hole excitations in Fe, the calculation of intrinsic defect formation energies, the concentration-dependent chemical potentials, entropic contributions, and the relative phase stability of Zr-rich Zr-Al alloys are also discussed.