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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on MgZn by Materials Project

MgZn crystallizes in the orthorhombic Amm2 space group. The structure is three-dimensional. there are three inequivalent Mg sites. In the first Mg site, Mg is bonded to four Mg and eight Zn atoms to form distorted MgMg4Zn8 cuboctahedra that share corners with six equivalent MgMg4Zn8 cuboctahedra, corners with twelve ZnMg8Zn4 cuboctahedra, edges with six ZnMg8Zn4 cuboctahedra, edges with eight equivalent MgMg2Zn8 cuboctahedra, faces with four ZnMg8Zn4 cuboctahedra, and faces with twelve MgMg4Zn8 cuboctahedra. There are two shorter (2.97 Å) and two longer (3.04 Å) Mg–Mg bond lengths. There are a spread of Mg–Zn bond distances ranging from 2.88–3.10 Å. In the second Mg site, Mg is bonded to two equivalent Mg and eight Zn atoms to form distorted MgMg2Zn8 cuboctahedra that share corners with four equivalent ZnMg6Zn6 cuboctahedra, corners with twelve MgMg2Zn8 cuboctahedra, edges with nine MgMg4Zn8 cuboctahedra, faces with eight MgMg4Zn8 cuboctahedra, and faces with ten ZnMg8Zn4 cuboctahedra. Both Mg–Mg bond lengths are 3.06 Å. There are a spread of Mg–Zn bond distances ranging from 2.81–2.95 Å. In the third Mg site, Mg is bonded to six Mg and six Zn atoms to form distorted MgMg6Zn6 cuboctahedra that share corners with fourteen MgMg2Zn8 cuboctahedra, an edgeedge with one MgMg2Zn8 cuboctahedra, edges with twelve ZnMg8Zn4 cuboctahedra, faces with six ZnMg8Zn4 cuboctahedra, and faces with twelve MgMg4Zn8 cuboctahedra. Both Mg–Mg bond lengths are 3.04 Å. All Mg–Zn bond lengths are 2.95 Å. There are three inequivalent Zn sites. In the first Zn site, Zn is bonded to eight Mg and four Zn atoms to form distorted ZnMg8Zn4 cuboctahedra that share corners with six equivalent MgMg4Zn8 cuboctahedra, corners with twelve ZnMg8Zn4 cuboctahedra, edges with three equivalent ZnMg6Zn6 cuboctahedra, edges with seven MgMg4Zn8 cuboctahedra, faces with six ZnMg8Zn4 cuboctahedra, and faces with twelve MgMg4Zn8 cuboctahedra. There are two shorter (2.85 Å) and two longer (3.04 Å) Zn–Zn bond lengths. In the second Zn site, Zn is bonded to six Mg and six Zn atoms to form distorted ZnMg6Zn6 cuboctahedra that share corners with ten MgMg4Zn8 cuboctahedra, corners with twelve ZnMg8Zn4 cuboctahedra, edges with three equivalent ZnMg8Zn4 cuboctahedra, edges with eleven MgMg4Zn8 cuboctahedra, faces with six ZnMg8Zn4 cuboctahedra, and faces with eight MgMg4Zn8 cuboctahedra. There are two shorter (2.92 Å) and two longer (3.04 Å) Zn–Zn bond lengths. In the third Zn site, Zn is bonded in a 12-coordinate geometry to eight Mg and two equivalent Zn atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MgZn by Materials Project

MgZn crystallizes in the orthorhombic Amm2 space group. The structure is three-dimensional. there are three inequivalent Mg sites. In the first Mg site, Mg is bonded to eight Mg and four Zn atoms to form MgMg8Zn4 cuboctahedra that share corners with six equivalent MgMg8Zn4 cuboctahedra, corners with twelve ZnMg6Zn6 cuboctahedra, edges with six ZnMg6Zn6 cuboctahedra, faces with four equivalent MgMg8Zn4 cuboctahedra, and faces with four ZnMg6Zn6 cuboctahedra. There are a spread of Mg–Mg bond distances ranging from 3.01–3.05 Å. All Mg–Zn bond lengths are 3.04 Å. In the second Mg site, Mg is bonded in a 12-coordinate geometry to two equivalent Mg and six Zn atoms. There are two shorter (2.81 Å) and four longer (2.94 Å) Mg–Zn bond lengths. In the third Mg site, Mg is bonded in a 12-coordinate geometry to four equivalent Mg and four Zn atoms. There are two shorter (2.83 Å) and two longer (2.88 Å) Mg–Zn bond lengths. There are three inequivalent Zn sites. In the first Zn site, Zn is bonded to six Mg and six Zn atoms to form distorted ZnMg6Zn6 cuboctahedra that share corners with six equivalent MgMg8Zn4 cuboctahedra, corners with twelve ZnMg6Zn6 cuboctahedra, edges with three equivalent MgMg8Zn4 cuboctahedra, edges with three equivalent ZnMg4Zn8 cuboctahedra, faces with two equivalent MgMg8Zn4 cuboctahedra, and faces with six ZnMg6Zn6 cuboctahedra. There are a spread of Zn–Zn bond distances ranging from 2.81–3.05 Å. In the second Zn site, Zn is bonded to four Mg and eight Zn atoms to form distorted ZnMg4Zn8 cuboctahedra that share corners with six equivalent MgMg8Zn4 cuboctahedra, corners with twelve ZnMg6Zn6 cuboctahedra, edges with three equivalent MgMg8Zn4 cuboctahedra, edges with three equivalent ZnMg6Zn6 cuboctahedra, faces with two equivalent MgMg8Zn4 cuboctahedra, and faces with six ZnMg6Zn6 cuboctahedra. There are four shorter (2.94 Å) and two longer (3.05 Å) Zn–Zn bond lengths. In the third Zn site, Zn is bonded in a 12-coordinate geometry to four Mg and six Zn atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Integrated three-dimensional characterization of reactive phase formation and coarsening during isothermal annealing of metastable Zn–3Mg–4Al eutectic

Microstructural instabilities associated with a metastable lamellar eutectic when exposed to an elevated temperature were analyzed in a Zn-3Mg-4Al alloy as a model system. X-ray diffraction and scanning electron microscopy showed that annealing at a temperature 43 K below the equilibrium eutectic temperature converted the metastable ternary MgZn 2 /η-Zn/β-ZnAl eutectic to a stable mixture of Mg 2 Zn 11 /η-Zn/α-Al. 3D EBSD suggested that supersaturation of η-Zn with Mg and Al eased difficulties in nucleation of Mg 2 Zn 11 and α-Al at the MgZn 2 /η-Zn phase interfaces. Quasi-in-situ X-ray nanotomography revealed that a reactive diffusion process prevailed in an early stage of annealing leading to rapid consumption of MgZn 2 for growth of Mg 2 Zn 11 and concomitant thinning and pinch-off of η-Zn lamellae. The reactive diffusion process also brought about significant and quantifiable changes in the topological characteristics of the η-Zn phase at remarkably shorter time scales compared to Rayleigh instability and Ostwald ripening mechanisms. Overall, the present results provide fresh insights on the short-term annealing effects on metastable eutectics, with relevance to structural evolution in additive manufacturing.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Evaluating the bond strength and fracture mechanisms of cold-sprayed zinc coating on AZ91 magnesium substrate via a combined experimental and computational approach

Magnesium (Mg) alloys are ideal candidates for automotive applications due to their high strength to weight ratio, castability, recyclability etc., however, they lack corrosion and oxidation resistance. Solid-state deposition techniques, such as cold spray, have been demonstrated to enhance their corrosion resistance as it relies on the severe plastic deformation of powder particles upon impact with the substrate to form a metallurgical bond with the substrate and within the coating. At cold sprayed interfaces, a heterogeneous microstructure is formed that includes some porosity, oxides and intermetallics which can significantly affect coating performance. Thus, establishing a direct correlation between the interface microstructure and its properties can aid in designing optimal cold spray parameters. In this study, we investigated the microstructure and mechanical properties of a zinc (Zn) coating deposited on a high pressure die cast (HPDC) AZ91 Mg substrate via high resolution scanning transmission electron microscopy, in situ micro-tensile testing, and finite element method (FEM) modeling. Micro-tensile pillars fabricated using the plasma focused ion beam (PFIB) successfully isolates the coating-substrate interface within the gauge length. The average bond strength of Zn-Mg interface was determined to be ∼140 MPa with failure occurring partially at the interface and mostly into the coatings. A detailed microstructural characterization revealed evidence of a strong metallurgical bonding at the Zn-Mg interface and formation of the C14 MgZn 2 laves phase interlayer resulting in a mixed mode of fracture during the micro-tensile experiments. FEM modeling reveals the stress distribution along the interfaces and suggests that a MgZn 2 layer thickness between 200–400 nm is optimum to increase the bond strength and minimize the triaxiality. Such a site-specific interfacial analysis with correlative computational modeling provides crucial insight into the overall performance of cold spray interfaces.

Bond strength↗
DOE OSTI2024

Comparison of Mg-based liquid metal ion sources for scalable focused-ion-implantation doping of GaN

We compare the suitability of various magnesium-based liquid metal alloy ion sources (LMAISs) for scalable focused-ion-beam (FIB) implantation doping of GaN. We consider GaMg, MgSO 4 $\bullet$7H 2 O, MgZn, AlMg, and AuMgSi alloys. Although issues of oxidation (GaMg), decomposition (MgSO 4 $\bullet$7H 2 O), and excessive vapor pressure (MgZn and AlMg) were encountered, the AuMgSi alloy LMAIS operating in a Wien-filtered FIB column emits all Mg isotopes in singly and doubly charged ionization states. We discuss the operating conditions to achieve <20 nm spot size Mg FIB implantation and present Mg depth profile data from time-of-flight secondary ion mass spectrometry. We also provide insight into implantation damage and recovery based on cathodoluminescence spectroscopy before and after rapid thermal processing. Prospects for incorporating the Mg LMAIS into high-power electronic device fabrication are also discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Microstructure evolution, enhanced aging kinetics, and mechanical properties of AA7075 alloy after friction extrusion

In the present study we utilized Friction Extrusion (FE) a solid phase processing technique to produce fully consolidated dense 5 mm rods of AA7075 alloy. The combination of large shear stresses and temperatures at the tool-billet interface during the FE process resulted in the formation of dynamically recrystallized ~2.0 μm equiaxed grains and fine uniformly distributed stable η (MgZn 2 ) precipitates ~25–100 nm in size. Formation of such a microstructure resulted in lower solutionizing temperature and times (flash annealing) as compared to the conventionally extruded counterparts. Here we demonstrate for the first time that the solutionizing times for the T6 heat treatment of AA7075 can be reduced by three times using this FE process. In addition to being an energy efficient process, FE also serves to improve the performance of AA7075 alloys by retaining their strength while enhancing the ductility of the material. The tensile data for samples that were flash annealed and artificially aged after FE processing showed exceptional increase in ultimate tensile strength by over 19% and yield strength by over 59%, compared with an as-FE-processed sample.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Three dimensional cluster analysis for atom probe tomography using Ripley’s K-function and machine learning

The size and structure of spatial molecular and atomic clustering can significantly impact material properties and is therefore important to accurately quantify. Ripley’s K-function (K(r)), a measure of spatial correlation, can be used to perform such quantification when the material system of interest can be represented as a marked point pattern. This work demonstrates how machine learning models based on K (r)-derived metrics can accurately estimate cluster size and intra-cluster density in simulated three dimensional (3D) point patterns containing spherical clusters of varying size; over 90% of model estimates for cluster size and intra-cluster density fall within 11% and 18% error of the true values, respectively. These K (r)-based size and density estimates are then applied to an experimental APT reconstruction to characterize MgZn clusters in a 7000 series aluminum alloy. Here we find that the estimates are more accurate, consistent, and robust to user interaction than estimates from the popular maximum separation algorithm. Using K (r) and machine learning to measure clustering is an accurate and repeatable way to quantify this important material attribute.

36 MATERIALS SCIENCE↗