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TMS-DGM Symposium: A Joint US-European Symposium on Linking Basic Science to Advances in Manufacturing of Lightweight Metals: Session I
Sponsored by: Deutsche Gesellschaft für Materialkunde e.V. (DGM): German Materials Society , TMS Materials Processing and Manufacturing Division, TMS: Shaping and Forming Committee
Program Organizers: William Joost; Norbert Hort, Helmholtz-Zentrum Hereon

Wednesday 8:30 AM
March 17, 2021
Room: RM 26
Location: TMS2021 Virtual

Session Chair: William Joost, Pratt & Whitney

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8:30 AM  
Stacking-fault Mediated Plasticity and Strengthening in Lean, Rare-earth Free Magnesium Alloys: Indranil Basu¹; Jörg Löffler¹; ¹ETH Zurich
    A magnesium alloy with lean additions of Zn (1wt.%) and Ca (0.3wt.%), ZX10, and pure Mg were subjected to orientation-dependent micropillar indentation tests at room-temperature. Two different orientations of single-crystalline micropillars were fabricated to activate c-axis extension and c-axis compression. For both loading conditions, ZX10 reveals a strengthening increment by a factor of 2 to 2.5 compared to pure Mg, plus simultaneous plasticity enhancement. Under c-axis extension, correlative transmission EBSD and TEM reveals that deformation in ZX10 proceeds via twinning plus activation of homogeneous basal and non-basal slip at higher strains, whereas pure Mg reveals deformation through tension twinning and basal slip. In c-axis compression, ZX10 shows dual activation of basal <a> and pyramidal <c+a> dislocations, while pure Mg deforms by basal dislocation-mediated massive sliding. We illustrate how minute additions of Zn and Ca solutes modify intrinsic stacking-fault energies and thus are able to generate significant strength and ductility enhancement.

8:50 AM  
High-throughput Evaluation of Hardening Potency and Solubility of Eight Alloying Elements in Magnesium: Chuangye Wang¹; Wei Zhong¹; Ji-Cheng Zhao¹; ¹University Of Maryland
    Liquid-solid diffusion couples (LSDCs) were able to generate the complete single-phase hcp solid solution compositions up to the solubility limit. Nanoindentation scans across the composition gradient in LSDCs allowed effective evaluation of composition-dependent hardness of eight alloying elements (Al, Ca, Ce, Gd, Li, Sn, Y, Zn) in the hcp Mg phase. The solute hardening coefficients were evaluated from the measured composition-hardness data and correlated with various properties such as atomic radius of the solutes. The hardening coefficients which are an indicator of the potency of solid-solution strengthening were found to be best correlated with the computed strengthening rates of the solutes. The composition profiles obtained from the LSDCs also allowed reliable evaluation of the solubility limits of these elements in the hcp Mg phase at various temperatures to provide valuable data for phase diagram and thermodynamic assessments. The solubility data are the first measurements for some of these elements.

9:10 AM  
High-throughput Experimental Techniques to Measure the CRSS for Slip and Twinning in Mg and Mg Alloys: Jingya Wang¹; Reza Alizadeh²; Javier Llorca³; ¹Shanghai Jiao Tong University and IMDEA Materials Institute; ²Sharif University of Technology and IMDEA Materials Institute; ³IMDEA Materials Institute & Technical University of Madrid
    Alloying Mg with different elements improves the strength and modify the plastic anisotropy. However, the accurate determination of the effect of solute atoms and precipitates on the CRSS of each slip is very expensive because it requires the manufacturing of single crystals with different composition and orientations. This problem may be overcome by the combination of micropillar compression tests and high-throughput processing techniques based on the diffusion couples. This methodology requires a detailed analysis of the effect of micropillar dimensions on the flow strength and can be easily extended to high temperatures. Using this methodology, the effect of Al and Zn in solid solution on the CRSS for basal and pyramidal slip and twinning as well as of MgZn2 precipitates on basal and pyramidal slip was determined. The results were compared with predictions from atomistic and/or continuum models and showed the effect of alloying on the strength and plastic anisotropy.

9:30 AM  
Study of the Solidification Pathways of Hypo/hyper-eutectic Al-Ce over a Wide Range of Thermal Histories: Akankshya Sahoo¹; Abdoul Aziz Bogno¹; Hani Henein¹; ¹University of Alberta
    High temperature (>300°C) applications of precipitation-strengthened Al-alloy are limited by coarsening or dissolution of the strengthening precipitates. Unlike the conventional Al-alloys, the strengthening Al11Ce3 intermetallic in Al-Ce is very stable at high temperatures, making the alloy microstructurally and mechanically stable. In addition, the precipitation of Al11Ce3 does not require post-processing heat treatment, making the alloy economically attractive. Tailoring Al-Ce alloys for specific applications requires the knowledge of their microstructure formation over a wide range of thermal histories. This work reports on the solidification-developed microstructures, over a wide range of cooling rates (0.1-10^4K/s), of hypo/hyper-eutectic binary Al-Ce and Al-Ce-X multicomponent alloys generated by DSC and Impulse Atomization. Qualitative and quantitative microstructural characterization were conducted using XRD, OM, SEM, EPMA to determine the influence of cooling rate and Ce concentration. The solidification pathways and resulting microstructures were subsequently determined and a critical relationship between processing/microstructure/properties of Al-Ce alloys was developed.

9:50 AM  
Solute-vacancy Clustering in Aluminum: Dongwon Shin¹; Jian Peng¹; Sumit Bahl¹; Amit Shyam¹; James Haynes¹; ¹Oak Ridge National Laboratory
    We present a first-principles database of solute-vacancy, homoatomic, heteroatomic solute-solute, and solute-solute-vacancy binding energies of relevant alloying elements in aluminum. We particularly focus on the systems with major alloying elements in aluminum, i.e., Cu, Mg, and Si. The computed binding energies of solute-vacancy, solute-solute pairs, and solute-solute-vacancy triplets agree with available experiments and theoretical results in literature. We consider physical factors such as solute size and formation energies of intermetallic compounds to correlate with binding energies. Systematic studies of the homoatomic and heteroatomic solute-solute-vacancy complexes reveal the overarching effect of the vacancy in stabilizing solute-solute pairs. The binding energy database presented here elucidates the interaction between solute cluster and vacancy in aluminum, and it is expected to provide insight into the design of advanced Al alloys. The research was sponsored by the LDRD Program of Oak Ridge National Laboratory and the Department of Energy, Vehicle Technologies Office, Propulsion Materials Program.

10:10 AM  
Fracture Mechanisms under Monotonic Tensile, Fatigue, and Creep Deformation of Cast Al-Cu-Mn-Zr Alloys: Impact of Brittle Intermetallic Grain Boundary Particles: Sumit Bahl¹; Xiaohua Hu¹; Jiahao Cheng¹; Eric Hoar²; Kevin Sisco³; Richard Michi¹; J. Allen Haynes¹; Amit Shyam¹; ¹Oak Ridge National Laboratory; ²Georgia Institute of Technology; ³University of Tennessee-Knoxville
    Cast aluminum alloy microstructures often contain brittle intermetallic phases that can impact the alloy’s fracture behavior. Here, we describe a set of higher temperature cast Al-Cu-Mn-Zr (ACMZ) alloys containing 6 – 9 wt.% Cu, designed to have controlled fraction of brittle intermetallic grain boundary θ (Al₂Cu) particles in the microstructure. The designed set of alloys allows for a systematic investigation into the impact of brittle θ particles on fracture behavior of ACMZ alloys under various deformation modes including monotonic tensile, low cycle fatigue, and creep. These deformation modes are relevant for higher temperature Al alloys, specifically used in automotive engine applications. Microstructural characterization and finite element simulations are used to explain the contrasting effects of θ particles noted on fracture mechanisms as a function of deformation mode with potential implications on alloy design and development.

10:30 AM  
Al-Fe-Si Phase Stabilization Using Experimentally Validated Computational Thermodynamics: Sujeily Soto-Medina¹; Biswas Rijal¹; Lilong Zhu²; Richard Hennig¹; Michele Manuel¹; ¹University of Florida; ²Yantai University
    The Al-Fe-Si alloy system provides an opportunity for the development of low-cost, lightweight, high-temperature alloys. Specifically, the τ₁₁-Al₄Fe_1.7Si ternary intermetallic phase is a high temperature lightweight phase with the potential to demonstrate both high-strength and good corrosion resistance. However, this phase exhibits a small compositional range of stability. The present study discusses a design approach integrating computational and experimental work to increase the stability range of τ₁₁-Al₄Fe_1.7Si phase with additions of Mn. Density Functional Theory calculations were performed to predict the favorable Mn composition and site occupancies in τ₁₁. The calculations guided the diffusion couple and equilibrated alloy experiments. The diffusion couple experiments measured the phase boundary of the τ₁₁ with addition of Mn. The results demonstrate that the stability range of the τ₁₁ phase can be increased by an alloy design approach that identifies a pathway for energetic and entropic stabilization.

10:50 AM  
Spatial Correlations between Strengthening Particles in Multi-phase Hardenable Aluminum Alloys: Viktor Wessely¹; Robin Schäubin¹; Stephan Gerstl¹; Stefan Pogatscher²; Peter Uggowitzer¹; Jörg Löffler¹; ¹Laboratory of Metal Physics and Technology; ²Montanuniversitaet Leoben,
    We focus on a new generation of hardenable aluminum alloys based on the formation of coherent Al₃X L1₂-structured dispersoids. Suitable alloying elements are, amongst others, Zr and Hf, which are known to strengthen the material while providing exceptional high-temperature stability due to their low diffusivity. Thermodynamic and kinetic modeling is deployed to design alloys and their heat treatments, with subsequent mechanical and microstructural characterization. The dispersoids form as an ordered phase coherent with the fcc matrix. Studying their evolution in Al–Mg–Zn alloys with <1 wt.% Hf and Zr, we find that the Al₃X dispersoids have a significant impact on the alloys’ hardening characteristics. Detailed insights into the microstructure obtained by a multi-scale microstructural analysis based on high-end transmission electron microscopy (TEM) and atom-probe tomography (APT) reveal that the key to a successful alloy design lies in controlling the spatial correlation between the dispersoids and precipitate phase.

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