Magnesium Technology: On-Demand Oral Presentations
Sponsored by: TMS Light Metals Division, TMS: Magnesium Committee
Program Organizers: Petra Maier, University of Applied Sciences Stralsund; Steven Barela, Terves, Inc; Victoria Miller, University of Florida; Neale Neelameggham, IND LLC
Monday 8:00 AM
March 14, 2022
Room: Light Metals
Location: On-Demand Room
The Comparability of In Vitro and In Vivo Experiments for Degradable Mg-implants: Regine Willumeit Romer1; Stefan Bruns1; Heike Helmholz1; Norbert Hort1; Diana Krueger1; Yu Sun1; Bjoern Wiese1; Berit Zeller-Plumhoff1; 1Helmholtz-Zentrum Hereon
Mg implants pose a great potential for clinical applications. Thousands of patients are already successfully treated with Mg implants, and more products get approval. Despite the fact that it works we know that we have not yet reached full understanding of all processes which occur during the degradation of the material and tissue regeneration. We might perhaps never come to a complete description of the physical, chemical and biological processes during healing. And perhaps it is not necessary to fully unravel all details of the reactions and interactions. We already can conclude that in vitro experiments can predict many observations found in vivo with a sufficient precision. This presentation will give an overview of what we know for in vitro, in vivo degradation as well as in vivo imaging (synchrotron radiation tomography), and histology, their limitations and how to overcome them.
Multi-functional Ceramic Coatings for Corrosion Protection of Magnesium Alloys: Beatriz Mingo1; Yue Guo1; Safiya Al Abri1; Allan Matthews1; Aleksey Yerokhin1; 1The University of Manchester
The increasing demand for magnesium-based materials for transportation has led to the development of surface treatments to enhance their performance. Active coatings stand out due to their ability to provide on-demand functionalities such as corrosion inhibition or self-healing. The current outlook on smart protection methods is dominated by organic-based materials, which present poor mechanical and thermal resistance that limits their applicability.This work pursues a new approach to achieve the active functionalisation of ceramic- coatings, which inherently present excellent physical and chemical stability at high temperatures and exceptional performance in aggressive environments. The multi-functionalisation relies on the combined response of the ceramic matrix that provides long-term wear protection, with the incorporation of encapsulated inhibitors into nanocontainers that offer corrosion protection on demand. The inhibitors are released into the media when detecting pH changes arisen from electrochemical activity and will act locally at the anodic and cathodic sites inhibiting corrosion propagation.
Development of Flame-retardant Wrought Magnesium Alloys and Application of the Alloys to High-speed Railway Body: Yasumasa Chino1; Kazunori Shimizu2; Futoshi Kido3; Takeshi Ishikawa4; Makoto Taguchi5; Hisashi Mori1; Takao Horiya6; 1National Institute of Advanced Industrial Science and Technology; 2Sankyo Tateyama, Inc.; 3Fuji Light Metal Co., Ltd.; 4Japan Transport Engineering Company; 5Kawasaki Heavy Industries, Ltd.; 6Innovative Structural Materials Association
Application of “flame retardant magnesium (Mg) alloy”, which is defined as Mg-Al alloy with 0.5-2.0mass%Ca, is an effective way to improve flame retardance. In Japan, the national project of “Innovative Structural Materials R&D” has been launched since 2013FY. In the project, flame-retardant Mg wrought alloys for their allocation to high-speed railway bodies have been conducted. In the first half of the project, wrought Mg-Al-Ca alloys corresponding to A6005C (Al-Mg-Si) and A7204 (Al-Zn-Mg) alloys have been developed, where AX41 (Mg-4%Al-1%Ca (mass%)) alloy with superior extrudability corresponding to A6005C alloy, AX92 (Mg-9%Al-2%Ca) and AX81 (Mg-8%Al-1%Ca) alloys with good balance in mechanical properties corresponding to A7204 alloy, have been developed. After the development of the new alloys, as a next step, a prototype, which imitates railway vehicle body with 1/1 scale cross-section, has been produced with the purpose of verifying their assembling ability, forming ability, joining ability, cutting ability, surface treatment ability.
On the Mechanical Behaviors of Extruded AZ61A Magnesium Alloy Tube under Cyclic Torsion: Xiaodan Zhang1; Qin Yu2; Huamiao Wang1; 1Shanghai Jiao Tong University; 2Lawrence Berkeley National Laboratory
Load bearing structural components of magnesium alloys are sometimes subjected to cyclic shear. Therefore, understanding the mechanical behavior of magnesium alloys under cyclic shear is essential for the design, fabrication, and service of the end products. In this work, the cyclic torsion tests of extruded AZ61A Mg alloy tube are conducted. In parallel, the elastic viscoplastic self-consistent model with the twinning and detwinning scheme, in conjunction with a torsion specific finite element approach, is employed to model the cyclic torsion. The results reveal that the deformation mechanisms alter significantly with varying the different loading, leading to variances in Swift effect, the twin volume fraction and relative activities of deformation mechanisms.
Towards Improving Cold Formability of Concentrated Mg-Al-Zn-Ca Alloy Sheet: Mingzhe Bian1; Xinsheng Huang1; Yasumasa Chino1; 1National Institute of Advanced Industrial Science and Technology
Concentrated Mg-Al-Ca(-Zn) sheet alloys have numerous advantages such as excellent flame retardancy, good corrosion resistance, high strength, and more importantly low material cost. However, poor formability at room temperature (RT) has been the main bottleneck for their wider applications. In this talk, we will demonstrate that the high temperature final rolling could be one of the strategies to improve the RT stretch formability of concentrated Mg-Al-Zn-Ca alloys. A Mg-6Al-1Zn-1Ca alloy sheet subjected to 510 °C final rolling shows an index Erichsen value of 7.9 mm, which is significantly higher than that of the same sheet subjected to 450 °C final rolling (4.1 mm). More excitingly, 510 °C final rolled Mg-6Al-1Zn-2Ca alloy sheet exhibits a large I.E. value of 8.0 mm which has never been achieved in 2 wt% Ca-containing Mg alloys.
A Method for Crystal Plasticity Model Parameter Calibration Based on Bayesian Optimization: Xiaochuan Sun1; Huamiao Wang1; 1Shanghai Jiao Tong University
Crystallographic plasticity model is an efficient method to bridge the mechanical characteristics of a material at the crystallographic scale to the macroscopic mechanical responses. However, the relatively large number of model parameters makes the calibration cumbersome, especially in systems with hexagonal close packed (HCP) structures like magnesium alloys. This work presents a Bayesian Optimization-based approach and applied it to the calibration of the viscoplastic self-consistent polycrystal plasticity model with twinning and de-twinning scheme (VPSC-TDT) to describe the mechanical behavior of the rare-earth magnesium alloy ZEK100. The result shows that Bayesian Optimization can perform well in such a physical principle-based black-box optimization problem. Combined with a practical tactic, the total trial number can be reduced to around 100, efficiently reducing the time cost. The obtained optimized set of parameters can successfully reproduce the loading path-dependent mechanical behavior of the Mg alloy ZEK100.
The Role of Ordered Phases in Enhanced Ductility of RE Based Mg Alloys: Henry Ovri1; Erica Lilleodden1; 1Helmholtz Zentrum Hereon
Various experimental and modelling efforts confirm that low concentrations of rare earth (RE) solutes in Mg enhances the room temperature ductility and weakens the deleterious basal texture that occurs during sheet forming of classical wrought Mg alloys. However, the mechanistic origin(s) of the improved ductility and texture weakening are still been debated. In order to gain insights into the underlying governing mechanisms, we carried out in-depth characterization of the dislocation strengthening behavior in single crystals of pure Mg and a Mg–4.69 wt% Gd alloy oriented for basal and pyramidal slip. We postulate that the remarkable differences in dislocation slip activity observed between these two systems, along with significant decreases in non-basal/basal CRSS slip ratios, strongly suggest that the improved formability of the RE-based Mg alloys is a consequence of ordered domains and precipitates that lie mainly on the basal planes of the alloy.
Investigation on the Effect of Si Addition in Controlling the Microstructure of Mg-4wt%Al-4wt%RE Alloy: Vigneshwar Hari1; Dongdong Qu1; Trevor Abbott2; Kazuhiro Nogita1; 1The University of Queensland; 2RMIT University
The structural light metal AE44 with the composition Mg-4Al-4RE (RE: rare earth) has a high specific creep resistance which makes it a promising alloy applied in industry. In this work, the RE element is tried as pure La, pure Ce and a mixture of La and Ce of different ratios. The effect of trace Si addition into the AE44 alloy system is studied via investigating the variation of the cast ingot microstructure. It is found that 0.1% Si managed to modify La contained intermetallic in the Mg-4Al-4La system. The solidification mechanism of the Si modified AE44 alloy is discussed based on the calculated thermodynamic assisted by ThermoCalc.
Microstructure and Texture Analysis of Dissimilar Friction Stir Welded AZ31 Mg and Al 6061 Joint: Nikhil Gotawala1; Amber Shrivastava1; 1Indian Institute of Technology Bombay
The objective of this work is to analyze the microstructure and texture upon friction stir welding of AZ31 Mg and Al 6061 alloys. Various light-weighting applications prompt for welding of Mg alloys with another material. Friction stir welding has shown potential to join dissimilar materials, with limited formation of undesirable intermetallics. The joint performance is affected by the texture and microstructure, which evolve during the process owing to higher temperature plastic deformation. The friction stir welding of AZ31 Mg and Al 6061 is performed at 100 mm/min feed rate and 500 rpm tool rotation speed with 2° tilt angle. In the stir region, both materials have undergone grain refinement. However, the stir region itself is asymmetrical with respect to the tool centreline and higher grain refinement is observed on the AZ31 Mg side. Further, basal texture and shear texture are noticed on the AZ31 Mg and Al 6061 sides, respectively.
Influence of Third Alloying Element on Dislocation Slip and Twinning Activities in Mg-Nd Based Alloys: Xun Zeng1; Dietmar Letzig2; Karl Kainer3; Dikai Guan1; Sangbong Yi2; 1The University of Sheffield; 2Institute of Material and Process Design, Helmholtz – Zentrum Hereon; 3Light Elements Engineering, Foundry and Automation, Wrocław University of Science and Technology
The influence of Zn or Al addition as third alloying element on the deformation mechanisms of Mg-Nd based alloys was investigated by quasi in-situ tension. Distinct mechanical behaviors were observed between Mg - 1.0 Zn - 1.7 Nd (ZN12, in wt.%) and Mg – 1.0 Al – 1.7 Nd (AN12) alloys. The ZN12 alloy showed lower yield strength and higher fracture strain compared to the AN12. A considerable number of slip traces, corresponding to basal and non-basal dislocations, were formed at the early deformation stage of the ZN12 sample. On the contrary, only a few grains in the AN12 sample showed obvious slip traces. Half of the twins were formed after yielding in the ZN12 sample, while the majority of the twins were formed at higher strain in AN12. Twin growth was more obvious in the AN12 sample due to insufficient active deformation modes than in the ZN12 sample.
Accelerated Micromechanical Response Prediction Using a Deep Network-based Surrogate Model: Wei Dai1; Huamiao Wang1; 1Shanghai Jiao Tong University
Deep network-based material models provide advantageous computational efficiency over classical crystal plasticity simulations. In this work, a deep network-based surrogate model, more specifically, a Gated Recurrent Unit (GRU) model, is proposed to address the microstructure-sensitive and history dependent response. Visco-plastic self-consistent model incorporating the twinning and detwinning (VPSC-TDT) scheme is used for training the GRU to capture the mechanical response of ZEK100 magnesium alloy sheet. Considering disorder of high-dimensional texture data, a similar PointNet is developed to automatically learn low-dimension representation of microstructure. Subsequently, GRU is used to learn the plasticity-constitutive relations such that it can predict the stress histories of various microstructures and loading paths. This work demonstrates that deep network-based models trained by micromechanical simulations capture material behavior and its relation to microstructural mechanisms in a physically sound way. Compared to crystal plasticity models, the proposed model not only significantly accelerates the simulations, but also sustains a comparable accuracy.
Effect of Microstructural Refinement and Na Addition on Hydrogenation Kinetics of Cast Mg-Al-La Alloy during the First Hydrogen Absorption Process: Manjin Kim1; Stuart McDonald1; Yahia Ali1; Trevor Abbott2; Kazuhiro Nogita1; 1The University of Queensland; 2Magontec Ltd.
Long activation cycles, slow sorption kinetics, and high desorption temperature have been obstacles that hinder commercialisation of Mg-based alloys for hydrogen storage systems. Previously, it has been demonstrated that fine eutectic microstructure and trace Na additions to binary Mg-based alloys such as Mg-Ni and Mg-La improve hydrogen absorption kinetics during the first absorption cycle. However, no study about the effect of eutectic microstructure and Na additions on hydrogen absorption kinetics of ternary Mg-based alloys has been reported. In this work, we have extended this technique to an Mg-Al-La ternary alloy. The result shows that Na addition causes coarser eutectic structure in the alloy however improves hydrogen absorption kinetics. The mechanisms of absorption kinetics improvement via Na addition are discussed in terms of microstructure change and chemical effect of Na during hydrogen absorption process.
Effective Dispersion of Stable Quasicrystals in ZW82 and ZA63 Alloys for Strengthening: Karel Tesar1; Hidetoshi Somekawa2; Alok Singh2; 1Czech Technical University in Prague; 2National Institute for Materials Science
Magnesium alloys reinforced with quasicrystalline icosahedral (i-) phase have been reported to show very high strength combined with good ductility due to very fine grain size and moderate texture on extrusion. Here we show that on processing by extrusion in two steps, ZW82 (Mg-3Zn-0.5Y in at%) and ZA63 (Mg-2.3Zn-2.8Al in at%) alloys show a uniform distribution of i-phase particles, resulting in homogeneous microstructure such as uniform grain size. Phase (particle) distribution, grain structure, microtexture and related parameters were determined. Mechanical behavior was evaluated by tensile and compression tests. Finer particle distribution resulted from breakage and refinement of the existing particles, resulting in full recrystallization reported in ZW82 for the first time. Consequently, a tension-compression yield symmetry was achieved even with a relatively large grain size of about 5 micron. Precipitation of stable i-phase was discovered in ZW82 alloy. I-phase precipitates exerted a strong pinning effect on grain boundaries.
Characterizing Precipitate Composition and Grain Boundary Segregation Behavior in Mg-alloys: Qianying Shi1; John Allison1; 1University of Michigan
The fine precipitates and grain boundary segregation are critical microstructural features at the nano-scale level in Mg alloys. These features influence the properties of Mg-alloys via precipitation strengthening and grain boundary strengthening and can also influence texture, recrystallization and deformation behavior. In this study, Mg-alloys containing different alloying elements, specifically, Nd, Y, Ca and Zn have been investigated to understand the elemental distribution behavior in precipitates and grain boundaries. Qualitative and quantitative characterization of the elemental segregation was conducted via a series of advanced material characterization techniques, including FIB lift-out, HRSTEM, HAADF, fast STEM-EDS and 3D-APT reconstruction. Our initial results indicate that non-rare earth element Ca segregates into nano-precipitates along with rare earth elements Nd and Y, which is believed to contribute the precipitation strengthening. Meantime, the grain boundary segregation of Y, Zn and Ca is observed, which accounts for the texture modification and the formability improvement of Mg-alloys.
In-situ Analysis on Formation and Development of LPSO-like Nanostructures in Dilute MgYZn and MgGdZn Alloys: Hiroshi Okuda1; Michiaki Yamasaki2; Yoshihito Kawamura2; 1Kyoto University; 2Kumamoto University
Controlling formation of partial structures of long-period stacking ordered structure in dilute MgYZn alloys has been expected to be a prospective approach to strengthen Mg based materials without increasing specific weight. To understand the formation kinetics, however, in-situ approach is important, since phase transformation process in dilute MgYZn alloy is expected to be thermal history dependent, and many intermediate structures may appear. We performed in-situ small- and wide angle scattering measurements to examine nanostructural evolution during heat treatments. Mg100-x-yYxZny and Mg100-x-yGdxZny alloys have been heat up to annealing temperatures in-situ. Two well-defined clustering region was found for both alloys: clusters formed at lower temperatures once disappears before stable L12 clusters are formed at higher temperatures. Clusters at lower temperatures were reported to be less effective for strengthening.
Exploring the Microstructure-property Relationship of Mg-Al-Mn Alloys Enhanced via Friction Stir Processing: David Garcia1; Hrishikesh Das1; Xiaolong Ma1; Timothy Roosendaal1; Vineet Joshi1; Darrell Herling1; Mageshwari Komarasamy1; Glenn Grant1; 1Pacific Northwest National Laboratory
Friction Stir Processing (FSP) is a solid-state thermomechanical processing technique that enables local grain refinement, densification, and homogenization of microstructure in metallic components. Here, FSP is applied to thin sheets of high-pressure die cast AM60 to address the porosity and heterogeneities inherent to the casting process. In this work, microstructure characterization is correlated to improvements in the static mechanical properties of the Mg alloys at various FSP processing conditions. Furthermore, the dominant deformation mechanisms for the as-cast material and the FSP material are investigated. Finally, the fatigue life improvement is correlated to microstructure modifications that lead to distinct behavior in crack initiation and crack propagation for the as-cast and FSP material.
Improving the Corrosion Behavior and Mechanical Properties of Biodegradable Mg-Zn-Zr Alloys through ECAP for Usage in Biomedical Applications: Waleed El-Garaihy Nasr1; Abdulrahman Alateyah1; Majed Alawad2; Talal Aljohani3; 1Qassim University; 2King Abdulaziz City for Science and Technology ; 3King Abdulaziz City for Science and Technology
ZK30 Magnesium alloy shows a great potential for usage in biomedical implants; however, the only setback to the alloys’ usage is their corrosion properties. For that end, extruded ZK30 billets were processed through ECAP for up to 4-passes of route Bc. FE analysis was used to study the deformation behavior of the ZK30 billets during processing. The alloy’s microstructural evolution was monitored through electron backscatter diffraction (EBSD). The corrosion behavior of the ZK30 alloy was studied before and after ECAP processing. Vicker’s microhardness distribution along the longitudinal and transverse sections were evaluated and correlated to the EBSD findings. FE simulation displayed fairly homogenous distribution of the plastic strain along both the longitudinal and transverse sections after processing through 4-Bc. Furthermore, ECAP processing via 4-Bc resulted in a significant decrease of 92.7% and 94% in the average grain size and corrosion rate, respectively compared to the as-annealed condition. On the other hand, Vicker’s microhardness finding revealed a fairly homogenous distribution along both the longitudinal and transverse sections recording a significant increase of 96% compared to the AA counterpart after 4-Bc passes. Accordingly, the corrosion and hardness findings conclude that ECAPed ZK30 alloys are a viable option, endorsing further research into the alloys, for usage in biodegradable implants, and they show great potential for usage in industry.
Development of Magnesium-lithium Based Alloys for Space Applications: The Relationship between Precipitation Hardening and Damping Capacity: Florian Schott1; David McKeown1; Li Jin2; Mert Celikin1; 1University College Dublin; 2Shanghai Jiao Tong University
For developing lighter miniaturised satellite frame structures (CubeSat), which will allow additional payload as well as more design freedom, Magnesium-Lithium (Mg-Li) based alloys were investigated to potentially replace commonly used aluminium (Al) alloys. The effect of age-hardening treatment in comparison to Al-based alloys on damping performance were analysed using Dynamic Mechanical Analysis (DMA). Dynamic cantilever bending was performed for measuring viscoelastic properties and particularly the loss factor at varying temperatures under solution-treated, age-hardened and over-aged conditions. Moreover, thermally induced precipitates were characterized using Transmission Electron Microscopy (TEM) upon age-hardening treatment conducted at 150˚C and 200˚C. A direct link between the second phase formation and viscoelastic properties of the alloys was determined.
Assessment of Extruded Magnesium Tubing for Absorbable Stent Production: Adam Griebel1; Gregory Hayes2; Robert Werkhoven2; Roman Menze3; Jeremy Schaffer1; 1Fort Wayne Metals; 2Complex Materials; 3MeKo Laser Material Processing
Stents are tubular medical devices used to provide internal support to lumens throughout the cardiovascular, respiratory, gastrointestinal, and urinary systems. Stents composed of absorbable metals like magnesium can provide temporary structural support and then be absorbed into the body, allowing the vessel to return to a natural state. Manufacturing of high-quality magnesium alloy stents is non-trivial, and care must be taken through the entire process from ingot melting to laser cutting. The aim of this study was to demonstrate a viable manufacturing path for such stents. Specifically, bars of two alloys (ZX10 and LZ21) were produced by Fort Wayne Metals, extruded into fine-grained tubing through a unique extrusion process at Complex Materials, and laser machined and electropolished at MeKo. The microstructural and mechanical behavior of the resultant stents was assessed and compared to a reference WE43 material. Future work will include coating application and degradation assessments.
High Performance Mg-4Al-4RE (RE = Cerium and Lanthanum) Die-casting Alloy: Hua Qian Ang1; Suming Zhu1; Trevor Abbott2; Mark Easton1; 1RMIT University; 2Magontec Limited
This paper presents an overview of the recent development of die-cast Mg-4Al-4RE (AE44, where RE is a mixture of Cerium and Lanthanum) to highlight some of its characteristics which differ from other magnesium alloys. Die-cast AE44 exhibits a distinct hardening response upon ageing (T5) due to precipitation of nanoscale Al-Mn particles. The T5 ageing leads to a significant improvement in strength without reducing the ductility in AE44. Hence, T5-aged AE44 has a better strength-ductility combination than other magnesium die-casting alloys. AE44 also exhibits high strain-rate sensitivity, which manifests as an increase in work hardening with increasing strain rate. The amount of anelasticity in AE44 is also quantified and some significant anelasticity is observed at low stress-strain levels. A higher offset strain method is proposed to improve the accuracy of yield strength measurement for die-cast magnesium alloys. It is shown that the properties of AE44 exceed many aluminium casting alloys.
Unraveling Mg <c+a> Slip Using Neural Network Potentials: Christopher Barrett1; Mashroor Nitol1; Doyl Dickel1; 1Mississippi State University
Magnesium (Mg) activates <c+a> dislocation slip on the second order pyramidal slip plane. Historically, under c-axis compression there has been a discrepancy in the preferred pyramidal slip plane as measured by experiments versus atomistic simulations. Here we compare atomistic simulation results using several interatomic potentials including a novel artificial neural network (RANN) potential with the aim of determining whether this discrepancy arises from interatomic potential inaccuracies. The new potential shows better agreement with density functional theory and experimental calculations than previous interatomic potentials for Mg. The new results are confirmed by another independent neural network potential. We demonstrate that the basal dissociated <c+a> core is glissile at low stress, completely contrary to previously thought, and that constant stress molecular dynamics demonstrate clear preference for the 2nd order pyramidal system over the 1st order system.
Cancelled
The Effect of Scandium on the Electronic and Transport Properties of MgO: Amall Ramanathan1; 1The University of Jordan
The electronic and transport properties of Mg1-xScxO (x=0, 0.25, 0.5 and 1) alloys are investigated using the first principles total energy pseudopotential method under the density functional theory (DFT). Since Mg and Sc atoms have comparable sizes, the substitution of Sc for Mg in the conventional unit cell of the rock salt structure of MgO is viable.The relaxed structures of the alloys are used to elucidate the electronic and transport properties using the semi-classical Boltzmann transport theory.
Quantifying the Influence of Coarse Intermetallic Particles on Twin Transmission: Benjamin Anthony1; Victoria Miller1; 1University of Florida
Understanding and controlling deformation twinning behavior is of critical interest to magnesium alloys and other HCP metals as this mechanism can help accommodate strain; however, this mechanism also provides a preferential crack pathway along the twin boundary. This is particularly the case during instances of twin transmission, where a twin impinging on a grain boundary nucleates an adjacent twin in the neighboring grain due to intense local stresses. Many commercial Mg alloys feature coarse grain boundary intermetallic particles in their as-produced state, which may interfere with or exacerbate the localized stresses near the impingement site, leading to changes in the likelihood of transmission. A combination of Crystal Plasticity - Fast Fourier Transform modeling and EDS-EBSD is used to analyze instances of twinning and twin transmission near grain boundary particles in Mg alloys to determine how particle morphology, position, and grain orientation modify twinning behavior.
Water Adsorption and Surface Atom Dissolution on Zn, Al, Ce Doped Mg Surfaces: Qin Pang1; Miao Song1; Rajib Kalsar1; Vineet Joshi1; Peter Sushko1; 1Pacific Northwest National Laboratory
In the current work, we investigate the role of Al, Zn and Ce elements in the initial stages of water adsorption on Mg surfaces and surface dissolution at the atomic scale. Density functional theory simulations reveal noticeable charge transfer between surface Mg and dopants, which affects energetics and configurations of the water adsorption. Water molecules are more stable on Mg sites near Zn and Al than on the pure Mg surface; the adsorption energies are even larger on the Mg sites close to two dopants on co-doped surfaces. However, the Ce site on the Ce-doped surface is the most stable site for adsorption of water. On clean surfaces, dopants decrease the stability of neighboring Mg atoms; with the notable exception of Zn, these dopants are more stable at the surface than the host Mg atoms. The effect of adsorbed water on the dissolution of surface atoms will be discussed.