Magnesium Technology 2020: Corrosion
Sponsored by: TMS Light Metals Division, TMS: Magnesium Committee
Program Organizers: J. Brian Jordon, Baylor University; Victoria Miller, University of Florida; Vineet Joshi, Pacific Northwest National Laboratory; Neale Neelameggham, IND LLC
Wednesday 2:00 PM
February 26, 2020
Room: 6C
Location: San Diego Convention Ctr
Session Chair: Bin Li, University of Nevada; Domonkos Tolnai, Helmholtz-Zentrum Geesthacht
2:00 PM Invited
Anomalous Hydrogen Evolution on Magnesium: Aline Gabbardo1; Gerald Frankel2; 1Ohio State Univ; 2Ohio State University
When Mg undergoes anodic polarization in a corrosive environment, the rate of hydrogen evolution (HE) increases with increasing applied anodic potential or current, which is opposite of the expected behavior based on standard electrochemical kinetics. This anomalous HE has been the recent focus of researchers worldwide. In this work, the behavior of sputtered Mg thin films and scratched Mg electrodes is presented. HE vanished when the potential of a pit in Mg thin films was increased into the region where a salt film formed. The peak anodic current on scratched samples was not anomalous, as it decreased slightly with increased potential. These observations indicate that the HE rate on Mg depends on the nature of the surface and that anomalous HE results from the surface being more catalytic to the HE reaction with increasing dissolution rate.
2:30 PM
Numerical Investigation of Micro-galvanic Corrosion in Mg Alloys: Role of the Cathodic Intermetallic Phase Size and Spatial Distributions: Vikrant Beura1; Pulkit Garg1; Vineet Joshi2; Kiran Solanki1; 1Arizona State University; 2Pacific Northwest National Laboratory
Magnesium alloys are of increasing interest due to their low-density, moderate specific strength and stiffness, recyclability, and high damping among other properties. However, the wide-scale applicability of magnesium alloys in structural applications have been limited due to many factors including its poor corrosion resistance. In this work, a numerical investigation examining the influence of cathodic intermetallic phase (β-Mg17Al12) size and spacing distributions in a Mg matrix was carried out to simulate the micro-galvanic corrosion behavior. The ratio of cathodic to anodic surface area was kept constant in each run to understand the effect of size and spacing distributions. In general, fragmentation of a larger intermetallic into smaller ones was found to enhance the localized current density. However, the uniform distribution of this small intermetallic phase throughout the matrix was found to reduce the overall dissolution current density and hence pitting corrosion severity.
2:50 PM Cancelled
The Corrosion Behavior of High Purity Mg According to Process History: Sangkyu Woo1; Byeong-Chan Suh2; Nam Ryong Kim1; Ha Sik Kim2; Chang Dong Yim2; 1University of Science and Technology; 2Korea Institute of Materials Science
In this study, we paid attention on the big difference between the corrosion rates of permanent mold cast and hot-extruded pure Mg. Fe existed as different state according to process history, which affected the corrosion behavior of pure Mg largely. The corrosion rate of high purity Mg was measured extremely low when Fe was dissolved into the matrix as a solid solution while it increased dramatically when Fe was precipitated as a secondary phase. The precipitation behavior of the secondary phase containing Fe was affected by other impurities as much as thermal history, which affected the corrosion behavior of high purity Mg. It is suggested from this study that the tolerance limit of Fe is strongly dependent on the content of Fe, the sort and content of other impurities and process history, which should be considered to design the composition and processing route of high corrosion-resistant Mg alloy.
3:10 PM
Effect of 2 wt % Ag Addition on Corrosion Properties of ZK40 for Biodegradable Applications: Marwa AbdelGawad1; Bilal Mansoor1; Matthew Vaughan2; Ibrahim Karaman2; 1Texas A&M University At Qatar; 2Texas A&M University
The antibacterial effects of silver make it an attractive alloying element for biodegradeable Mg alloys to treat possible inflammation and infections caused by the degrading orthopedic implants. In this study, as-extruded Mg-4%Zn-0.5%Zr (ZK40) alloy was alloyed with Ag, specifically 2 wt%, and subjected to a heat treatment at 350 °C for 7 days. The mechanical and corrosion response were studied in two orthogonal planes before and after silver addition to explore its potential for biodegradable orthopedic applications. Corrosion characteristics were assessed at 37 °C in Hank’s solution for 24 hours via electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PD) and open circuit potential (OCP). As-extruded and heat-treated ZK40 alloy displayed an inhomogeneous microstructure containing large, coarse grains, Zn-Zr rich secondary phase and some fine grain regions. While in ZK40-Ag, both planes showed a relatively more homologous microstructure but with some agglomeration of Zn-Ag rich secondary phases. Here, we present our initial results on the different corrosion behaviors observed in the two materials.
3:30 PM Break
3:50 PM
Design of the Magnesium Composite with High Corrosion Resistance and High Deformability: Yuecun Wang1; Boyu Liu1; Zhiwei Shan1; 1Center for Advancing Materials Performance from the Nanoscale, Xian Jiaotong University
Despite their energy-efficient merits as promising light-weight structural materials, magnesium (Mg) based alloys suffer from inadequate corrosion resistance. One primary reason is that the native surface film on Mg formed in air mainly consists of Mg(OH)2 and MgO, which is porous and unprotective, especially in humid environment. Here, we demonstrate an environmentally-benign method to grow protective film on the surface of Mg /Mg alloy samples at room temperature, via a direct reaction of already-existing surface film with excited CO2. Moreover, for samples that have been corroded obviously on surface, the corrosion products can be converted directly to create a new protective surface. Mechanical tests show that compared with untreated samples, the protective layer can elevate the yield stress, suppress plastic instability and prolong compressive strains without peeling off from the metal surface. This environment-friendly surface treatment method is promising to protect Mg alloys, including those already-corroded on the surface.
4:10 PM
Corrosion Behavior of Squeeze Cast Mg Alloy AM60-based Hybrid Nanocomposite: Hongfa Hu1; 1University of Windsor
Micron-sized alumina (Al2O3) short fibre and/or nano-sized alumina (Al2O3) particles were squeeze cast into Mg AM60 alloy. Two types of 7 vol.% Fibre/ AM60, and (7 vol. % Fibre + 3 vol.% nano-Particle)/AM60 composites, as well as the unreinforced matrix alloy were prepared. The corrosion behaviors of the composites as well as the unreinforced matrix alloy were investigated by using the potential-dynamic polarization test. Compared with the matrix alloy, the introduction of micron-sized alumina fibres decreased the corrosion resistance of Mg alloy AM60 considerably due to the presence of excessive interfaces between the fibre and matrix. The high density of grain boundaries and the absence of noble precipitates such as β-Mg17Al12 phases and Al-Mn intermetallics at the grain boundaries in the composites should be for the reduction in their corrosion resistance. The addition of the nano-sized particles led to almost no further reduction in the corrosion resistance of the composite.
4:30 PM
Al8Mn5 Particle Clustering on Oxide Films in Liquid AZ80 Magnesium Alloys: Liuqing Peng1; Te-Cheng Su1; Kazuhiro Nogita2; Hideyuki Yasuda3; Christopher Gourlay1; 1Imperial College London; 2The University of Queensland; 3Kyoto University
Al8Mn5 particles are important for ensuring adequate corrosion resistance of Mg-Al-based alloys. However, excessive Al8Mn5 formation above the Mg liquidus temperature can lead to sludge formation, and the clustering of Al8Mn5 particles on oxide films can generate deleterious casting defects, particularly in direct chill cast ingots. Here, we use real- time synchrotron X-ray radiography to study Al8Mn5 particle settling, the formation of a sludge layer, and the mechanism of Al8Mn5 clustering on oxides in AZ80 containing two Fe levels. It is shown that settling Al8Mn5 can become trapped in entrained oxide and continue to grow, creating large Al8Mn5 clusters
4:50 PM
Study of In-vitro Biodegradation Behavior of Mg-2.5Zn-xES Composite: Srinivasan Murugan1; Paul Okonkwo1; Ahmed Bahgat2; Gururaj Parande3; Aboubakr M. Abdullah2; Manoj Gupta3; 1Dhofar University; 2Qatar University; 3National University of Singapore
In this study, zinc (Zn) and eggshell (ES) reinforced biodegradable magnesium alloy (Mg-2.5Zn) and environment concise (eco) composite (Mg-2.5Zn-xES) was fabricated using disintegrated melt deposition (DMD) technique. In vitro experiments were conducted to study the biodegradation behavior of Mg-2.5Zn and Mg-2.5Zn-xES (x = 3 and 7 wt%) using simulated body fluid (SBF) under standard human body temperature of 37 °C. Using electrochemical Impedance Spectroscopy (EIS), electrochemical analysis was performed to study in vitro degradation behavior of alloy and composite. EIS revealed increased in vitro degradation of the biodegradable magnesium alloy and ecofriendly composite as percentage of ES reinforcement was increased. X-ray diffraction (XRD) was performed to observe the chemical composition of elements and reaction products present in the degraded samples after corrosion process. Scanning electron microscopy (SEM) analysis showed variations in surface morphology of the alloy and composite before and after degradation. SEM result revealed presence of defects in the tested samples after degradation process.