Magnesium Technology 2016

PREFACE

It is our great pleasure to bring you this volume of Magnesium Technology 2016, which is the proceedings of the Magnesium Technology Symposium held at the 145th TMS Annual Meeting & Exhibition in Nashville, Tennessee, February 14–18, 2016. With contributions from 16 countries, representing the latest trends in the eld of magnesium research, this volume can be regarded as a central repository of the nest research carried out in magnesium technology from around the world. With the tradition of presenting the most recent and highest quality work, all presenters have submitted their work to this edited proceedings volume or other peer reviewed TMS journals. All papers included in this volume were peer reviewed by the best possible experts in the concerned elds of magnesium research. The reviewers' contribution continues to be important to the success of this symposium. These contributions were presented in 9 sessions including a plenary session. Extended abstracts of the six keynote lectures given in the plenary session are also included here.

Going by the current trends, the contributions are classi ed into primary production and recycling, solidi cation and casting, alloy development, joining (welding) and diffusion, magnesium–rare-earth alloys, long period stacking ordered (LPSO) alloys and composites, twinning and plasticity, texture and formability, and corrosion. Challenges to improve plasticity and formability continue to excite researchers; most contributions deal with twinning, dislocation slip and texture. A fairly large number of contributions deal with the improvement of properties by the addition of rare-earth elements, investigating different aspects. Alloys forming the LPSO phase are also a part of this effort. Efforts are also seen in the areas of joining and corrosion, which are crucial for the application of magnesium alloys. Primary production, recycling and solidi cation remain as important as ever.

Over the years, a vast amount of scienti c insights have been gained into magnesium and its alloys from various perspectives, as witnessed in the volumes of Magnesium Technology. How to put all this expertise into practical applications and commercialization is the main focus of the plenary session this year. The talk by Martyn Alderman (Magnesium Elektron), who has years of experience in industry and R&D, examines A Perspective: Potential Growth in the Global Magnesium Industry–Where Is Our Research Leading Us? Karl U. Kainer (MagIC – Helmholtz Zentrum Geesthacht), a well-known leader in magnesium research, looks at Challenges for Implementation of Magnesium into More Applications. An extensive and critical application of magnesium alloys has come up in high speed trains in China. Given the large network of these trains in China, to be potentially followed in other countries, this is a large scale application. This will be discussed by Eric Nyberg (Paci c Northwest National Laboratory). South Korea has been in the forefront of innovations for applications of magnesium alloys. Nack J. Kim (Pohang University of Science and Technology) will tell us about this in his talk entitled Korea's R&D Activities Towards the Applications of Wrought Mg Alloys. Many of the intermetallic phases used in the strengthening of magnesium alloys have very fascinating structures, such as the quasicrystalline phase and the LPSO phase found in Mg-Zn-RE (rare-earth) alloys. LPSO phase magnesium alloys have attracted much attention in the past several years. Eiji Abe (University of Tokyo) will talk about Fascinating LPSO-structured Mg Alloys. Issues of plasticity and other aspects can be skirted by making the matrix amorphous, instead of crystalline, as described by Kevin Laws (University of New South Wales) in his talk The Developments in the High Magnesium Content Bulk Metallic Glasses and Future Possibilities. In parallel, two specialized symposia are being held, one on Magnesium-based Biodegradable Implants, being co-sponsored by (TMS) Functional Materials Division, Light Metals Division, Structural Materials Division, Biomaterials Committee and our own Magnesium Committee, and another on Strip Casting of Light Metals (second in the series, following last year's success), co-sponsored by Aluminum Committee and Magnesium Committee. Organized by Wim Sillekens (European Space Agency), Martyn Alderman (Magnesium Elektron), Patrick K. Bowen (Michigan Technological University), Jaroslaw Drelich (Michigan Technological University), and Petra Maier (University of Applied Sciences, Stralsund), 16 presentations will be made in the biodegradable implants symposium. The written accounts of eleven of them appear in this volume, while the other five are scheduled for publication in the April 2016 Issue of JOM. There are also three manuscripts from the Strip Casting of Light Metals Symposium, which is organized by Kai F. Karhausen (Hydro Aluminium Rolled Products GmbH), Dietmar Letzig (MagIC – Helmholtz Zentrum Geesthacht), Jan Bohlen (MagIC – Helmholtz Zentrum Geesthacht), and Murat Dundar (Assan Aluminium).

We would like to gratefully acknowledge and thank all authors for contributing to the symposium and this volume with their high-quality work, reviewers who put in their best efforts to ensure the quality of papers, plenary session speakers for giving their insights into current research and pointing to the future directions, session chairs, judges for posters, and everyone else who have volunteered to make this symposium a great success and in bringing out this high quality proceedings.

2016 Magnesium Technology Conference Organizers

Alok Singh, Chair

Kiran N. Solanki, Vice Chair

Michele V. Manuel, Past Chair

Neale R. Neelameghham, Advisor

ABOUT THE LEAD EDITOR

ALOK SINGH

MAGNESIUM TECHNOLOGY 2016 LEAD EDITOR

Alok Singh is a Chief Researcher in the Structural Materials Unit of National Institute for Materials Science in Tsukuba, Japan. He studied metallurgical engineering at undergraduate, masters and doctoral levels. He worked on kinetics of phase transformation in steels for his master's thesis at the Indian Institute of Technology at Kanpur. His Ph.D. work, at the Indian Institute of Science, was on the study of quasicrystalline and related intermetallic phases in aluminum alloys by transmission electron microscopy (TEM). He tackled the complex structures and reciprocal space of quasicrystals and its indexing problems.

Subsequently, he worked several years studying advanced materials by TEM at the Indira Gandhi Center for Atomic Research, and visited National Research Institute for Metals in Japan. He studied the effect of interfaces on melting and solidication of embedded nanoparticles. He has extensively studied the structure of interfaces between simple crystals and quasicrystals by TEM.

In 2002 he moved to his present working place National Institute for Materials Science and started working on magnesium alloys with special emphasis on Mg-Zn-RE alloys containing stable quasicrystal phase. His work has demonstrated very high strength with ductility in these alloys. These high mechanical properties have been analyzed with respect to microstructural characteristics. He has employed TEM to study dislocations, grain boundaries and twins, and interactions among these, to understand deformation behavior of magnesium alloys. Recently, he is applying advanced TEM techniques of scanning transmission electron microscopy (STEM) to study severely plastically deformed (SPD, a current trend in materials to achieve nano-scale microstructures) magnesium alloys, which is a challenge for the conventional TEM because of the strong contrast from the high amount of mechanical strain. He has over 90 refereed publications, over 30 contributions to proceedings, and several patents on magnesium alloys.

As a TMS member, he is a regular attendee of TMS annual meetings and has been involved with the Magnesium Committee for many years. He has been JOM representative and Vice Chair of the Magnesium Committee. He received the TMS Magnesium Fundamental Research Award for year 2009 along with his coworkers.

MAGNESIUM TECHNOLOGY 2016 EDITORS

Kiran Solanki is an Assistant Professor of Mechanical Engineering in the SEMTE at Arizona State University. Prior to coming to ASU, he was an Associate Director for the Center for Advanced Vehicular Systems at Mississippi State University. Dr. Solanki received his Ph.D. from Mississippi State University in December 2008. Dr. Solanki's research interest is at the interface of solid mechanics and material science, with a focus on characterizing and developing microstructure-based structure–property relationships across multiple length and time scales. To date, he has coauthored more than 50 journal articles, four book chapters, and more than 35 conference proceedings with faculty and students at ASU and MSU. In addition, his paper published in Engineering Fracture Mechanics was recognized as one of the most highly cited papers from year 2002 to 2005. For his efforts to promote the education of engineering students in the area of fatigue technology, he was awarded the SAE Henry O. Fuch Award by the SAE Fatigue Design & Evaluation Committee. In 2011, Dr. Solanki received the TMS Light etals Magnesium Best Fundamental Research Paper Award for his work on predicting deformation and failure behavior in magnesium alloys using a multiscale modeling approach. Recently, he received the 2013 TMS Light Metals Division Young Leader Professional Development Award, the 2013 Air Force Of ce of Scienti c Research Young Investigator Research Award, and the 2013 ASME Orr Award for Early Career Excellence in Fatigue, Fracture, and Creep.

Michele V. Manuel is an Associate Professor in the Department of Materials Science and Engineering at the University of Florida. She received her Ph.D in Materials Science and Engineering at Northwestern University in 2007 and a B.S. in Materials Science and Engineering at the University of Florida in 2002. Prior to arriving at the University of Florida, she performed her postdoctoral work at the General Motors Technical Center in Warren, Michigan. She is the recipient of the NSF CAREER, NASA Early Career Faculty, ASM Bradley Stoughton Award for Young Teachers, AVS Recognition for Excellence in Leadership, TMS Early Career Faculty, TMS Young Leader Professional Development, and TMS/JIM International Scholar awards. Her research lies in the basic understanding of the relationship between processing, structure, properties, and performance. She uses a systems-based materials design approach that couples experimental research with theory and mechanistic modeling for the accelerated development of materials. Her current research is focused on the use of systems-level design methods to advance the development of new materials through microstructure optimization. In the TMS Magnesium Committee, she has previously served in the roles of Chair, Vice-Chair, Secretary, JOM Advisor, JOM Advisor in Training, and currently serves in the position as the Past Chair. Additionally, she serves as the Vice-Chair on the Content Development and Dissemination Committee, as wellas a member of the Education, Young Leaders, Integrated Computational Materials Engineering (ICME), Biomaterials, and the Women in Science Committees.

Neale R. Neelameggham is ‘The Guru’ at IND LLC, involved in technology marketing and international consulting in the eld of light metals and associated chemicals (boron, magnesium, titanium, lithium, and alkali metals), rare earth elements, battery and energy technologies, etc. He was a visiting expert at Beihang University of Aeronautics and Astronautics, Beijing, China. He was a plenary speaker at the Light Metal Symposium in South Africa – on low carbon dioxide emission processes for magnesium.

He has over 38 years of expertise in magnesium production and was involved in process development of its startup company NL Magnesium through to the present US Magnesium LLC, UT from where he retired in 2011. He is developing thiometallurgical processes – a new concept of using sulfur as the reductant and/or fuel. He has published a heat transfer model for global anthropogenic warming based on thermal emissions independent of energy conversion source.

Dr. Neelameggham holds 16 patents and patent applications, and has published several technical papers. He has served in the Magnesium Committee of LMD since its inception in 2000, chaired it in 2005, and in 2007 he was made a permanent co-organizer for the Magnesium Symposium. He has been a member of the Reactive Metals Committee, Recycling Committee, Titanium Committee, and Programming Committee Representative of LMD and the LMD Council.

Dr. Neelameggham was the inaugural chair, when in 2008, LMD and EPD created the Energy Committee, and has been a co-organizer of the Energy Technology symposium through the present. He received the LMD Distinguished Service Award in 2010. While he was the chair of Hydro- and Electrometallurgy Committee he initated Rare Metal Technology symposium in 2014. He is co-organizer for the 2016 symposia on Magnesium Technology, Energy Technology, Rare Metal Technology and light metals section of REWAS 2016.

MAGNESIUM-BASED BIODEGRADABLE IMPLANTS 2016 EDITORS

Wim H. Sillekens is a project manager in the Strategic & Emerging Technologies Team at the research and technology center of the European Space Agency (ESA–ESTEC), where he is currently acting as the coordinator of the European Community research project ExoMet. He obtained his Ph.D. from Eindhoven University of Technology, Netherlands, on a subject relating to metal-forming technology. Since that time he has been engaged in aluminum and magnesium research, amongst others on (hydro-mechanical) forming, recycling/rening, (hydrostatic) extrusion, forging, magnesium-based biodegradable implants, and as of late on light-metal-matrix nanocomposites. His professional career includes positions as a post-doc researcher at his alma mater and as a research scientist/project leader at the Netherlands Organization for Applied Scientic Research (TNO). International working experience covers a placement as a research fellow at MEL (now AIST) in Tsukuba, Japan, and – more recently – shorter stays as a visiting scientist at GKSS (now HZG) in Geesthacht, Germany, and at Paci c Northwest National Laboratory (PNNL) in Richland WA, USA. He has (co)-authored a dissertation, book chapters, journal papers, patents, conference papers, (keynote/invited/contributed) oral presentations, and so on (about 150 entries to date). Other professional activities include an involvement in association activities (amongst others, as the lead organizer of TMS Magnesium Technology 2011), international conference committees, and as a peer reviewer of paper manuscripts for scienti c journals and conference proceedings as well as of research proposals. Research interests are in physical and mechanical metallurgy in general and in light-metals technology in particular.

Martyn Alderman is Divisional Director of Technology for the Magnesium Elektron Group Worldwide. He obtained a Masters Degree in Material Science from the University of Cambridge (United Kingdom) in 1979 and for the next twenty years he worked in aluminum rolling mills producing and developing Al-Cu-Zr, Al-Mn, Al Mg-Mn, Al-Zn-Mg, and Al-Li-Cu alloys for superplastic forming. He also has signi cant operational experience in direct chill casting and in the extrusion of high strength aluminum alloys.

In 2003 he joined Magnesium Elektron during the acquisition of their large Madison, Illinois rolling operation in the USA. For the next few years he travelled between the USA and Europe encouraging the wider use of magnesium sheet in transport applications, in particular by use of superplastic forming, and later in managing the post acquisition integration of the Revere North American Graphic Arts business. He chaired the 2010 and 2015 International Magnesium Association Conferences in Hong Kong and Vancouver, WA, USA, and in 2011–2012 was involved in editing and producing a 270 page Handbook on Designing with Magnesium Alloys.

More recently he has been involved in a U.K. Technology Strategy Board Project aimed at the Design of a Magnesium Intensive Vehicle in conjunction with the Morgan Motor Company; as an advisor to the International Magnesium Association Life Cycle Study on automotive and aerospace applications; and in a National Aerospace Technology Exploitation Programme focused on improving buy to y ratios in magnesium aircraft seat components.

As a member of TMS, SAE and AMS, he is a regular attendee at worldwide magnesium conferences keeping abreast of global technology development with the aim of maintaining Magnesium Elektron's position as a world leader in magnesium alloys and their end use including biomedical applications; during 2016 he will again be chairing the International Magnesium Association Conference in Rome.

Patrick K. Bowen studied Materials Science and Engineering at Michigan Technological University, receiving his B.S. in 2011, and his Ph.D. in 2015. His research has spanned a wide array of topics—from archaeometric studies on ceramic artifacts, to magnesium biocorrosion kinetics and mechanism, to the application of zinc in bioabsorbable materials applications. He has published nearly twenty articles in peer-reviewed journals since 2011 with more than 230 combined citations, and he has been an active member of TMS since 2010 and a member of the Biomaterials Committee since 2013. He will begin employment as a Senior Research Metallurgist with Deringer-Ney, Inc. (Bloom eld, Connecticut) beginning in January 2016.

Jaroslaw W. Drelich received his B.S. degree in chemistry and M.S. degree in chemical technology from the Technical University of Gdansk (TUG), Poland, in 1983, and earned his Ph.D. degree in metallurgical engineering from the University of Utah in 1993. He came to Michigan Technological University (Michigan Tech) in 1997 and currently is a professor of materials science and engineering. His main research interests are in applied surface chemistry and interfacial engineering for ore dressing and materials processing, materials characterization, formulation, modication and testing of biomaterials and antimicrobial materials. In the last few years, Dr. Drelich's research focused on bioabsorbable implant materials including magnesium, and he is coinventor of a new class of biodegradable zinc-based materials for vascular stent applications. Aside from teaching several courses on characterization and processing of materials at Michigan Tech, Dr. Drelich has edited six books, published more than 170 technical papers (cited nearly 4,000 times according to Google Scholar), holds nine patents and has more than 50 conference presentations, including several keynote addresses, to his credit.

Dr. Drelich is the Editor-in-Chief for the Surface Innovations journal. He is the active member of The Minerals, Metals & Materials Society (TMS), Society for Mining, Metallurgy and Exploration (SME), and American Chemical Society (ACS), and has served on a number of different committees; currently, he serves as Past-Chair for the TMS Energy Committee. Dr. Drelich is also an advocate of interdisciplinary capstone senior design projects, and promotes interdisciplinary projects between engineering and business to encourage the students to think about both technical and business viability and interconnections. In recognition of his entrepreneurial activities, Dr. Drelich has been awarded with the 2012 Food Safety Innovation Award from Great Lakes Entrepreneur's Quest in Michigan.

Petra Maier received her doctoral degree from Loughborough University, U.K. in 2002 in Materials Science, especially in the eld of grain boundary segregation in steel. After completing her Ph.D. she worked at the University of Applied Sciences Wildau in Germany as a postdoctoral fellow under supervision of Prof. Asta Richter with a focus on microhardness measurements by nanoindentation. From 2004 to 2006 she worked as a research associate at the Helmholtz Zentrum Geesthacht in Germany in the Institute of Materials Research led by Prof. Karl Ulrich Kainer, responsible for the operational division Magnesium Innovation Centre. In the group of Dr. Norbert Hort, she worked in the area of Magnesium recycling and high temperature alloy development. From 2006 to 2008 Petra Maier was a research associate at the Technical University Berlin in Germany in the Institute of Material Sciences and Technologies, Department of Materials Engineering of Prof. Claudia Fleck. There, her research specialities included corrosion fatigue on magnesium. Since 2008 Petra Maier has been a Professor of Materials and Production Engineering in the School of Mechanical Engineering at the University of Applied Sciences Stralsund in Germany. She enjoys working in the eld of magnesium-based biodegradable implants. Her research interests are focused on corrosion under stress and crack propagation in uenced by the microstructure. The current research relates to investigating innovative magnesium–rare-earth alloys in the form of wires, with a possible application as pins, rods, and clips for the temporary xation of bone fracture or for forming stents.

STRIP CASTING OF LIGHT METALS 2016 EDITORS

Kai F. Karhausen is head of the research department Rolling Technology at the R&D Centre of Hydro Aluminium Rolled Products GmbH in Bonn, Germany. He graduated in 1994 with a Ph.D. in Materials Science from the University of Technology RWTH Aachen. He joined the Hydro Aluminium R&D Centre in KarmØy, Norway and conducted research in the field of aluminum extrusion before moving to the R&D Centre in Bonn to work on the rolling technology of aluminum. He is the author of a large number of papers with a focus on metal forming technology, numerical simulation, and integration of material models into process simulation tools. He served as chair of the Aluminum Processing Committee of TMS for five years.

Dietmar Letzig is head of the Wrought Magnesium Alloys Department at the Magnesium Innovation Centre of the Helmholtz Zentrum Geesthacht in Germany. He is the author of many papers in peer-reviewed scientic journals and proceedings of international conferences. His area of expertise is microstructure and mechanical properties of wrought magnesium alloys processed by severe production processes. He is leading fundamental as well as application-oriented research projects in metal forming processes and an expert in the processing of magnesium sheet including twin roll casting and the optimisation of the magnesium sheet performance.

Jan Bohlen is a research scientist with the Magnesium Innovation Centre (MagIC) at the Helmholtz-Zentrum Geesthacht in Germany. He graduated in Material Physics in 1996 and obtained his Ph.D from the University of Göttingen (Germany) in 2000. His work in the wrought magnesium alloys group at MagIC is focused on the development of new wrought magnesium alloys and understanding the effect of processing on microstructural development.

Murat Dündar holds the position of Director of Technology in Assan Aluminum. He joined Assan Aluminum in May 1999 as a research specialist. He has primarily focused on performance improvement of aluminum foil and sheet products produced out of Twin Roll Casting Technology (TRC), managing research and development projects on developing new alloys compatible with TRC technology, characterization of as-cast structures and related casting defects, interface between liquid metal and caster shell surface, solidi cation in TRC and related microstructures, tailoring microstructural features starting from casting and in further downstream operations, improvement in productivity of casting process and nally casting of high Mg-bearing and 6000 series alloys with TRC.

He holds a B.Sc. degree in Metallurgical Engineering from Middle East Technical University, Turkey, an M.Sc. degree in Materials Science from State University of New York at Buffalo, USA and a Ph.D. degree in Materials Engineering, from New Mexico Institute of Mining and Technology, USA.

MAGNESIUM TECHNOLOGY 2016

Session Chairs

Keynote Session

Alok Singh,

National Institute for

Materials Science

Kiran Solanki,

Arizona State University

Solidification and Casting

Norbert Hort,

MagIC – Helmholtz

Zentrum Geesthacht

Tracy Berman,

University of Michigan

Keynote Session Part II and

Primary Production and

Recycling

Neale R. Neelameggham,

IND LLC

Dmytro Orlov,

Lund University

Kiran Solanki,

Arizona State University

Alloy Development, Diffusion,

and Joining

Sean Agnew,

University of Virginia

Miroslav Sahul,

Slovak University of

Technology Bratislava

Magnesium-Rare Earth Alloys

Mark Easton,

RMIT University

Francesco D'Elia,

MagIC – Helmholtz

Zentrum Geesthacht

LPSO Alloys and Composites

Manoj Gupta,

National University of Singapore

Hyunkyu Lim,

Korea Institute of Technology

KITECH

Twinning and Plasticity

Tyrone Jones,

US Army Research Laboratory

Peifeng Li,

Nanyang Technological

University

Texture and Formability

Jan Bohlen,

MagIC – Helmholtz

Zentrum Geesthacht

Nitin Chandola,

University of Florida

Corrosion

Michele Viola Manuel,

University of Florida

MAGNESIUM-BASED

BIODEGRADABLE

IMPLANTS

Session Chairs

Materials and Processing /

Surface Modification and

Corrosion

Petra Maier,

Fachhochschule Stralsund

Jarek Drelich,

Michigan Technological University

Corrosion / Market and Clinic

Pat Bowen,

Michigan Technological University

Martyn Alderman,

Magnesium Elektron

STRIP CASTING

OF LIGHT METALS

Session Chairs

Strip Casting Process

Kai F. Karhausen,

Hydro Aluminium Rolled Products

Jan Bohlen,

MagIC – Helmholtz

Zentrum Geesthacht

Strip Casting: Properties

Murat Dundar,

Assan Aluminium

Dietmar Letzig

MagIC – Helmholtz

Zentrum Geesthacht

MAGNESIUM TECHNOLOGY 2016

Reviewer Pool

Magnesium

Technology

2016

SYMPOSIUM:

Magnesium

Technology 2016

Magnesium

Technology 2016

Keynote Session

CHALLENGES FOR IMPLEMENTATION OF MAGNESIUM INTO MORE APPLICATIONS

K.U. Kainer

Institute of Materials Research, Magnesium Innovation Center,

Helmholtz-Zentrum Geesthacht, Max-Planck-Straße 1, D-21502 Geesthacht, Germany

Abstract

As a result of the demands made on the transportation and the communication industries to introduce lighter materials, it is necessary to completely utilize the potentials of many different light structural materials. The different classes of light metal materials have to compete with each other as well as with polymers and steels. 200 years after its discovery magnesium is still one of the most promising materials for light weight constructions. Especially in the automotive industries the reduction of the weight of vehicles is a must. Car manufacturers have to decrease CO2 emissions in accordance to the legislation, especially that of the EU. Additionally, with the increasing fuel prices consumers expect a decrease in fuel consumption either by a decrease of vehicle weight or by increasing the engine efficiency. Mg alloys can contribute to both, especially in reduction in vehicle weight. Moreover Mg alloys can be fully recycled, which fulfils the requirements from the EU directive for the end of life of vehicles and also helps to lower the CO2 emissions associated with the processing of Mg.

Since the end of the last millennium, Mg alloys have made inroads into the applications in automotive industries as well as in consumer, computer and communication (3C) applications. Their favourable property profile – high specific strength, good machinability, recyclability – promote increased usage. Still, the full potential of Mg as a structural material has not been achieved. There a number of reasons can be specified:

Market issues: Price, protective duties, dependence on the Chinese Mg market, availability etc.

Reservation against Mg due to misinterpretation of properties: magnesium corrodes, magnesium burns etc.

Inadequate properties i.e. strength, ductility, corrosion behaviour, crash worthiness etc.

Limited number of suitable Mg alloys may restrict wider application of Mg alloys.

Life cycle assessment issues.

Despite magnesium alloys being in service for almost one hundred years, there is still a lack of knowledge potential of Mg alloys compared with other metallic materials such as steel or aluminium: Design, processing, potential etc.

Mg and its alloys face some specific obstacles in relation to its mechanical and physical properties that need to be addressed before wider application of Mg would be envisaged. Examples of properties of Mg that restrict the application of Mg include the flammability of the metal [1] with strong exothermic reaction, the poor formability especially at the room temperature [2] and the corrosion properties. Additionally, in classical forming processes such as machining, forming or surface protection require specific knowledge on how magnesium may be handled, e.g. handling and storage of Mg scrap from machining.

Flammability is not only an issue during casting of Mg alloys. It requires specific attention during any subsequent processing. Special measures should be considered during machining of the alloys and processing parameters must be adjusted with respect to the alloys used. There needs to be education on handling Mg during processing and subsequent use, e.g. automotive or aerospace require knowledge about handling Mg fire during service.

The specific nature of wrought Mg with its distinct microstructures and strong textures [3] requires adjustment of forming procedures during manufacturing. Engineering knowledge on handling of the specific needs of Mg needs to be developed. It is noteworthy that scientific and engineering knowledge on handling Mg is concurrently developed at present so that there is potential for direct interaction between scientific knowledge developed and the technical needs of application. Example of such concurrent development in knowledge is the formability of Mg alloys in form of forming limits, the applicability in form of forming faults as well as the resulting properties of the formed parts which have to meet the application requirements.

While all these issues can be overcome with the theoretical and technical knowledge on deformation of Mg, there is a broad distribution of knowledge on understanding the differences between Mg alloys and other metallic materials. It may be hypothesised that - being a metal - Mg and its alloys are prone to be misunderstood just as a metal, an issue which is not faced by other classes of materials such as reinforced polymers, plastics in general, wood, or textiles.

While the fundamental understanding on materials sciences are applicable for almost any metals and alloys, materials sciences and engineering classes often deal only with a limited number of materials. In terms of metallic materials steels are studied in detail as they form the basis of many structural applications. However, the exposure of students to other metals and alloys depend on the preference and education of the lecturer. Additionally text books are also written based on the interest and preferences of the author and therefore Mg often is not a topic in lectures any more than in text books which deal with metals and alloys. As a consequence engineers often do not know about Mg alloys and its advantages or has misleading information (Mg burns! This is from the science classes at secondary school, showing propagation of wrong or misrepresented information). The missing knowledge or wrong statements on Mg alloys contribute significantly to the prevention of their use.

When Mg alloys are compared with other materials often e.g. their mechanical properties are directly compared. However, this is like comparing an apple with an orange; both are round but have vastly different properties even though they are both fruit. A similar concept should also be applied for alloys e.g. for strength:

specific strength. In this case ultimate tensile strength (UTS) or yield tensile strength (YTS) are divided by the density of the alloy and the earth acceleration. The outcome would be a value with the dimension km. For UTS and YTS this would mean the length where the material fails or shows first plastic deformation under its own load. This concept can also be applied to Young’s modulus but would lead to more or less the same value for all metals and alloys. Applying this to engineering approaches would immediately show that Mg alloys would have advantageous properties in comparison with Al alloys and even steels.

Price is often also a determining factor in considering if a material is used or not. When comparing Al to Mg it could be shown that approximately the same amount of energy is necessary for the primary production, machining and recycling for both. However, Mg alloys perform better during casting and especially during use e.g. in automotive applications. Fuel savings (= less CO2 emissions) or an extended range are especially important for the consumer more than for the car manufacturers. Mg is still produced in much smaller quantities compared with other common alloys and therefore often more expensive. This in combination with non-existent knowledge on the properties and processing of Mg alloys contributes significantly to hindering the use of Mg alloys.

Since the interest in magnesium alloys for automotive application was reawakened in the middle of the 1990s, there is a rapid increase in the number of R&D activities on Mg alloys. Driven from the demands on Mg alloys for light structural application, research programs for the improvement in the property profile of Mg alloys and the development of production technology were launched. The research topics include fundamental and applied research with the aim to extend the potential use of magnesium components in different application sectors.

In the last 25 years the research on magnesium alloys and their technology escalated. Simple search shows the effect: Increase from about 408 papers per annum in 1990 to 2654 in 2014 [4]. In special topics such as magnesium biomaterials the number of papers has increased from about 2 in 1990 to more than 124 in 2014 [5]. The outcome from this research boom was a sustainable development magnesium technology through the development of new alloys and the development of advanced processes. The property profile of modern magnesium alloys shows a high potential for the increased use of magnesium in different application sections. To achieve this goal the dissemination of information on novelties, potential, property profiles and limitations of magnesium alloys is a necessary key factor. Conferences within the magnesium communities on magnesium alloys and their applications do not satisfy this demand. The proceedings from the biggest magnesium conference in 2015 for example contain more than 377 papers [6]. More than 53% of papers dealt with magnesium wrought materials which have a market share of less than 5%. Papers on cast alloys and casting processes only contributed to 14% of the papers and the important topic of corrosion and corrosion protection less than 10% of the total contributions. Design issues and consideration for applications are rarely discussed.

The biggest challenge for the Mg industry is the improvement of the visibility of Mg showing the high potential of Mg alloy as a potential light weight material. In commercially oriented conferences on lightweight materials Mg plays a minor role. Mg alloys are not even named as a potential lightweight material while aluminium, fibre reinforced polymers and even high performance steel are considered to be lightweight materials. In this sense Mg shows a shadowy existence. The Key factor for the improved visibility of Mg alloys is the education of designers, engineers and technicians on issues, challenges and potential of Mg alloys. Educational seminars, webinars, creating of data books and design guidelines together with revision of existing resource books [7] and textbooks and including complete and new information on Mg alloys and Mg alloy processing will provide an important contribution to extend the knowledge of Mg and its alloys and this will help with the visibility of Mg alloys leading and increased potential to introduce Mg into a wider range of applications.

DEVELOPMENT OF MAGNESIUM ALLOYS FOR HIGH SPEED TRAINS IN CHINA

Eric Nyberg¹, Jian Peng², Neale R. Neelameggham³

¹Pacific Northwest National Laboratory, Richland, WA, U.S.A.,

²Chongqing University, National Engineering Research Center for Magnesium Alloys, Chongqing, China, ³Ind LLC, Salt Lake City, UT, U.S.A.

Extended Abstract

In 1939, Dow Chemical had advertisements discussing the use of magnesium for trains, following their successful use of Dowmetal truck bodies in 1935. Despite the fact that the concept of using magnesium (Mg) alloys in trains has existed for at least 75 years, their remains significant challenges in alloy development and forming technologies before commercial application will find mass application.

In Dec. 2011, China Daily reported that a test bullet-train reached a world record-breaking speed of 500 km/hr (311 mph). Prior to this announcement, the fastest passenger train was the Beijing Shanghai High Speed Railway, operating at a top speed of 300 kilometers per hour. The new test train includes six passenger carriages, and the front end is tapered to a fine point, similar to (the) sharp edge of an ancient Chinese sword. The power of this train is 22,800 kilowatts and is constructed of lightweight plastic, magnesium alloy and reinforced with carbon fiber. Earlier versions of China Railway’s High-Speed (CRH) trains run at 9,600 kilowatts, with demonstrated speed of about 300 kmph (190 mph) [2].

A 2012 study indicated that use of ZK60A and AZ31B in seat back material in high speed trains will have a reduction in weight of 33% compared to the aluminum alloy seat back material [A7003-T5 or 5052] [3]. Although this may be an overly conservative estimate, because using Mg alloys may require engineering design with added strengthening features, it is still likely that more than 20% weight savings can be achieved compared to aluminum alloys. Similarly, when an aluminum alloy with Young's modulus of 70GPa was used to replace steel with a modulus of 210GPa, the train body and its components were redesigned to bear the vertical, lateral and torsional load. It should be expected that similar redesigns will be required when important structural parts of a train are substituted with Mg alloy having a Young's modulus not more than 45 GPa. Meanwhile,the main products used on high speed train are hollow, thin-wall extrusion profiles and sheet with thickness of approximately 4mm [4]. Additional efforts are still required to develop new alloys and advance manufacturing techniques to meet the demands of strength, straightness, flatness, corrosion resistance, and joining.

Gaofeng Quan, et al. described the use of Mg alloys will provide reduced vibration and noise in high speed trains - mainly by the superior damping capacity of magnesium alloys [5]. Such new alloys of high damping performance with associated high strength were developed in 2010 by Pan and Wang [6]. Such developments were made while continuing to push the limits for developing larger and larger magnesium alloy extrusion profiles. An additional advantage for using Mg alloys in high speed trains is its prominent ability to provide electromagnetic shielding [7], particular for the magnetic levitation trains, with the Mg alloy shielding the high intensity electromagnetic radiation produced when the trains start.

One of the Chinese patents shows the use of a magnesium alloy composite application as an air vent grill used in the high-speed trains and other vehicles. This composite is unique in using a magnesium structure with ribs covered on both the top and bottom with a rubber coating. This composite provides a high strength, impact resistant, light weight, sound, strong magnesium alloy composite structural panel [8]. Further Mg alloy applications in the demonstration train used forged ZK60 alloy for the frame, AZ31 sheet in the flooring, and extruded AZ31B profile for arm rests.[9]

Still today, the large-scale application of Mg alloy on trains is still in development. Some magnesium companies continue efforts to suplly samples to train manufacturing plants for assembly operational tests. In May 2015 Baosteel, China announced its entry into magnesium alloy market by a joint venture with BAIC Motor and Amgain Shandong Magnesium Co. with the main goal of providing components for transportation areas in automobile and rail transit [10]. Recently Amgain Shandong Magnesium Co. had provided about 50 large Mg alloy extrusion profiles for rail transit applications to Nanche Group and China CNR Corporation. Applications include stiffener or stringers with a weight of 7.5 kg, grills with a weight of 2.62 kg, and a baggage holder etc. The baggage holders had a fixed length of 7.5 meters, and could be produced up to 25 meters as needed [11]. The seat arm, reading lamp holder, seat frame, etc. were manufactured by Shandong Yinguang Yuyuan Light Metal Precise Forming Co., Ltd. Using semi-solid forming technology to produce a dense and refined microstructure with improved properties compared to similar die casting products [12]. The largest use of Mg alloys will likely come in the form of wrought alloy applications such as the structural stringers, seat frames and mounting profiles.

References:

[1] DowMetal –The Metal Travels Light, The Michigan Technic, vol 57 -58 May 1939.

[2] Tuan Nguyen, China Daily, Topic: Innovation, December 28, 2011.

[3] L. Song, Y. H. Zhao, J. Z. Liu, J. H. Mu, X. C. Guo, Study on the ZK60A and AZ31B Magnesium-Alloy in the Application on High-Speed Train Seats, Advanced Materials Research, Vols. 690-693, pp. 53-57, May. 2013.

[4] Li Rui-chun. Application and Development of Magnesium Used for High-speed Train. Railway Locomotive & Car, 2011, 31(6): pp. 59-62.

[5] Gaofeng Quan, Ruichum Li, Siu Gu and Zhaoming Liu, ‘Magnesium alloys- new materials for high-speed train with reduced vibration and noise", The 1st International Workshop on High-speed and Intercity Railways (IWHIR 2011), Yi-Qing Ni and Xiao-Wei Ye (Eds.),Shenzhen, July 2011. p 349-356.

[6] J.F.Wang, S.Gao, P.F.Song, X.F.Huang, Z.Z.Shi, F.S.Pan. J. Alloys Compd. 509 (2011) 8567-8572.

[7] Xianhua Chen, Lizi Liu, Juan Liu, Fusheng Pan. Microstructure, electromagnetic shielding effectiveness and mechanical properties of Mg Zn Y Zr alloys. Materials & Design, 2015, 65, pp 360-369.

[8] Chinese Patent, Magnesium alloy composite structural slab for high-speed trains and rail transit vehicles, CN 201971017 U. [9] May 2015 Press release by Baosteel, http://www.baosteel.com/group_en/contents/2863/78669.html Accessed 9/14/2015.

[10]http://www.rautomead.co.uk/158_Copper+Magnesium+Rod.html, Accessed 9/14/2015.

[11] Tianchang Huo. The application of magnesium alloy profiles in rail transit. The 17th annual meeting of magnesium industry session, 2014.

[12]Qianjin Wang. Application progress of high speed rail components with semi-solid casting. The 17th annual meeting of magnesium industry session, 2014.

KOREA’S R&D ACTIVITIES TOWARDS THE APPLICATION OF WROUGHT Mg ALLOYS

Nack J. Kim

Pohang University of Science and Technology (POSTECH); Pohang, Korea

Keywords: Magnesium alloys, alloy development, twin-roll casting, extrusion, applications.

Extended Abstract

Lightweighting of automobiles is possible through the application of materials such as advanced high strength steels and low density alloys including Al and Mg alloys. Among these, Mg alloys having a density about one-fourth of steel and two-thirds of Al can offer greater weight reduction over other materials, provided that Mg alloys have comparable mechanical properties to those of steels and Al alloys. Due to their advantage of being the lightest structural alloys, the use of large amounts of Mg alloys in automobiles has been frequently predicted, but their actual application, particularly of wrought products, in automobiles is quite limited. Such limited application of wrought Mg alloys has been mainly due to their several shortcomings such as high cost, poor mechanical properties including formability, poor corrosion resistance, etc. The widespread application of wrought Mg alloys in automobiles depends on how these challenges are addressed. At present, several countries are actively pursuing the R&D to overcome these challenges and the present talk discusses the Korea's R&D activities towards the applications of wrought Mg alloys.

Fig. 1. Schematic diagram showing the Mg-WPM project.

The major R&D project on Mg alloys in Korea is the so-called Mg materials R&D project for the super-light vehicles, a part of the World Premier Materials (WPM) program. Led by POSCO, it started in 2010 (until 2019 for a duration of 9 years) and 28 organizations are currently involved in the project, including 3 automotive makers, 14 automotive component manufacturers, 7 universities, and 4 research institutes. The project consists of 2 sub-projects; sheet products and bulk products as schematically shown in Fig. 1.

The sub-project on sheet products is aimed at developing low cost, high strength and high formability Mg alloy sheets and deals with various aspects of Mg alloy sheet productions and applications such as the development of efficient smelting technology, new alloy developments, hot/warm coil rolling process, forming, joining and surface treatments. The key part of this sub-project is the utilization of twin-roll casting (TRC) process, which allows the continuous fabrication of thin sheet products and therefore improves productivity and reduces the cost associated with sheet production. TRC process also gives several metallurgical benefits to the alloys such as refinement of microstructural constituent phases, allowing the development of novel alloys utilizing alloying elements that have limited solid solubilities in Mg. Utilizing TRC, several conventional alloys such as AZ, ZK, and AM series alloys have been fabricated and new alloy systems have also been developed with improved tensile properties and formability, Some of these alloys have found application in automobiles and are currently being used in several automobiles including the Porsche 911, Renault-Samsung SM7, and Renault’s concept car, Eolab. POSCO’s Mg plant boasts a 2,000 mm wide twin-roll caster and a few 600 mm wide twin-roll caster, along with tandem rolling mill.

The second sub-project on bulk products is aimed at developing high strength Mg alloys and related processes with improved productivity. Similar to the sub-project on sheet products, it deals with new alloy development and process design for extrusions, forgings and castings. Regarding the extrusions, the main emphases have been placed on developing high strength extrusion alloys that can be extruded at a fast extrusion speed as well as ultra-high strength extrusion alloys. One of the developed alloys can be extruded at an extrusion speed of 24 m/min without forming any surface defects. Another alloy system shows tensile strength of ~ 450 MPa and elongation of ~ 13% and more importantly does not show tension-compression anisotropy. These alloys have been successfully forged into various automotive parts such as arm, link, and bumper.

Although not supported by the WPM program, there are several other programs on Mg alloys in Korea. One of them is the development of non-flammable Mg alloys with both excellent mechanical properties and ignition/corrosion resistance, led by the scientists at the Korea Institute of Materials Science. They showed that the combined addition of Ca and Y leads to significant improvements in non-flammability and tensile properties, compared to conventional Ca containing Mg alloys. These alloys also have better corrosion resistance than any other commercial alloys or Ca containing alloys

This talk will summarize the current R&D efforts on Mg alloys in Korea and will provide an insight on future R&D directions for commercialization of Mg alloys.

Acknowledgements

This work was supported by the WPM Program funded by the Ministry of Industry, Trade and Energy, Korea. The author would like to thank all the participants of the program.

FASCINATING LPSO-STRUCTURED Mg ALLOYS

Eiji Abe

Department of Materials Science & Engineering, University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan

Keywords: Mg alloys, Structure, Phase stability, First-principles calculations, Electron Microscopy

Recent successful alloy-design showed that Mg alloys with addition of a small amount of Zn and Y (or rare-earth elements) reveal excellent mechanical properties including remarkably improved strength with a reasonable ductility [1,2]. One of the prominent microstructural features, which are believed to contribute for these excellent properties, is formation of a novel type of long-period structures [3-6]. The structures arefundamentally long-period stacking derivatives of a hexagonal close-packed structure (hcp-Mg), and the resultant stacking polytypes accompany a unique chemical order that occurs to synchronize with the corresponding stacking order; i.e., the synchronized long-period stacking/order (LPSO) structure (Fig.1) [5].

Fig.1 Z-contrast STEM images and model structures of a series of synchro-LPSO crysatals; (a) hcp-Mg, (b) 10H, (c) 18R, (d) 14H, and (e) 24R (adapted from ref. 5).

Fig.2 Local Zn-Y configurations before (left) and after (right) the energetic relaxations (adapted from ref. 6).

LPSO-structured ternary Mg-TM-RE (TM: transition metals, RE: rare-earth elements and Y) alloys reveal remarkable performance even at elevated temperatures, providing an extended opportunity for various applications. To accelerate further developments of the alloys, understanding their thermodynamic stability becomes important. With this aim, we have attempted to evaluate phase stability as well as to construct model structures of the complex LPSO crystals, based on the-state-of-the-art electron microscopy and first-principles calculations. It has become apparent that the ordered characteristics of the LPSO structures are well represented by the TM6RE8 clusters with a L12-type configuration. Interestingly, significant displacements occur for the Zn6Y8 clusters after energetic relaxations (Fig.2) [6], causing generations of internal ‘voids’ at the cluster centers, which are sufficiently capable for incorporating an extra atom as interstitials. Introduction of such interstitials (I) into the close-packed LPSO structures turns out to increase remarkably the thermodynamic stability for several LPSO-Mg alloys [7]. These theoretical predictions have been experimentally verified with the aid of a novel ultrahigh-sensitive electron microscopy imaging [8] and. convergent-beam electron diffraction (CBED) analysis, leading to a conclusion that Mg atoms indeed exist at the relaxation-induced I-sites in the several LPSO-Mg alloys. We believe that the present results provide an interesting interstitial-aided stability mechanism. We will also describe several LPSO-related structures identified in ternary Mg-TM-RE alloys, including unique zones similar to those frequently observed in Al-TM alloys (i.e., GP zones).

References

[1] Y. Kawamura et al, Mater. Trans. 42 (2001) 1172.

[2] Y. Kawamura, M. Yamasaki, Mater. Trans. 48 (2007) 2986.

[3] E. Abe et al, Acta Mater. 50 (2002) 3845.

[4] Y. M. Zhu, A. J. Morton, J. F. Nie, Acta Mater. 58 (2010)2936.

[5] E. Abe et al, Philos. Mag. Lett. 91 (2011) 690.

[6] D. Egusa, E. Abe, Acta Mater. 60 (2012) 166.

[7] J. E. Saal et al. Acta Mater. 68 (2014) 325.

[8] R. Ishikawa et al., Nature Mater. 10 (2011) 278

DEVELOPMENTS IN HIGH MAGNESIUM-CONTENT BULK METALLIC GLASSES AND FUTURE POSSIBILITIES

Kevin J. Laws, Karl F. Shamlaye, Jörg F Löffler, Michael Ferry

¹School of Materials Science and Engineering, UNSW, Sydney, NSW 2052, Australia

² Laboratory of Metal Physics and Technology, Department of Materials, ETH Zurich, 8093 Zurich, Switzerland

Keywords: Bulk Metallic Glass, Amorphous Alloys, Magnesium Alloys

Abstract

Amorphous alloys or metallic glasses have been earmarked as the most significant development in materials science since the discovery of plastics over 50 years ago (Mike Ashby, 2011) and are gaining significant attraction as ‘ Next Generation’ materials [1].

When compared to crystalline alloys, amorphous alloys possess superior strengths (approximately three-times that of their crystalline counter-parts), which approach the theoretical strength maximum [1], the highest elastic limits of all metallic materials (at least twice that of regular metals), improved corrosion resistance, and amorphous alloys based on palladium exhibit the highest damage-tolerance of all materials known [1,2]. Unlike crystalline metal alloys, metallic glasses exhibit a glass transition temperature, above which the alloy exists in a ‘super-cooled liquid’ state, where viscosity or flow stress is reduced by several orders of magnitude. Here, superplastic forming techniques (similar to plastics and ceramic glasses) such as forging, extrusion, drawing and blow moulding can be performed [3].

Magnesium alloys exhibit the lowest density of all engineering materials and continue to play an increasingly significant role in aerospace, automotive, consumer electronics and biomedical applications as a result of their high specific strength, stiffness and biocompatibility. Since the discovery of the Mg70Zn30 metallic glass in 1977 [4], numerous Mg-based amorphous alloys or ‘bulk’ metallic glasses have been developed. Due to ideal thermodynamic, kinetic and electronic characteristics, some Mg-based alloy compositions can exhibit exceptional ‘glass-forming ability’ when cast from a melt. To date, majority of Mg-based glass-forming compositions are based on Mg–TM–RE or Mg–TM–Ca ternary systems (where TM = transition metals Cu, Ni, Zn, Ag and RE = rare-earth metals Y, Gd, La, Nd, Ce, etc.) [4-8] with critical casting sizes of up to 27 mm [8]. However, Mg-based metallic glasses have traditionally been rich in these solute elements making them relatively heavy (dense) compared to crystalline Mg alloys.

Another key issue plaguing the use of Mg-based glasses - at least in small-scale structural applications is their inherent low fracture toughness or brittle nature. This shortfall in mechanical performance is inevitably due to a low activation energy of shear banding - which is directly associated with the chemistry of these glasses, and the rapid structural relaxation effects they exhibit [8]. Due to their low glass transition temperatures (Tg) severe embrittlement can occur even at room temperature over relatively short timescales, strongly compromising their potential usefulness and commercial viability [8]. However, there are some examples that do point to a more positive design direction for these high-potential materials.

Considerable ductility of amorphous ribbons has been reported by Gu et al. in Mg–Zn–Ca alloys with Mg concentrations from 68 to 85 at% and by Guo et al. in in the Mg–Cu–Ca, Mg– Cu–Y and Mg–Ni–Y systems for alloys with a Mg content >85 at.% [8]. Modest ‘bulk’ glass ductility has also been observed in Mg-rich Mg–Ni–Gd-based [6] and Mg–Ni–Ca [9] alloy systems, pointing to higher Mg-contents (which simultaneously lowers their density) and lessening the degree of electronic charge transfer between elements (i.e. the degree of covalency in bonds) as a first step to improving the bulk ductility of these materials [8].

The ductility of Mg-based metallic glasses can also be significantly improved by the incorporation of ductile crystalline phases [10]. However, a significant volume fraction of crystallites in such a composite microstructure often results in the deterioration of strength and corrosion resistance, further, composite microstructures are often difficult to produce, requiring specific cooling rates or specialised processing techniques [10].

Here, we present relative comparisons to crystalline Mg-alloys, recent results, developments and design strategies in overcoming the former shortfalls of Mg-based bulk metallic glasses and future possibilities for a range of new, light-weight, ‘ductile’ Mg-rich bulk metallic glasses.

References

[1] M.F. Ashby, A.L. Greer Metallic glasses as structural materials Scripta Materialia 54 (2006) 321-326

[2] M.D. Demetriou et al., A damage-tolerant glass Nature Materials 10 (2011) 123-128

[3] J. Schroers Processing of Bulk Metallic Glass Advanced Materials 21 (2010) 1-32

[4] A. Calka, M. Madhava, D.E. Polk, B.C. Giessen, H. Matyja, J. Vander Sande, A Transition-Metal-Free Amorphous Alloy Mg70Zn30, Scripta Metallurgica, 2 (1977) 65-70

[5] K.J. Laws, K.F. Shamlaye, J.D Cao, J.P. Scicluna, M. Ferry Locating new Mg-based BMGs free of rare-earth elements Journal of Alloys Compounds 542 (2012) 105-110

[6] E.S. Park, H.J. Chang, D.H. Kim Mg-rich Mg–Ni–Gd ternary bulk metallic glasses with high compressive specific strength and ductility Journal of Materials Research 22 (2007) 334-338

[7] Q. Zheng, J. Xu, E. Ma High glass-forming ability correlated with fragility of Mg–Cu(Ag) –Gd alloy Journal of Applied Physics 102 (2007) 113519

[8] K.J. Laws, D. Granata, J.F. Löffler, Alloy design strategies for sustained ductility in Mg-based amorphous alloys – Tackling structural relaxation Acta Materialia (2015) DOI:10.1016/j.actamat.2015.08.077

[9] K.J. Laws, J.D. Cao, C. Reddy, K.F. Shamlaye, B. Gun, M. Ferry Ultra magnesium-rich, low-density Mg–Ni–Ca bulk metallic glasses Scripta Materialia 88 (2014) 37-40

[10] M. Ferry, K.J. Laws, C. White, D. Miskovic, K.F. Shamlaye, W. Xu, O. Biletska; Recent developments in ductile BMG composites MRS Communications 3 (2013) 1-12.

Magnesium

Technology 2016

Solidification and Casting

IN SITU SYNCHROTRON RADIATION DIFFRACTION OF THE SOLIDIFICATION OF Mg-Dy(-Zr) ALLOYS

Domonkos Tolnai*¹, Peter Staron¹, Andreas Staeck¹, Helmut Eckerlebe¹, Norbert Schell¹, Martin Müller¹, Joachim Gröbner², Norbert Hort¹

¹Institute of Materials Research, Helmholtz-Zentrum Geesthacht, Max-Planck Str. 1, Geesthacht, D21502, Germany

²Institute of Metallurgy, Clausthal University of Technology, Robert-Koch-Str. 42, D-38678 Clausthal-Zellerfeld, Germany

*Corresponding author. Tel: +49 4152 871974 e-mail address: domonkos.tolnai@hzg.de

Keywords: Mg alloys, solidification, in situ, synchrotron diffraction

Abstract

Mg-Dy alloys are attractive for biomaterial applications. Their mechanical property profile is close to that of cortical bone, they are non-toxic, osseoconductive and degradable. Their macroscopic characteristics depend on their microstructure, which can be tailored through the alloy composition and the solidification parameters. In situ synchrotron radiation diffraction is a tool to unequivocally follow the phase formation and grain growth during cooling, thus determining the solidification sequence. In the present study Mg alloys containing Dy and Zr were investigated to characterize the solidification phenomenon during cooling from 660°C to 200°C. Samples, contained in steel crucibles, were melted in a modified induction furnace for in situ synchrotron radiation measurements at the HZG beamline P07B (HEMS) at PETRA III, DESY, with the temperature controlled by type K thermocouples during the measurements. The results give an experimental validation of the thermodynamic calculations and input for refining the existing thermodynamic models. This contributes to a better understanding of the microstructure evolution thus to control desirable macroscopic characteristics.

Introduction

Mg alloys with Rare Earth (RE) additions are attractive for biomaterial applications as degradable bone implants [1]. Their mechanical property profile is close to that of cortical bone, they are non-toxic, osseoconductive and they degrade with time, sparing the implant removal surgery [2]. Besides being biocompatible Dy has a high solubility (25.4 wt.%) in Mg, which allows the wide range tailoring of the macroscopic mechanical properties. The UTS of Mg5Dy is 180 MPa while of Mg25Dy is 402 MPa [3]. Mg has three intermetallic compounds with Dy, Mg24Dy5, Mg2Dy and MgDy as shown in the Mg-Dy binary phase diagram in Figure 1.

In the case of multiphase materials the mechanical property profile depends strongly on the chemical composition, volume fraction and spatial distribution of the intermetallic phases [4]. These alloys are produced mainly in the form of castings and, as such, these microstructural parameters are determined during the solidification [5,6] and the following thermo-mechanical processing [7]. Therefore, the understanding of the sequence of formation and evolution of the meta-stable and stable phases during solidification is a prerequisite to achieve control of the microstructure of these alloys.

Performing in situ diffraction experiments while cooling the molten sample to the fully solidified state, allows identifying the microstructural phases, to determine their solidification sequence [8,9,10] and to use the results for experimental validation of the existing thermodynamic databases.

Figure 1. Mg-Dy binary phase diagram [11].

The aim of this investigation is to perform in situ synchrotron diffraction during solidification of a Mg20Dy alloy unmodified and modified with Zr, and to compare the experimental results with the existing thermodynamic data on this system.

Experimental methods

Alloy production

The alloys Mg20Dy(-0.4Zr) were chosen because of the particular interest in biomaterial applications. The alloy Mg20Dy was prepared by permanent mould indirect chill casting as described in [12]. The materials were melted in an electric resistance furnace under protective atmosphere of Ar with 2% SF6. Dy was added as a pure element. To modify the alloy with Zr, it was remelted and casted into steel moulds.

Microstructural characterization

The microstructures of the alloys were investigated with a Carl Zeiss Gemini Ultra 55 Scanning Electron Microscope (SEM) operated at 15kV and equipped with an EDAX energy dispersive X-ray spectrometer (EDXS).

In situ synchrotron diffraction

The samples for the synchrotron diffraction measurements were cut into small cubes and encapsulated in steel crucibles. The experiments were carried out at the HZG beamline, HEMS P07B beamline at the PETRA III at the Deutsches Elektronen-Synchrotron (DESY). The measurements were performed in the chamber of a furnace, heated by an induction coil. There are two windows on the sides covered by Kapton foils, to prevent interference with the X-ray beam, while the chamber itself is floated with Ar. The measurement setup is shon in Figure 2. During the tests the samples were held in a sealed stainless steel crucible in order to hold the molten metal and to isolate it from the surrounding atmosphere. The temperature was regulated by a type K thermocouple welded on the steel crucible containing the sample. To melt the samples the system was heated up to 660 °C, held for 5 min and then cooled to 200 °C at a cooling rate of 5K/min, 10 K/min and uncontrolled cooling with