Mg Science & Technology Workshop - Fundamental Research Issues
Held May 19-20, 2011
Sean R. Agnew, Organizer
Heinz and Doris Wilsdorf Research Chair and
Associate Professor of Materials Science and Engineering
University of Virginia
395 McCormick Rd
Charlottesville, VA 22904-4745
in consultation with the Workshop Steering Committee
Eric Nyberg, Pacific Northwest National Lab (Co-Organizer)
Tresa Pollock, UC Santa Barbara
Robert Wagoner, the Ohio State University
Bob Powell, General Motors
Ray Decker, Thixomat, Nanomag LLC
Donald Shih, The Boeing Company
Workshop Overview: A 2-day workshop held on May 19 and 20 in Arlington, Virginia brought together a diverse group of 52 scientists and engineers from academia, government laboratories, industry, and funding agencies to i) identify the outstanding fundamental science issues which inhibit broader application of Magnesium (Mg) alloys in structural (including biomedical) applications and ii) to recommend research directions to address the outstanding issues. Notably, fellowships to attend the workshop were issued to four graduate students, who are interested in academic or research-intensive careers, providing them with a unique perspective of a part of the research process that students rarely see. Two other local graduate students were also able to attend and participate in all aspects of the workshop. This final report summarizes the deliberations and recommendations of the participants.
Workshop Commission: The current renaissance in Mg application and R&D was initiated by interest from the automotive industry, with the primary driver being vehicle mass reduction for improved vehicle efficiency and performance. Interest has expanded into the consumer goods sector with a large number of manufacturers selecting to die cast or semi-solid molding of Mg alloys for the cases of handheld tools and portable electronic goods. Now, the aerospace, defense, and biomedical sectors are all developing interest in strategies to exploit the lightest structural metal in the periodic table of elements. However, there are a variety of application areas which require either better alloy properties or better understanding of how to process and/or design with Mg alloys before broader application will be possible.
Workshop Agenda: 12 invited speakers presented 11 lectures designed to set the tone for the smaller group discussions (see Appendix A for a detailed schedule). The invited speakers represented a broad cross-section of industry, academia and national laboratories from across the globe. They described recent advances and highlighted remaining gaps in our understanding of Mg alloys as well as their personal perspectives regarding opportunities for scientific impact, given new advanced experimental techniques and computational methods. The subsequent break-out discussion sessions addressed 13 topical areas of research (see Appendix B).
The results of those discussions are synthesized into recommendations in eight sections of this final report: Casting and Solidification, Alloy Development, Coatings and Corrosion, Mechanical Performance, Deformation Processing, Joining and Fastening, Flammability and Aerospace Concerns, and Integrated Computational Materials Engineering (ICME). This document should help research sponsors and researchers alike to focus future efforts on those areas that are considered most important and/or appear to have the greatest promise. A short summary of the recommendations follows on the next page.
Summary of Recommendations
Mg alloys play an increasingly important role in structural applications, which demand the light weighting potential of the lowest density structural metal. This is most obvious in the recent, marked increase in the use of Mg alloy die castings for automotive interior parts and consumer products. More aggressive application of Mg alloys in situations demanding greater corrosion resistance, strength, workability, and tolerance for dynamic loading will require active research and development to overcome outstanding scientific and technical barriers.
The following list highlights the areas in greatest need of fundamental research:
The poor corrosion resistance of Mg alloys demands a focus on slowing the kinetics of dissolution. Improved fundamental understanding of the mechanisms of corrosion will enable the development of game-changing alloy compositions/surface modifications designed to promote better surface film properties and/or improved barriers (coatings) at the interface with the environment. These approaches should be pursued in parallel, in order to overcome what many view as the critical obstacle to broader application of Mg.
There is a need to enhance the mechanical behavior (formability, strength, fatigue, fracture, creep) relevant to deformation processing and application. The unifying theme is a need to improve the understanding of the fundamentals of anisotropic plasticity of hexagonal close packed crystals, including the roles of deformation twinning, shear localization, and the effects of alloying (solute and precipitates) on various deformation mechanisms. Without this understanding, alloy and microstructure design efforts will proceed in an empirical, data-driven manner at a pace too slow for incorporation into modern engineering applications.
The knowledge base of Mg alloy thermodynamics is developing quickly, yet that pertaining to kinetics lags. There is a need for more diffusion data and understanding of non-equilibrium phase transformations relevant to solidification, precipitation, and creep. Models of structure evolution during thermal processing and under service conditions are poorly developed, due to inadequate knowledge of system kinetics.
Finally, because there are more gaps in the fundamental scientific understanding of Mg based alloys, as compared to more heavily studied ferrous, aluminum, and nickel based alloy systems, they are considered ripe to benefit from increased computational modeling, including that relevant to corrosion, deformation mechanisms, alloy and microstructure design, processing (casting and forming), and performance (failure prediction & mitigation). Integrated approaches which span this entire spectrum and permit new design paradigms are viewed as optimal.