Platform Science and Technology for Advanced Magnesium Alloys -Extra Light Metals in the 21st Century-

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In the current four-year term project, new platform science and technology is proposed as a core concept of research and development of advanced magnesium alloys together with understanding of their intrinsic characteristics. The research fields related to advanced super-light magnesium alloys for 21st Century have been focused to the selected three categories ; ( 1)Search for new premium alloys and a structural design from the view points of microstructure control, (2)Establishment of environmental-friendly surface modification and recycling for the ecomaterials desing and green processing, and (3)High performance design and processing in functionality. Each research group is introduced together with its strategic directions toward future R & D for advanced magnesium alloys and has its own joint research network to drive new research directions.Typical results are summarized as follows ; a nanocrystalline Mg-1mol%Zn-2mol%Y bulk alloy sample prepared by warm extrusion of rapidly solidi … More fied powders is composed of grains of about 50-200 nm in diameter, which are divided into two types; hcp-Mg solid solution grain and fine-lamellar grains consisting of a novel long-period ordered structure with hexagonal lattice of 6H-type (ABCBCB)., resulting in high 0.2% proof strength of about 610 MPa and sufficient elongation of about 5% at room temperature. Dislocation cross slip from basal plane to non-basal planes, dynamic recovery within twins and in untwined matrix, and grain boundary sliding are found to occur in whole grains of the magnesium alloy specimens with fine-grains of lower than 10μm even at room temperature. AZ61 alloy specimen indicates high strength of 350MPa and high ductility of 33% by the refinement of grains and precipitates caused by dynamic recrystallization and dynamic precipitation during severe warm working. To be free from the classical theory, materials design on the basis of the first principle molecular dynamics calculation is proposed for new high creep resistant magnesium alloys. A protective high purity coating applying magnesium vapor deposition technique, polymer plating of triazine dithiols easily peeled at the cryogenic temperature or decomposed by brittle fracture, and their solid state recycling technology are developed as environmentally benign surface modification without chromium. The co-electrodeposition of rare earth metals (RE) with Mg in the molten salt system including RE chlorides is found to be available for the production of Mg-RE alloys. Also, semi-solid continuous casting process is established for the fabrication of fine-and globular-grained billet and adequate magnesium alloys is developed for high speed semi-solid processing at lower temperatures as a near net complex shape forming process. As a new route to fabricate the functional magnesium alloys, bulk mechanical alloying process as a solid state synthesis was proposed to successfully synthesize the magnesium base hydrogen absorbing alloys and thermoelectric semiconductor in the solid state with fine structure and accurate chemical composition. This bulk mechanical alloying also provides us non-equilibration to make solid state synthesis. Furthermore, ternary or quaternary magnesium base alloy bulk can be directly fabricated to have the same chemical composition as predicted in design at extremely lower temperature than the melting temperatures of constitutive elements. On this fundamental knowledge, the solid-state recycling is proposed to fabricate the reinforced magnesium alloy composite parts and performs with in-situ precipitated Mg_2Si and MgO in fine and uniform.On the basis of the obtained results, platform science and technology for environmentally benign and high performance magnesium alloys is constructed as an industrial base material for the next generation. Less