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Deformable and corrosion resistant novel mg alloys via rapid solidification

Research on cold-deformable & corrosion resistant mg-li based alloys & processing technologies from rapid solidification to near-net- shape forming, for automotive/electronic industries committed to the tokyo protocol and sustainable development in portable electronics.

Magnesium (Mg), being the lightest structure metal, has tremendous potential for replacing steel, aluminium (Al) and plastics in automobiles and electronic appliances. Its applications have however been seriously hindered by its notoriously poor deformability at temperatures below 225 degrees Celsius when converting a starting stock into an end product and also by its high susceptibility to atmospheric and galvanic corrosion in practical applications. The techniques recently developed, such as applying equal-channel angular pressing to refine grain structure and restricting impurities, can remarkably improve the performance of Mg, but the technological barriers to its wider applications have essentially not yet been cleared. This is because these techniques do not change the intrinsic properties of Mg: hexagonal close-packed (HCP) lattice structure with a highly limited number of operative slip systems and very low electrochemical and chemical potential. Another effective technique, alloying to create a new set of intrinsic properties, is only restrictedly applicable due to severe segregation occurring during the conventional casting processes. To solve this problem, an international consortium has been established with the objectives being to push the alloying limitations as imposed by the conventional Mg processing methods and then to circumvent the barriers to its wider applications. These objectives will be reached through fundamental research on novel Mg alloys and related processing technologies from rapid solidification with a cooling rate of 106 degrees Celsius/second to near-net-shape forming. It is expected that by virtue of extra-fine grain structures in the range of 500-1,000 nm, largely retained throughout material processing, the threshold temperature for deformation will be significantly decreased to as low as 100 degrees Celsius. More importantly, through the addition of a substantial amount of lithium (Li), not achievable with the conventional ingot casting, a highly deformable body-centred cubic (BCC) lattice structure will be formed, thus further enhancing the warm and cold deformability of Mg. An additional advantage of this alloying is a further reduction of the gravity of Mg alloys to a level merely 50% of Al alloys, thus further enhancing its specific elastic modulus and strength. Furthermore, extended solid solutions of various elements in a very fine, homogeneous alpha-Mg matrix will shift the electrolytic potential of Mg to much more prestigious values, thus significantly improving atmospheric and galvanic corrosion resistance and reaching a corrosion resistance level comparable with Al alloys. To reach the objectives, a complete set of research activities has been planned and will take place in the following phases. 1) Design and preparation of new Mg alloys - to study a series of novel Mg-Li based alloys, on the basis of a fundamental understanding of the thermodynamic and kinetic interactions between Mg, Li and other minor alloying elements during rapid solidification and subsequent processing, in order to attain maximum solid solutions and minimum segregation and to preserve structural attributes throughout processing. 2) Optimisation of rapid solidification processes - to use melt spinning as a basic method for determining the influence of process parameters (tangential velocity of rotating wheel, injection pressure, injection angle, melt superheat, nozzle/wheel distance, nozzle dimensions and atmosphere) on melt-spun ribbon quality (thickness, width, dimensional stability, oxidation level, etc.) on both laboratory and pilot scales. 3) Characterisation of rapidly solidified Mg alloys - to determine the initial micro-structural characteristics on the cross-section of the ribbons having undergone varying solidification and cooling rates, including micro-segregation, metastable, nano-sized second-phase particles, supersaturation, grain structure, texture, oxidation and hydrogen pick-up, by means of SEM (Scanning Electron Microscope), EPMA, TEM (Transmission Electron Microscopy), XRD (X-Ray Diffraction), AES (Auger Electron Spectrometry) and ESCA. 4) Optimisation of consolidation processes - to study the gas evolution phenomena during degassing as a function of temperature, time and atmosphere by means of ICP (Intrinsically Conductive Polymer), AES and ESCA and to determine compactibility during uni-axial pressing and isostatic pressing and accompanying microstructural development by means of DSC (Differential Scanning Calorimetry), SEM, EPMA, TEM and XRD. 5) Optimisation of near-net-shape forming processes - to determine the deformability through compression tests (Gleeble 3,500) at varying temperatures and strain rates, and the extrudability, i.e. permissible extrusion speed as a function of extrusion temperature and extrudate geometry. 6) Electrochemical evaluation - to perform accelerated corrosion tests in aggressive environments and to determine the specific (electro)chemical parameters (potential, polarisation resistance, corrosion rate, galvanic current, etc.) aided by analyses by means of CSFM, AFM (Atomic Force Microscopy) and AES. 7) Mechanical evaluation - to determine tensile properties, compressive properties, bending properties, fatigue resistance and creep resistance. 8) Technical and economic assessment - to determine the ratio of material performance to material costs. Keywords: rapid solidification, extrusion, magnesium.
Acronym: 
DCRMG
Project ID: 
3 359
Start date: 
01-01-2006
Project Duration: 
48months
Project costs: 
4 950 000.00€
Technological Area: 
Metals and Alloys
Market Area: 
Motor Vehicles, Transportation Equipment and Parts

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