Invention of high performance magnesium alloys with trade-off balancing by multi-scale controlling

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This research purpose is the invention of the high performance magnesium alloys, which are trade-off balanced by multi-scale controlling from electron or atomic level to macroscopic level. The results are summarizes to below.(1)In "the analysis for deformation behavior and an alloy design by the first principle molecular dynamics calculation", the big difference in the critical resolved shear stress between basal and prismatic slip planes, which leads to the brittle-nature of magnesium, was discussed from the results by theoretical calculation on the generalized stacking fault energy in ideal slip deformation of each single crystal. As the result it was found that an addition of Li, Al or Zn could make the difference small. Moreover, the anisotropy of the bonding strength was discussed from the electron density distribution.(2)In "the construction of the materials process for the alloy having an excellent in mechanical property and formability", an improvement in the impact properties … More was attained by the uniform distribution in fine Zr-precipitates and the grain refinement on the Mg-Zn system alloy processed by equal-channel-angular-extrusion (ECAE). Moreover, the strain-rate reverse dependency of the elongation was found in the ECAE processed Mg-AI system alloy (AZ31) by the achievement of grain refinement and texture control, and improvement in no less than 50% elongation was attained under an impact strain-rate of 1.8 x 10^3 s^<-1> at room temperature. Moreover, it was shown clearly that low temperature or high-strain-rate superplasticity could be discovered in various alloys.(3)In "the establishment of the diffusion bonding and the friction stir welding technology", the equation describes the diffusion bonding condition was drawn from the cavity-disappearance model in the compressive superplastic deformation, and it was shown that the bonding strength of AZ31 alloy sufficient in one third of the bonding time of aluminum under an optimal condition could be obtained. Moreover, although, as for pure magnesium, sufficient bonding strength was not obtained in friction stir welding, with the alloy, 90% or more of the bonding strength of mother material was obtained.(4)In "the establishment of the press fabrication technology from rolling sheets", it was found that the forming limit depended on the fracture limit of the tensile bending on the punch shoulder, and it improved by heating at 473 K or less. Moreover, it was shown that the local deformability, which was hard to evaluate by the tensile test, was important to obtain the good press fabrication, and the new method to evaluate the formability by a notched-specimen bending test was proposed. Less