Asian Program

Japanese

Data

Former Fellows

Dissertation Abstracts

Korea

At Icho-kaikan(Place of ceremony)

  Ultrafine grained (UFG) Al alloys, which have submicron grain structures, are expected to show outstanding high strength at ambient temperature and excellent superplastic deformation at elevated temperatures and high strain rate. In order to get the UFG microstructure, various kind of severe plastic deformation (SPD) processes have been developed. Among these processes, accumulative roll bonding (ARB) process is a promising process to make bulky Al sheets with ultrafine grained structure continuously. Although many researches on the microstructural evolution in commercial purity Al alloys (especially in AA1100 Al sheets) during the ARB process have been performed, the deformation behaviors, texture properties, annealing behaviors and effect of alloying elements of the UFG materials manufactured by the ARB process have not been investigated in detail. The purpose of the present study is to clarify the grain refinement mechanism during the ARB process and to investigate the correlation between the ultra-fine grained structure and the mechanical properties.
  Most UFG aluminum alloys previously manufactured by SPD processes had showed high strength and low tensile ductility due to the lack of strain hardening at ambient temperature. Exceptionally, the author found in the present study that the UFG AA8011 alloy (Al-0.72wt%Fe-0.63wt%Si) manufactured by the ARB had fairly large tensile elongation, keeping the high strength. In order to clarify the reason for the increase of elongation in the UFG AA8011 alloy, detailed microstructural and crystallographic analysis was performed by TEM/Kikuchi-line and SEM/EBSP method. The unique tensile properties of the UFG AA8011 alloy could be explained by enhanced dynamic recovery at ambient temperature, owing to the large number of high angle boundaries and the Al matrix with high purity. The dynamic recovery of the UFG AA8011 alloy was evaluated by the strain rate sensitivity (m), which gave a great effect on post-uniform elongation. On the basis of the detailed study on the microstructure and tensile deformation behaviors in the UFG AA8011 alloy, the effect of alloying elements on the formation of UFG structure and tensile properties was discussed to establish the optimized alloy design in commercial purity Al alloys.