Title page for etd-0719112-164036


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URN etd-0719112-164036
Author Hung-Ya Liao
Author's Email Address m993100009@student.nsysu.edu.tw
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Department Materials and Optoelectronic Science
Year 2011
Semester 2
Degree Master
Type of Document
Language zh-TW.Big5 Chinese
Title Effect of Equal Channel Angular Extrusion on the Microstructure Evolution and Mechanical Properties of Al-5wt%Zn Alloy
Date of Defense 2012-06-15
Page Count 135
Keyword
  • strain rate sensitivity
  • grain boundary sliding
  • activation volume
  • high angle grain boundaries
  • post-uniform elongation
  • equal channel angular extrusion
  • Al-Zn alloy
  • Abstract In this work, ultrafine-grained (UFG) Al-5wt%Zn alloy was produced by equal channel angular extrusion (ECAE). The microstructure evolution during ECAE and the mechanical properties of the UFG Al-Zn alloy were investigated. In order to identify the effect of Zn in the Al-Zn alloy, pure aluminum (4N, 99.99%) was also studied for comparison. The grains of the Al-Zn alloy could be refined effectively by increasing the ECAE passes. However, as the ECAE passes increased, the microhardness increased initially but maintained constant after 4 ECAE passes. The dislocation density within grain interior was decreased gradually with increasing ECAE passes. After being processed to twelve ECAE passes, the UFG Al-Zn alloy exhibited 53.7% of the grain boundaries being high angle grain boundaries (HAGBs).
    The UFG Al-5wt%Zn alloy exhibits superior tensile strength and elongation as compared with pure aluminum fabricated by the same ECAE process. Experimental results indicated that adding Zn in aluminum alloy could provide solid-solution strengthening and considerable enhancement in tensile ductility which might be related to an improved post-uniform elongation (PUE). The strain rate sensitivity (SRS) of the UFG Al-Zn alloy also increased with increasing the ECAE passes, which might be related to the fine grain size and the contribution of grain boundary sliding. The activation volume of the UFG Al-Zn alloy was in the range of 32b3~76b3, and the pure aluminum was in the range of 57b3~122b3. Because of the small value of the activation volume, it is suggested that the controlling mechanism for dislocation glide in the UFG Al-Zn alloy might be related to the generation and absorption of dislocations in grain boundary, as well as the interaction between dislocations and solute Zn atoms in the grain boundary.
    Advisory Committee
  • Chih-Pu Chang - chair
  • Chung-Yi Yu - co-chair
  • Po-We Kao - advisor
  • Files
  • etd-0719112-164036.pdf
  • Indicate in-campus at 5 year and off-campus access at 99 year.
    Date of Submission 2012-07-19

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