Title page for etd-0610113-100208


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URN etd-0610113-100208
Author Zheng-han Li
Author's Email Address guahanli@gmail.com
Statistics This thesis had been viewed 5330 times. Download 139 times.
Department Materials and Optoelectronic Science
Year 2012
Semester 2
Degree Master
Type of Document
Language zh-TW.Big5 Chinese
Title Tensile Deformation of Ultrafine Grained Al-Zn Alloys
Date of Defense 2013-07-05
Page Count 81
Keyword
  • SRS
  • activation volume
  • GBS
  • PUE
  • Al-Zn alloy
  • ECAE
  • Abstract In this work, ultrafine-grained (UFG) Al-5wt%Zn alloy was produced by equal channel angular extrusion (ECAE) with 120 degree die. The tensile deformation behavior of this UFG Al-5wt%Zn alloy was investigated at temperatures ranging from 77 K to 473 K with various strain rates. In order to identify the effect of Zn in the Al-Zn alloy, pure aluminum (4N, 99.99%) was also studied for comparison.
    The tensile elongation of the UFG Al-5wt%Zn alloy increases with increasing temperature. After the same ECAE processing, the UFG Al-5wt%Zn alloy possesses higher tensile strength and elongation than pure aluminum. The improved tensile elongation of the UFG Al-5wt%Zn alloy is mainly due to the contribution of post-uniform elongation (PUE), which can be related to increased strain rate sensitivity (SRS). Observations of the surface of tensile tested specimen revealed the evidence of grain boundary sliding (GBS) in the UFG Al-5wt% Zn alloy. It is proposed that the addition of Zn may enhance the grain boundary diffusion in the UFG Al-Zn alloy and facilitate the process of GBS. It is believed that the enhanced GBS is responsible for the increasing of PUE with increasing temperature. At low strain rates, 1- 4 x 10-5s-1, the UFG Al-5wt% Zn alloy exhibits yield phenomenon and dynamic strain aging at 373 K - 423 K, which result in increased work-hardening rate and tensile elongation.
    The activation volume (v*) of the UFG Al-Zn alloy is in the range of 21b3~41b3 for the temperature range studied. Based on the small value of the activation volume, it is suggested that the controlling mechanism for tensile deformation in the UFG Al-Zn alloy might be related to the generation and absorption of dislocations in grain boundary, which is affected by the interaction between dislocations and Zn atoms in the grain boundary.
    Advisory Committee
  • Chih-Pu Chang - chair
  • Chung-Yi Yu - co-chair
  • Po-We Kao - advisor
  • Files
  • etd-0610113-100208.pdf
  • Indicate in-campus at 5 year and off-campus access at 5 year.
    Date of Submission 2013-07-10

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