Title page for etd-0801111-154329


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URN etd-0801111-154329
Author Yi-Chia Huang
Author's Email Address iloveuehara@yahoo.com.tw
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Department Materials and Optoelectronic Science
Year 2010
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-15wt%Zn Alloy
Date of Defense 2011-06-30
Page Count 114
Keyword
  • microstructure
  • strain rate sensitivity
  • activation volume
  • post-uniform elongation
  • equal channel angular extrusion
  • Al-Zn alloy
  • Abstract    The deformation mechanism of an ultrafine grained (UFG) Al-Zn alloy has been studied. In this work, Al-15wt%Zn alloy was processed by equal channel angular extrusion (ECAE) route A at 100oC to achieve UFG structure. The deformation mechanism was studied by performing tensile test with various strain rates.
       Scanning electron microscopy and transmission electron microscopy were used to investigate the microstructure evolution in Al-15wt%Zn alloy with increasing ECAE passes. The observation indicated that the super saturated Al-Zn alloy would decompose and precipitate Zn particles during ECAE process. Increasing ECAE passes, the aluminum grain size was reduced, but the size of Zn particles was increased. However, the net effect of increasing ECAE passes is softening of this Al-Zn alloy.
        The tensile properties of the UFG Al-Zn alloy can be summarized as follows.
    (1)The UFG Al-Zn alloy possesses higher tensile strength and elongation as compared to commercial purity Al (AA1050).
    (2)The strain rate sensitivity of the UFG Al-Zn alloy increases significantly with increasing number of ECAE pass, which might be related to the refined aluminum grain size. After processed by 4-16 ECAE passes, the activation volume of the UFG Al-Zn alloy falls in the range of 25 b3~40 b3, which remains nearly constant value with increasing tensile strain. It is suggested that the controlling mechanism
    responsible for the tensile deformation of the UFG Al-Zn alloy might be related to a grain boundary mediated mechanism.
    (3)With increasing ECAE passes, the total tensile elongation of the UFG Al-Zn alloy increases but the uniform elongation show little change. This indicates that the increase in total elongation is mainly due to the contribution from an enhanced post-uniform elongation (PUE). It is suggested that the enhanced PUE might be related to the increase in strain rate sensitivity, which is resulted from the refinement of grain size. More detailed studies are needed to understand the deformation mechanism.
    Advisory Committee
  • Chih-Pu Chang - chair
  • Liu-Wen Chang - co-chair
  • Po-We Kao - advisor
  • Files
  • etd-0801111-154329.pdf
  • Indicate in-campus at 3 year and off-campus access at 5 year.
    Date of Submission 2011-08-01

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