Title page for etd-0831111-151623


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URN etd-0831111-151623
Author Wen-Tu Lee
Author's Email Address No Public.
Statistics This thesis had been viewed 5344 times. Download 117 times.
Department Materials and Optoelectronic Science
Year 2010
Semester 2
Degree Ph.D.
Type of Document
Language zh-TW.Big5 Chinese
Title The Production and Deformation Behaviour of Ultrafine-Grained AZ31 Mg Alloy
Date of Defense 2011-07-26
Page Count 230
Keyword
  • Equal-channel angular extrusion(ECAE)
  • Grain refinement
  • Ultra-Fined Grain
  • Mg alloy
  • Shear Band
  • Abstract Ultrafine-grained(UFG) AZ31 Mg alloy was obtained by equal-channel angular extrusion(ECAE) and subsequent annealing at elevated temperatures. The basal texture component for ECAEed material is located on the Z plane of the ECAEed billets. Tensile tests were performed at temperatures between room temperature and 125℃, and strain rates used ranging from 3*10-5 to 6*10-2 s-1. The experimental results showed that a high tensile yield stress of 394 MPa was obtained at room temperature under a strain rate of 3*10-3 s-1. Strengths of UFG AZ31 specimens were greatly improved due to grain refinement. It was found that strain rate sensitivity of UFG AZ31 alloy increased significantly from 0.024 to 0.321 with increasing temperature. The constant k of Hall-Petch equation, σ=σ0 +kd-1/2, decreased with increasing temperature, and decreasing strain rate. Negative k values were ontained at 75℃ and 100℃ under a strain rate 3*10-5 s-1.
    When compressed along X, Y and X45Z billet orientations, strain localization within shear bands was found in UFG AZ31 specimens. Shear bands are formed inclined near 45 to the compression axis. The smaller the grain size, the thinner the shear band. Different Hall-Petch constant k were found in specimens deformed along different orientations, which is caused by different deformation mechanisms. The formation of  tension twins is the primary deformation mechanism for compressed X and Y samples, and basal slip is responsible for the deformation of X45Z sample.  tension twins were found in 0.46 μm grain size specimens.
    Advisory Committee
  • Po-We Kao - chair
  • Jian-Yin Wang - co-chair
  • Der-Shin Gan - co-chair
  • Li-Hui Chang - co-chair
  • Chih-Pu Chang - advisor
  • Files
  • etd-0831111-151623.pdf
  • Indicate in-campus at 5 year and off-campus access at 5 year.
    Date of Submission 2011-08-31

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