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URN etd-0802106-162003 Statistics This thesis had been viewed 2597 times. Download 406 times. Author Yu-Shuo Chan Author's Email Address No Public. Department Materials Engineering Year 2005 Semester 2 Degree Master Type of Document Master's Thesis Language English Page Count 143 Title A Study on the Strain Softening and Anneal Hardening in Pseudo-single- and Dual-phase Zn-Al Alloys Keyword dynamic recrystallization (DRX) Zn-Al alloy work softening anneal hardening anneal hardening work softening Zn-Al alloy dynamic recrystallization (DRX) Abstract In this study thermomechanical processings were applied to three Zn-Al alloys, namely the micro-duplex Zn-22 wt.% Al alloy, pseudo-single α phase Zn-95 wt.% Al and pseudo-single β phase Zn-1wt.% Al for the strain softening and anneal hardening studies. The microstructure, hardness and compression S-S curves of these Zn-Al alloys were studied by using differential scanning calorimetry (DSC), scanning electron microscopy (SEM), microhardness measurements and compression tester. The results showed the occurrence of a strain softening phenomenon in Zn-Al alloys containing a substantial amount of β phase in the temperature range from -10℃ to 250℃ and an anneal hardening behavior in the strain softened Zn-Al alloys upon high temperature annealing. The mechanism of the strain softening behavior was found to be a DRX-induced softening during hot working, which can be facilitated by the formation of ultra-fine β grains with high-angle-boundaries; the mechanism of the anneal hardening behavior, on the other hand, was found to be the annihilation of the ultra-fine β grains by a high temperature grain coarsening treatment to retard the occurrence of the DRX-induced softening and to restore the “normal strength” of the alloy.
A composite stress-strain curve model was proposed in this study to resolve the strain softening and anneal hardening behaviors in the dual-phase Zn-22 wt.％ Al alloy. By using this model detailed informations regarding to the deformation, the DRX (i.e. the strain softening) and the grain coarsening (i.e. the anneal hardening) behaviors in the β phase can be disclosed.
Advisor Committee Chih-Fu Yang - advisor
Jien-Wei Yeh - co-chair
Lui-Ho Chiu - co-chair
Shu-Chun Lin - co-chair
Files Date of Defense 2006-06-30 Date of Submission 2006-08-02