| Summary: | 碩士 === 國立東華大學 === 材料科學與工程學系 === 100 === In order to develop a high strength age-hardenable magnesium alloy, and expand the application of wrought magnesium alloys, the ZK60 alloys with high strength were investigated in this study. Two-stage aging(combined with 70℃ and 160℃) or T8 heat treatment were used to increase the heterogeneous nucleation sites and accelerate the precipitate rate.
In two-stage aging condition, G. P. zones were formed during pre-age process; however, they were dissolved again under 160℃ aging treatment, which could not help to enhancing the aging-hardening ability efficiently. Within T8 heat treatment, the fiber structures or twins were formed by an severer plastic deformation, and these defects were used to be the heterogeneous nucleation sites. These defects were so stable even at elevated temperatures, but they could accelerate the nucleation and growth rate of those precipitates, and this would decrease the aging-hardening ability.
The morphology and microstructure of those precipitates appeared during artificial aging process were be investigated by TEM. The β1’ phase which appeared during pre-aging condition was confirmed to be long rod-liked Mg4Zn7, and the β2’ phase which appeared during over-aged condition was short long rod-liked MgZn2.
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