large in size, as this phase can be fragmented and embedded in the β matrix. The TEM observation also revealed that the as-cast and as-quenched LZ91 had dual phase microstructure with numerous ultra fine particles, identified as ZnO and MgO oxides. The orientation of the Wurtzite structure of ZnO, but not that of MgO, was found to be intimately related to that of the magnesium matrix. XRD analysis also revealed the presence of an extra bump adjacent to the main peak associated with α(0002) following the aging treatment at 50°C/100 h and 100°C/10 h, suggesting a product of spinodal decomposition. The precipitate was an unstable phase because it disappeared after subjected to long-time aging. The LZ91 alloy treated with peak aging conditions at 100°C underwent a short-range structural modification, which could be caused by spinodal decomposition.
The results of tension and formability tests indicated that the ductility of various Mg-Li-Zn alloys has been greatly enhanced with higher Li content. LZ61 alloy showed low ductility at ambient temperature; whereas, the high lithium content alloys, LZ91 and LZ101, possessed considerable ductility of more than 40％, which was close to that of AZ31 at elevated temperature. However, the inadequate %
elongation of LZ61 and AZ31 at room temperature demonstrated poor formability. On the other hand, the LZ alloys appeared to show insufficient strain hardening ability under the strain of 1×10-3S-1. As such, work-hardening of the alloy may be possible for enhancing the material’s formability by applying rapid strain rate during stretching deformation.
The n value decreased with the increasing lithium content in LZ alloy, and as the lithium content was higher than 9wt%, all of them were lower than 0.05. The forming limit curves of LZ91 and LZ 101 were located at higher position in the major strain versus minor strain plot than their AZ31’s counterparts at 100℃ and room temperature, indicating a better formability of the alloys at the strain of 1×10-3S-1.
FUTURE STUDIES
Magnesium-Lithium alloy is a promising metal for structural applications, such as portable electrical products, transportation vehicle and the like. As such, the formability of this new alloy in the plastic forming process during mass production is a critical issue needs to be addressed. Two major aspects associated formability are suggested for future research:
First, since friction coefficient plays a vital role in the stamping process, stamping using different lubricants and that with no lubrication are important issues need to be addressed in the forming of Mg-Li alloy sheets.
Secondly, LZ alloys have smaller n-values, but the formability could be improved by applying various strain rate, varied forming temperature and different stamping die design.
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LIST OF PUBLICATIONS
Journal Paper
1. C.H. Chiu, H.Y. Wu, J.Y. Wang and S. Lee, Microstructure and Mechanical Behavior of LZ91 Mg Alloy Processed by Rolling and Heat Treatments, Journal of Alloys and Compounds. (SCI), 2007. (In Press)
2. H.Y. Wu, C.H. Chiu, S.H Sheu, S. Lee and J.Y. Wang, Effect of die surface roughness on deformation characteristics and cavitation during blow forming in a superplastic 5083 alloy, Materials Transactions. (SCI), 2007. (In Press)
3. C.H. Chiu, J.Y. Wang, and H.Y. Wu, Microstructural Characterization and Mechanical Behavior of an Mg-9%Li-1%Zn Alloy, Materials Science Forum, Vol. 546-549, p.229-232, 2007. (SCI)
4. C.H. Chiu, J.Y. Wang, H.Y. Wu, Microstructural Characterization of an Mg-9%Li-1%Zn Alloy, Materials Transactions, Vol. 47, No. 4, p.966-970, 2006. (SCI)
5. H.Y. Wu, J.Y. Perng, S.H. Shis, C.H. Chiu, S. Lee, and J.Y.
Wang, "Cavitation Characteristics of a Superplastic 5083 Al Alloy during Gas Blow Forming, Journal of Materials Science, Vol. 41, No. 22, p.7446-7453, 2006. (SCI)
6. H.Y. Wu, C.H. Chiu, J.Y. Wang, S. Lee, "Effect of Lubrication on Deformation Characteristics of a Superplastic 5083 Al Alloy during Bi-axial Deformation, Materials Science and Engineering A, Vol. A427, p.268-273, 2006. (SCI)
7. 吳泓瑜、邱垂泓，鋁鋰合金材料性質與應用，工業材料雜誌，
Vol. 247, P.145-149, 2007.
8. 邱垂泓、吳泓瑜，鎂合金之超塑性成型，工業材料雜誌， Vol.
242, p.153-159, 2007.
9. 邱垂泓、王文寬，超輕鎂鋰合金性質及其應用，工業材料雜 誌，Vol. 233, p.163-170, 2006.
Conference Paper
1. C.H. Chiu, R& D Trend on Magnesium Alloys in Taiwan, 2nd
Yellow Sea Rim Magnesium Symposium, Gwangju, Korea, Mar 15, 2007. (Invited speaker)
2. H.Y. Wu , G.Z. Zhou, C.H. Chiu, J.Y. Wang and S. Lee, The Formability of an Mg-9%Li-1%Zn Alloy Thin Sheet, 2nd Asian Symposium on Magnesium Alloys. (Submit)
3. C.J. Liao, F.K. Chen, W.K. Wang, C.H. Chiu, Formability of LZ Magnesium Alloy Sheets, 2nd Asian Symposium on Magnesium Alloys. (Submit)
4. J.Y. Wang, Y.N. Lin, C.H. Chiu and S. Lee, Effect of Annealing on Solid State Recycled Magnesium Alloy AZ91D, 63rd Annual World Magnesium Conference, 2006.05.
5. 邱垂泓、王文寬、周耿中、許清賢、吳泓瑜，超輕鎂鋰合金
性質之研究，2005材料學會年會論文。
6. 周耿中、邱垂泓、吳泓瑜，LZ91鎂鋰合金之拉伸性質，2006 材料學會年會論文。
7. 邱垂泓 、王文寬、王建義，Mg-9%Li-1%Zn鎂合金微結構與
性質之研究，2006鎂合金協會年會論文，p214-225.
8. 廖志杰、陳復國、王文寬、邱垂泓，LZ系鎂合金沖壓成形性
之研究，2006鎂合金協會年會論文，p.139-143.
9. 王建義、蔡浩然、邱垂泓、陳世芳，AZ91D鎂合金之時效處理研 究，2006鎂合金協會年會論文，P. 69-71.
10. 蔡浩然、王建義、邱垂泓、陳世芳，AZ91D 擠型材之熱處理研 究，2006材料學會年會論文。
CURRICULUM VITAE
Chui-Hung Chiu
Contact Information
• Address: Rm.702, Bldg.52, 195, Sec.4, Chung Hsing Road, Chutung, Hsinchu, Taiwan
• Tel: +886-3-5914157
• E-mail: davy@itri.org.tw
Education
• Metallurgy Engineering, National Taipei Institute of Technology, (Sep 1985 - June 1988)
• M.S. in Material Science, Tatung Institute of Technology, (Sep 1994 - June 1996)
Current Positions
• Researcher, Industrial Technology Research Institute, Taiwan ( July 2002 - )