本研究藉由改變溶液組成、溶液的pH值以及不同熱處理條件等實驗變因，探討壓鑄AZ91D鎂合金的顯微組織對其腐蝕行為之影響。實驗中所採用的測試溶液分別為3.5 wt % NaCl（不同pH值）以及1M NaOH（pH = 13.74）水溶液。熱處理條件分別為壓鑄AZ91D鎂合金經410℃持溫20小時後空冷以及經440℃持溫20小時後水冷。
實驗結果顯示，壓鑄AZ91D鎂合金在3.5 wt % NaCl水溶液中( pH = 6.1 )會發生局部腐蝕，其中腐蝕會在a相中鋁含量較少、矽含量較多，以及在鄰近b相的a相中，和含有鋁錳析出物的位置發生。其中b相在此測試環境中相對上比a相具有較佳的耐蝕性。從腐蝕型態分析，AZ91D鎂合金顯微組織中b相具有阻礙a相腐蝕延伸的作用。此外，當合金中有較多且分佈較連續的b相時，開路電位值會稍微提高，而腐蝕電流密度會降低。
在酸性的環境下( pH = 2.0 ) ，AZ91D鎂合金所含有之a相及b相（Mg17Al12介金屬化合物）腐蝕程度相近 ; 而在中性以及鹼性的環境中（ pH = 6.1，pH = 12.0 ）b相比a相具有較佳的耐蝕性。電化學試驗結果顯示，在3.5 wt % NaCl水溶液中，隨著pH值提高，AZ91D 鎂合金表面的鈍化膜將較為穩定。
壓鑄AZ91D鎂合金在1 M NaOH水溶液( pH = 13.74 )中並不會有蝕孔產生，a相以及b相皆有明顯的鈍化現象。以低掠角XRD分析表面鈍化膜的結構，結果包含有Mg(OH)2、Mg4Al2(OH)14 × H2O以及Mg2Al(OH)7。

The influence of microstructure on the corrosion behavior of heat treated die-cast AZ91D magnesium alloy was investigated in various aqueous solutions. Heat treatment of die-cast AZ91D was performed at 410 °C for 20h followed by cooling in air or 440 °C for 20h followed by quenching in ice water. The aqueous solutions employed were 3.5 wt % NaCl solutions with different pH as well as 1 M NaOH solution.
The results showed that localized corrosion occurred on the surface of the die-cast AZ91D in 3.5 wt % NaCl solution with pH = 6.1. The regions with low aluminium or high silicon concentration were prone to corrosion. Localized corrosion was also found to occur in the vicinity around intermetallic precipitate. The experimental results revealed that b phase was more corrosion resistant than a phase in the neutral 3.5 wt % NaCl solution. Morphological examination observation revealed that b phase in AZ91D magnesium alloy could act as a barrier of corrosion extension from a phase. The electrochemical testing results indicated that the more amount of b phase present in the AZ91D alloy, the more noble open circuit potential ( OCP ) could be observed. A decrease in anodic current density was also noticed as the b content in the AZ91D magnesium alloy was increased.
In acidic solution ( pH = 2.0 ) both the matrix phase ( a ) and the precipitates ( b, Mg17Al12, intermetallic compound ) were severely corroded. However, in neutral and in alkaline solutions ( pH = 6.1, pH = 12.0, respectively ), b phase had a higher resistance to corrosion than a phase. The electrochemical testing results also indicated that the passive film formed on AZ91D become more stable in 3.5 wt % NaCl solution as its pH was increased.
Pits were not observed on the surface of AZ91D in 1 M NaOH solution ( pH = 13.74 ). Both a phase and b phase could be passivated. The results of glacing angle XRD analyses revealed that the passive films formed on the surface were composed of Mg(OH)2, Mg4Al2(OH)14 · H2O and Mg2Al(OH)7.

參考文獻
1. 蔡幸甫，鎂合金在電子產品上的應用與產業概況，工業材料，p.62，1999.08。
2. 蔡幸甫，筆記型電腦應用鎂合金的幾個重大理由，工業材料，p.116，1999.10。
3. 王文梁，鎂合金於國外汽車產業之應用狀況與研發趨勢，金屬工業，p.58，2000.05。
4. 廖芳俊，鍛造用Mg-Al-Zn系鎂合金熔銲製程之探討，工業材料，p.169，2001.06。
5. 蔡幸甫，輕金屬產業發展狀況及商機，工業材料，p.77，2001.06。
6. 邱垂泓、楊智超，鎂合金成型技術之發展趨勢，工業材料，p.84，2001.06。
7. G. L. Makar and J. Kruger, Corrosion of magnesium, International Materials Reviews, Vol.38, No.3, 1993.
8. Rajan Ambat, Naing Naing Aung and W.Zhou, Evaluation of microstructural effects on corrosion behavior of AZ91D magnesium alloy, Corrosion Science, Vol.42, p.1433, 2000.
9. Guangling Song, Andrej Atrens, Xianliang Wu and Bo Zhang, Corrosion behavior of AZ21, AZ501 and AZ91 in sodium chloride, Corrosion Science, Vol.40, p.1769, 1998.
10. Guangling Song, Andrej Atrens and Matthew Dargusch, Influence of microstructure on the corrosion of diecast AZ91D, Corrosion Science, Vol.41, p.249, 1999.
11. Nadine Pebere, Christian Riera and Francis Dabosi, Investigation of magnesium corrosion in aerated sodium sulfate solution by electrochemical impedance spectroscopy, Electrochimica Acta, Vol. 35, p.555, 1990.
12. S. K. Das and L. A. Davis, High performance aerospace alloys via rapid solidification processing, Mater. Sci. Eng. , Vol.98, p.1, 1988.
13.楊智超，鎂合金材料特性及新製程發展，工業材料，p.72，1999.08。
14.鎌土重晴，小島陽原著，陳永璋譯，鎂合金之熱處理，金屬熱處理，p.72，1999。
15. Polmear I. J. , Mganesium alloys and applications, Materials Science and Technoogy , Vol.10, p.1, 1994.
16. J. H. Nordlien, S. Ono, N. Masuko and K. Nisancioglu, A TEM investigation of naturally formed oxide films on pure magnesium, Corrosion Science, Vol.39, p.1397, 1997.
17. M. Avedesian and Hugh Baker, Magnesium and magnesium alloys, ASM Specialty Handbook, 1999.
18. Geneviève Baril, Christine Blanc and Nadine Pebebe, Influence of microstructure on the corrosion behavior of two magnesium alloys by EIS, Electrochemical Society Proceedings, Vol.23, p.166, 2000.
19. O. Lunder, T. Kr. Aune, K. Nisanciogl, Effect of manganese additions on the corrosion behavior of mould-cast magnesium ASTM AZ91, Corrosion, Vol.43, p.291, 1987.
20. Rajan Ambat, Naing Naing Aung and W.Zhou, Studies on the influence ofchloride ion and pH on the corrosion and electrochemical behaviour of AZ91D magnesium alloy, Journal of Applied Electrochemistry, Vol.30, p.865, 2000.
21. W. M. Chan, F. T. Cheng, L. K. Leung, R. J. Horylev and T. M. Yue, Corrosio behaviour of magnesium alloy AZ91 and its MMC in NaCl solution, Corrosion Reviews, Vol.16, p.43, 1998.
22. M. Pourbaix, Atlas of Electrochemical Equilibria in Aqueous Solution, NACE, Houston, TX, USA, 1974.
23. O. Lunder, J. E. Lein, T. Kr. Aune and K. Nisancioglu, The role of Mg17Al12 phase in the corrosion of Mg alloy AZ91, Corrosion, Vol.45, p.741, 1989.
24. C. B. Baliga and P. Tsakiropoulos, Development of corrosion resistant magnesium alloys Part 2 Structure of corrosion products on rapidly solidified Mg-16Al alloys, Materials Science and Technology, Vol.9, 1993.
25. P. Schmutz, S. Virtanen, L. Kocher and P. J. Uggowitzer, Corrosion behavior of novel Mg-Al alloys produced by means of the new rheocasting (NRC) process, Electrochemical Society Proceedings, Vol.23, p.156, 2000.
26. G. L. Marker, J. Kruger, and K. Sieradzki, Repassiviation of rapidly solidified magnesium-aluminum alloys, J. Electrochem. Soc. , Vol.139, p.47, 1992.
27. D. Daloz, C. Rapid, P. Steinmetz, and G. Michot, Corrosion inhibition of rapidly solidified Mg-3﹪Zn-15﹪Al Magnesium alloy with sodium carboxylates, Corrosion, Vol.54, p.444, 1998.
28. K. Nisancioglu, O. Lunder and T. Aune, Corrosion mechanisms of AZ91 magnesium alloy, Proc 4774 World Magnesium Conference, Cannes, p.43, 1990.
29. David L. Hawke, Galvanic corrosion of magnesium, SDCE 14th International Die Casting Congress and Exposition, Toronto, 1987.
30. O. Lunder, K. Nisancioglu and R. S. Hanses, Corrosion of die cast Magnesium-Aluminium alloys, SAE Technical Paper#930755, 1993.
31. H. Okamoto, J. Phase Equilibria, Vol.19, p.598, 1998.
32. H. Okamoto, J. Phase Equilibria, Vol.15, p.129, 1994.
33. N. U. Deshpanade, K. K. Ray, and A. K. Mallik, J. Alloy Phase Diagrams, India, Vol2, p.108, 1986.
34. G. Song, A. Atrens, D. Stjohn, J. Nairn and Y. Li, The Electrochemical Corrosion of Pure Magnesium in 1N NaCl, Corrosion Science, Vol.39, p.855, 1997.
35. O. Lunder, J. E. Lein, S. M. Hesjevik, T. Kr. Aune, and K. Nişancioğlu, Corrosion morphologies on magnesium alloy AZ91, Werkstoffe und Korrosion, Vol.45,p.331,(1994).
36. T. Beldjoudi, C. Fiaud and L. Robbiola, Influence of homogenization and artificial aging heat treatments on corrosion behavior of Mg-Al alloys, Corrosion Science, Vol.49, p.738, 1993.