Hostname: page-component-848d4c4894-8bljj Total loading time: 0 Render date: 2024-06-17T14:36:09.122Z Has data issue: false hasContentIssue false
  • English
  • Français

Effect of heat treatment on anodization and electrochemical behavior of AZ91D magnesium alloy

Published online by Cambridge University Press:  03 March 2011

Houng-Yu Hsiao  and
Wen-Ta Tsai
Houng-Yu Hsiao
Affiliation:
Department of Materials Science and Engineering, National Cheng Kung University,Tainan, Taiwan 701, Republic of China
Wen-Ta Tsai*
Affiliation:
Department of Materials Science and Engineering, National Cheng Kung University,Tainan, Taiwan 701, Republic of China
*
a)Address all correspondence to this author. e-mail: wttsai@mail.ncku.edu.tw
Get access

Abstract

The anodic films formed on AZ91D magnesium alloy after heat treatment were analyzed and their electrochemical properties were investigated. The results showed that the cooling rate had a significant influence on the microstructure evolution of the AZ91D magnesium alloy after solution heat treatment at 440 °C for 20 h in N2 atmosphere. A single-phase microstructure was observed when the alloy was quenched in water after solution heat treatment. However, a duplex structure consisting of both α and β phases was found if the solution-annealed alloy was cooled in air. The differences in microstructure of the heat treated AZ91D magnesium alloy gave rise to a significant change in the property of the anodic film formed in 3 M KOH + 0.21 M Na3PO4 + 0.6 M KF + 0.15 M Al(NO3)3 electrolyte. During the early stage of anodization, for the as-cast alloy, inhomogeneous anodic films were formed exhibiting relative rough surface appearances. A rather smooth anodic film was formed for the solution-annealed AZ91D magnesium alloy either followed by air cooling or water-quenched. The surface and cross section appearance was almost the same regardless of the prior heat treatment after anodizing for 20 min. The corrosion resistances of the various anodized AZ91D magnesium alloy were evaluated and compared by employing electrochemical impedance spectroscopy (EIS). The results demonstrate that the anodic film formed on the water-quenched AZ91D magnesium alloy had a slightly higher polarization resistance than that formed on the as-cast alloy. The highest polarization resistance of anodic film was found for that formed on annealed and air-cooled alloy. The presence of Al-rich β phase on the surface gave rise to the formation of a more protective anodic film which consisted of a great amount of Al2O3.

Keywords

AnnealingBarrier layerMicrostructure
Type
Articles
Information
Journal of Materials Research , Volume 20 , Issue 10 , October 2005 , pp. 2763 - 2771
Copyright
Copyright © Materials Research Society 2005

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

REFERENCES

1Lunder, O., Lein, J.E., Aune, T.K. and Nisancioglu, K.: The role of Mg17Al12 phase in the corrosion of Mg alloy AZ91. Corrosion 45, 741 (1989).Google Scholar
2Song, G., Atrens, A., Wu, X. and Zhang, B.: Corrosion behavior of AZ21, AZ501 and AZ91 in sodium chloride. Corros. Sci. 40, 1769 (1998).Google Scholar
3Song, G., Atrens, A. and Dargusch, M.: Influence of microstructure on the corrosion of diecast AZ91D. Corros. Sci. 41, 249 (1999).CrossRefGoogle Scholar
4Ambat, R., Aung, N.N. and Zhou, W.: Evaluation of microstructural effects on corrosion behavior of AZ91D magnesium alloy. Corros. Sci. 42, 1433 (2000).CrossRefGoogle Scholar
5Aung, N.N. and Zhou, W.: Effect of heat treatment on corrosion and electrochemical behavior of AZ91D magnesium alloy. J. Appl. Electrochem. 32, 1397 (2002).Google Scholar
6Song, G., Bowles, A.L. and John, D.H. St.: Corrosion resistance of aged die cast magnesium alloy AZ91D. Mater. Sci. Eng. A 366, 74 (2004).Google Scholar
7Ono, S., Osaka, T., Asami, K. and Masuko, N.: Oxide films formed on magnesium and magnesium alloys by anodizing and chemical conversion coating. Corros. Rev. 16, 175 (1998).CrossRefGoogle Scholar
8Khaselev, O. and Yahalon, J.: Constant voltage anodizing of Mg–Al Alloys in KOH–Al(OH)3 solutions. J. Electrochem. Soc. 145, 190 (1998).CrossRefGoogle Scholar
9Birss, V., Xia, S., Yue, R., Rateick, R.G.R. and Jr., : Characterization of oxide films formed on Mg-based WE43 alloy using AC/DC anodization in silicate solutions. J. Electrochem. Soc. 151, B1 (2004).Google Scholar
10Xia, S., Yue, R., Rateick, R.G.R.Jr., and Birss, V.: Electrochemical study of AC/DC anodized Mg alloy in NaCl solution. J. Electrochem. Soc. 151, B179 (2004).Google Scholar
11Hsiao, H.Y. and Tsai, W.T.: Characterization of anodic films formed on AZ91D magnesium alloy. Surf. Coat. Technol. 190, 299 (2005).CrossRefGoogle Scholar
12Ono, S., Asami, K. and Masuko, N.: Mechanism of chemical conversion coating film growth on magnesium and magnesium alloys. Mater. Trans. 42, 1225 (2001).Google Scholar
13Bag, A. and Zhou, W.: Tensile and fatigue behavior of AZ91D magnesium alloy. J. Mater. Sci. Lett. 20, 457 (2001).CrossRefGoogle Scholar
14Takaya, M.: Anodizing of magnesium alloys in KOH–Al(OH)3 solutions. Aluminum 65, 1244 (1989).Google Scholar
15Fukushi, S. and Takaya, M.: Springer Series in Chemical Physics. Secondary ion mass spectrometry: SIMS V: Proceedings of the 5th International Conference, Washington, D.C. 44, 400 (1985).Google Scholar
16Ono, S., Asami, K., Osaka, T. and Masuko, N.: Structure of anodic films on magnesium. J. Electrochem. Soc. 143, L62 (1996).Google Scholar
17Khaselev, O., Weiss, D. and Yahalon, J.: Anodizing of pure magnesium in KOH-aluminate solutions under sparking. J. Electrochem. Soc. 146, 1757 (1999).CrossRefGoogle Scholar
18Hsiao, H.Y. and Tsai, W.T.: Anodization of AZ91D magnesium alloy insilicate-containing electrolytes. Surf. Coat. Tech. 199, 127 (2005).CrossRefGoogle Scholar
19Boukamp, B.A.: A package for impedance/admittance data analysis. Solid State Ionics, 18 & 19,136 (1986).Google Scholar