Surface alloying of AZ91E alloy by Al-Zn packed powder diffusion coating

Hirmke, J., Zhang, M. X. and St John, D. H. (2011) Surface alloying of AZ91E alloy by Al-Zn packed powder diffusion coating. Surface and Coatings Technology, 206 2-3: 425-433. doi:10.1016/j.surfcoat.2011.07.050

Author Hirmke, J.
Zhang, M. X.
St John, D. H.
Title Surface alloying of AZ91E alloy by Al-Zn packed powder diffusion coating
Journal name Surface and Coatings Technology   Check publisher's open access policy
ISSN 0257-8972
Publication date 2011-10-25
Sub-type Article (original research)
DOI 10.1016/j.surfcoat.2011.07.050
Volume 206
Issue 2-3
Start page 425
End page 433
Total pages 9
Place of publication Lausanne, Switzerland
Publisher Elsevier S.A.
Collection year 2012
Language eng
Formatted abstract
A new surface coating technique, namely packed powder diffusion coating (PPDC), for AZ91E magnesium alloy is reported. This new technique uses a powder mixture of aluminium and zinc as diffusion source and produces uniform and thick coatings at temperatures below 420 °C. Experimental results showed that zinc in the powder mixture significantly promotes the formation of intermetallic layers on the surface of the magnesium alloy at process temperatures between 350 °C and 413 °C, which is more than 50 °C lower than the previously reported processes. Depending on the temperature and the Zn-content in the powder, X-ray diffraction analysis identified three intermetallic phases and Mg(Al, Zn) solid solution that consist of the surface alloyed layer. The intermetallic compounds are τ-Mg32(Al,Zn)49, φ-Al5Mg11Zn4 and β-Mg17(Al,Zn)12. The hardness of the over 500 μm thick surface alloyed layers is up to four times higher than the substrate. Both the β-Mg17(Al,Zn)12 phase and the τ-Mg32(Al,Zn)49 phase show one to two order magnitude higher corrosion resistance than the α-phase (solid solution) and the φ-Al5Mg11Zn4 phase in 5% NaCl solution. A process parameter window for the layer thickness as well as a schematic model for the formation of the layer is proposed. The PPDC process is a promising technique that provides effective protection of AZ91E alloy from both wear and corrosion.
Keyword Surface alloying
Diffusion coating
Mg-Al-Zn intermetallic compounds
Magnesium alloy
AZ91 alloy
Cold Spray Coatings
Q-Index Code C1
Q-Index Status Confirmed Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: Official 2012 Collection
School of Engineering Publications
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