Journal
CORROSION
Volume 75, Issue 6, Pages 668-679Publisher
NATL ASSOC CORROSION ENG
DOI: 10.5006/3025
Keywords
aluminum coating; corrosion resistance; magnesium alloys; thermal spraying; warm spraying
Funding
- National Centre of Research and Development in Poland within the LEADER V programmer Grant [003/097/L-5/13/NCBR/2014]
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The corrosion resistance of aluminum coatings on Mg alloy (AZ91E) substrate was investigated in 3.5% NaCl solution. The Al coatings were deposited using a warm spraying (WS) method under three different nitrogen flow rates (NFR): 1.0 m(3)/min, 1.5 m(3)/min, and 2.0 m(3)/min. The decrease of NFR during WS led to a decrease in the porosity of WS coatings from about 2.0% down to 0.5% and an increase in oxygen content from 0.24% up to 0.85%. The Al coating with the lowest porosity and the highest oxygen content exhibited the lowest current density in the passive range, highest breakdown potential during anodic polarization, and repassivation behavior. The impedance measurements revealed that this Al coating effectively protected the Mg substrate during 14 d of immersion in the test solution as its resistance remained four orders of magnitude higher (11,266 Omega.cm(2)) when compared to bare substrate (similar to 70 Omega.cm(2)). The microscopic observations confirmed that the coating remained consistent and well bonded to the substrate, and no corrosion products layer on coating/substrate interface was formed, indicating that the electrolyte did not penetrate through the coating. The higher porosity leads to faster degradation of the coatings formed under higher NFR.
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