The localized corrosion of the two magnesium-aluminum alloys AM50 and AZ91 produced by a semisolid casting method was investigated under atmospheric corrosion conditions, in the presence of NaCl. Gravimetry confirmed the beneficial effect from ambient levels of carbon dioxide (CO2) in suppressing corrosion through the formation of magnesium hydroxy carbonates. Both 2D and 3D characterization revealed that ambient CO2 has a strong influence on the morphology and rate of localized corrosion. In CO2-free atmosphere, the alloys suffered localized corrosion resulting in clustered and interconnected cavities that extended deep into the material. In contrast, corrosion in the presence of ambient levels of CO2 (400 ppm) resulted in evenly distributed shallow corrosion sites. The results indicate that CO2 neutralizes the cathodic areas resulting in diminished cathodic activity and inhibiting NaCl(aq) droplet coalescence.

Subject
Scanning electron microscopy, Energy dispersive X-ray spectroscopy, Metal surfaces, Corrosion cells, Magnesium alloys, Sodium chloride, Dissolution, Acidity, Corrosion products, Film formation, Localized corrosion, Aluminum alloys, Alloys
Keywords:
atmospheric corrosion, casting, corrosion morphology, localized corrosion, magnesium-aluminum alloys, 3D imaging
© 2021, NACE International
2021
You do not currently have access to this content.