Protecting Light Metal Alloys Using a Sustainable Plasma Electrolytic Oxidation Process

Area of Science:

• Materials Science
• Surface Engineering
• Electrochemistry

Background:

• Low-density metals like magnesium (Mg) and aluminum (Al) alloys are crucial for lightweight engineering but suffer from poor corrosion resistance and tribology.
• Traditional plasma electrolytic oxidation (PEO) processes often involve energy-intensive methods and toxic electrolytes, limiting their environmental sustainability.
• Current PEO techniques for composite coatings typically require nanoparticle additions or post-treatments, adding complexity and cost.

Purpose of the Study:

• To develop a versatile, environmentally friendly, single-step PEO process for Mg and Al alloys.
• To investigate the effects of in situ nitridation on the properties of PEO coatings.
• To evaluate the mechanical behavior and corrosion resistance of the novel PEO-treated surfaces.

Main Methods:

• A novel PEO process utilizing organo-silicate electrolytes enriched with nitrogen-containing solutions was employed.
• Uniform, adherent, and porous oxide coatings (approx. 6 μm thick) were produced on AZ80 and Al6061 alloys within 15 minutes.
• Coating properties were compared between those treated with and without nitrogen-containing electrolytes to assess nitridation effects.

Main Results:

• The single-step PEO process successfully generated uniform, adherent, and porous coatings on both alloys.
• Coatings exhibited multilayered, basalt-like topographies composed of metal oxides and metal silicates.
• Alloys treated with nitrogen-containing electrolytes showed the presence of oxynitrides and exhibited enhanced mechanical properties.
• Corrosion resistance was comparable to traditional PEO coatings, though nitridation showed a slight negative impact.

Conclusions:

• The developed PEO process offers an environmentally friendly and efficient method for surface passivation of light metals.
• In situ nitridation enhances mechanical properties of PEO coatings, creating mechanically resilient surfaces.
• Further research is needed to optimize corrosion resistance for nitride-containing PEO coatings.