Chromate-Free Corrosion Protection Strategies for Magnesium Alloys-A Review: Part II-PEO and Anodizing.

Area of Science:

• Materials Science
• Corrosion Engineering
• Surface Engineering

Background:

• Hexavalent chromium (Cr(VI)) based protection systems for Mg alloys, while effective, pose significant toxicity and carcinogenicity risks.
• The need for safer, high-performance alternatives has driven research for over two decades.
• Current challenges include finding Cr-free replacements that match Cr(VI) efficacy without compromising safety, cost, or environmental impact, especially for the transportation industry.

Purpose of the Study:

• To review advancements in Mg alloy anodizing technologies, focusing on chromium-free alternatives.
• To explore the potential of Plasma Electrolytic Oxidation (PEO) as a superior corrosion protection method.
• To summarize factors influencing the performance of anodized coatings and their industrial applicability.

Main Methods:

• Review of traditional chromium-based anodizing processes.
• Analysis of emerging chromium-free alternatives, particularly Plasma Electrolytic Oxidation (PEO) using organic electrolytes.
• Examination of processing parameters: electrolyte composition, additives, voltage/current regimes, and post-treatment sealing.

Main Results:

• Plasma Electrolytic Oxidation (PEO) effectively forms a protective ceramic-like layer on Mg alloys, significantly enhancing corrosion resistance.
• Optimizing PEO fabrication conditions allows for the development of Cr-free coatings that meet stringent industrial performance requirements.
• Anodizing, especially PEO, presents a viable pathway to replace hazardous Cr(VI) systems.

Conclusions:

• Plasma Electrolytic Oxidation (PEO) is a leading chromium-free technology for enhancing Mg alloy corrosion resistance.
• Careful control over processing parameters enables the tailoring of PEO coatings to meet demanding industrial specifications.
• The development of PEO and similar technologies addresses health, environmental, and performance needs for Mg alloy surface treatments.