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The Application of Plasma Electrolyte Oxidation (PEO) to the Production of Corrosion
Resistant Coatings on Magnesium Alloys: A Review
R. O. Hussein, X. Nie and D. O. Northwood*
Magnesium alloys are widely used in the automotive, aerospace, electronics and sports/leisure
equipment industries because of their excellent physical and mechanical properties including low
density and high strength –to-weight ratio. However, magnesium is a highly reactive metal and
requires surface modification using protective coatings to obtain adequate environmental
resistance to corrosion and wear. Several techniques have been used for the surface engineering
of Mg alloys including anodizing, conversion coatings, electrochemical plating, physical vapor
deposition (PVD) coatings and organic coatings. Plasma electrolyte oxidation (PEO), which
evolved from the conventional anodizing process, has emerged as one of the most effective ways
of improving corrosion resistance. As is the case for all surface engineering technologies, the
successful development of PEO coatings is dependent on adequate substrate pretreatment
together with choice, and control, of electrolyte composition and process parameters. In this
paper we will review the effects of processing parameters (DC, AC, current density, voltage,
current mode, duration, temperature) magnesium alloy substrate and chemical composition of
electrolyte on the coating morphology and composition, and ultimately the corrosion resistance
of coated Mg-alloys. The review will also examine some new developments which involve the
codeposition of materials such as polymers, within the PEO layers to produce composite coatings
with much improved corrosion resistance.