Types of Corrosion Resistant Metal Coatings

Types of Corrosion Resistant Metal Coatings

By Laura Davis, Manufacturing Technology Insights | Friday, January 08, 2021

Choosing good corrosion resistance is essential for a successful component design and manufacture.  

FREMONT, CA: In a broad range of industries, lightweight metals have emerged as the go-to alternative. In automotive, aerospace, and many consumer applications, metals like aluminum, titanium, and even magnesium have become vital. Combining their wealth, excellent strength-to-weight ratios, and flexibility means that they are a preferred choice for product engineers worldwide.

Even when untreated, some lightweight alloys give superior corrosion resistance, but it is unavoidable that surface treatment in a finished product will be required for performance, durability, and quality purposes. Magnesium is known for its low corrosion resistance. However, what is less well known is that it is equally vulnerable to some aluminum alloys and other high strength families containing copper or other transition metals.

Top 10 Corrosion Consulting/Service Companies  -  2020Anodizing

Anodization is the most common process of enhancing the corrosion resistance of aluminum. To attain security, it requires a four-step procedure. The first step includes immersing the material in a conductive solution bath, usually a low pH acid bath, and the alloy's attachment to the electrical circuit anode.

An oxidation reaction happens on the metal surface when an electrical current is applied, which allows the natural oxide on the surface metal to thicken, forming a protective outer layer of aluminum oxide. By increasing the coating time, the thickness can be modified, thereby providing a flexible range of applications:

It can give good pretreatment for paint or subsequent coatings when applied gently,

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When dyed, complex color effects can be achieved.

It is translucent when added thinly (typically <20μm) when applied thinly and maintained the metallic aesthetic.

PEO

The use of plasma discharges to turn the metallic surface of light metals includes Plasma Electrolytic Oxidation (PEO). It forms an oxide layer of adhesive that is both hard and dense. In a bath, components are submerged, and an electrical current is being used to expand a uniform oxide layer on the surface. Over a three-stage process, PEO takes place:

Modification of the resulting layer by plasma discharge

Oxidation of the substrate (as occurs in the anodizing process)

Co-deposition of the elements from the electrolyte into the coating

For lightweight metals like aluminum, titanium, and magnesium, PEO forms hard, dense, and wear-resistant coatings. PEO shapes coatings with higher hardness, chemical passivity, and an advantageous, uneven pore structure that develops high strain tolerance and better adhesion when directly compared to anodized coatings.

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