Beyond Anodizing
Advanced Aluminum Surface Treatments for Engineering Applications
Introduction
When most people think of surface treatments for aluminium, they immediately think of anodising—and for good reason. Anodising is a surface treatment process that enhances the properties of metals, particularly aluminium. Through an electrochemical process, an oxide layer is formed on the surface, offering improved corrosion resistance, wear resistance, and aesthetic appeal.
However, anodising isn't the only option, and in some precision engineering applications, it's not the optimal one. Anodised surfaces can be porous, may impact electrical conductivity, and can cause dimensional changes that affect performance—issues we’ve explored in a separate article.
For industries that demand tighter tolerances, lower friction, or high-performance coatings in dynamic environments, alternative surface treatment technologies exist that offer significant advantages. In this article, we explore two advanced aluminium coating processes that go beyond standard anodising: Dimensionally Stable Coating and Ematalising.
1. Dimensionally Stable Coating – Precision Despite Protective Layers
A dimensionally stable coating refers to a material's ability to resist changes in size due to mechanical or thermal stress. In surface treatment, it also implies maintaining dimensional accuracy even after applying coatings that typically increase component size.
Protective coatings—such as anodising, painting, or chemical treatments—tend to add material to the surface. For high-precision parts, even a few microns of added thickness can exceed allowable tolerances and compromise function, alignment, or fit.
To maintain precise dimensions, manufacturers apply dimensionally stable coatings through one or both of the following methods:
Pre-compensation during machining: Components are machined slightly undersized in key areas to anticipate the known thickness of the coating. This requires precise process knowledge and control.
Post-coating adjustment: After coating, selective removal methods—like chemical etching or precision grinding—are used to bring the component back within specification.
Key Applications & Environments:
Aerospace actuator systems
Optical and measurement instruments
Medical devices
Robotic joints and high-speed automation
2. Ematalising – Low-Friction, High-Precision Coatings
Ematalising, also known as Ematal anodising, is a specialised anodic surface treatment developed for aluminium and its alloys. Unlike standard anodising, which relies on sulfuric acid-based electrolytes, Ematal uses an electrolyte solution containing titanium and zirconium that produce a much denser and more uniform oxide layer. The result is a compact, glaze-like coating that is extremely hard, nearly non-porous, and exhibits a naturally low coefficient of friction.
This makes Ematalising particularly well suited for components exposed to sliding contact or flowing media. It’s commonly used in plain bearings, hydraulic and pneumatic systems, valve housings, and nozzles—areas where friction reduction and wear resistance are critical. The coating achieves a dry coefficient of friction below 0.1 and offers excellent surface hardness, comparable to quartz or topaz on the Mohs scale (7–8). Unlike many other coatings, Ematal forms evenly on complex geometries, including threads, bores, and narrow internal passages, making it ideal for intricately machined parts.
Beyond wear resistance and friction control, Ematal also provides excellent electrical and thermal insulation. This makes it useful in mechatronic and electromechanical assemblies where electrical isolation is required. Aesthetically, Ematal coatings typically appear light grey to bronze in color, though on high-silicon aluminium alloys, they can be rendered in matte black for functional or design-driven applications.
Applications & Environments:
Pneumatic and hydraulic systems
Aerospace actuators and precision linkages
Valve housings and nozzle blocks
Cleanroom automation and sensor housings
Miniature moving assemblies where lubrication is limited
Conclusion
While anodising is the most commonly encountered surface treatment for aluminium, technologies like dimensionally stable coatings and Ematalising remain relatively underutilized and less frequently discussed in typical manufacturing conversations. These advanced processes are not always on the radar of many engineers and manufacturers, yet understanding their unique capabilities can significantly broaden your toolkit when specifying and designing aluminium components.
By being aware of these specialized coatings, engineers can better address critical challenges such as maintaining tight dimensional tolerances, reducing friction in dynamic assemblies, and extending component lifespan in demanding environments. This deeper knowledge enables more informed decisions, helping to optimize performance, reduce rework, and ultimately deliver higher-quality products. Expanding your surface treatment vocabulary beyond conventional anodising opens the door to innovative solutions that can elevate your engineering outcomes and give you a competitive edge in component design and manufacturing.
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