It’s very likely that when people hear the terms; chrome plating, chromium plating, or even just “chrome” what probably comes to mind is the visualization of a shiny metal surface, but does it only serve an aesthetic purpose? If not, what other purpose does it serve?
When unalloyed, Chromium has a relative high hardness and great corrosion resistance, which make it a great ally for surface coating applications. As a matter of fact, it is currently the most popular metal coating, with a durability that is hardly paralleled.
Is all chrome plating the same?
Short answer: no. There are basically two types of chrome plating – Decorative and Hard Chromium Plating. Each has a different set of properties, which offer a variety of benefits, and subsequently have different applications. Let’s take a closer look at each.
Bright/Decorative Chromium Plating
Its name is self-explanatory: this type of chrome plating is very popular because it’s very aesthetically pleasing. However, it does more than add a nice look to the element, it also provides a very durable and corrosion-resistant layer.
Characteristics & Benefits
- It requires nickel plating (up to two layers) prior to the application of the chromium plating.
- While it’s called “chromium plating”, the underlying layer of nickel is what provides this coating with practically all of its trademark reflectivity, smoothness, and much of its corrosion resistance.
- Nickel adheres extremely well to copper, so it’s not uncommon to have copper and nickel plating before the final layer of chromium is added. If done right, the effective combination of the three layers offers possibly the best balance between corrosion protection, wear protection, adherence, and aesthetics.
- This chrome plating is applied as a very thin layer, with a thickness from 0.002 and 0.02 mils (0.05 – 0.5 µm), and more commonly present in 0.005 to 0.01 mils (0.13 to 0.25 µm) thick layers.
- The most common base materials include plastic, aluminium, copper alloys, zinc alloys, and steel.
- Decorative chromium plating application is very popular in the automotive industry, in which durability, corrosion resistance, and aesthetics are all greatly valued. It is not uncommon to see a decorative chromium plating on elements of both cars and motorcycles; such as rims, engine components, exhausts, and more.
- It is also a great fit for kitchen utensil design requirements.
- Other common applications can be seen in premium tools and taps.
Hard/Engineered Chromium Plating
Also known as plain ‘hard chrome’, ‘industrial chrome’, or ‘engineered chrome’, it is usually thicker than decorative chrome plating, and its applications are more engineering-oriented.
Characteristics & Benefits
- It features great hardness, measuring up to 65 to 69 HRC (which will also depend on the base metal’s own hardness).
- It has great lubricity, which combined with its hardness, makes it one of the prime engineering choices for friction reduction, durability enhancement through abrasion resistance (as well as wear resistance in general), and prevention of galling.
- It expands chemical inertness, which is excellent if the inclusion of a broader set of conditions, in particular oxidation resistance, is desired.
- As mentioned, its coating is usually applied in greater thickness than the decorative counterpart, achieving up to 3.9 mils (100 µm) or thicker, when extreme wear resistance is required. However, the standard thickness for this chromium plating ranges from .78 to 1.57 mils (20 to 40 µm).
- It’s also used in the automotive industry, but for critical engineering applications: shock absorbers, cylinders, and other components that are prone to work under high cycles over extended periods of time. Such components receive hard chrome plating in order to meet durability and lubricity requirements.
- It has a wide variety of applications in the aerospace industry as well. Some hard chrome plated components in this industry are: landing gear and aluminium piston heads, in order to provide an optimal performance while keeping weight minimal; actuator elements, so as to prevent wear and extend their service life.
- Gears are usually hard chrome plated because of the galling-prevention and lubricity benefits this coating provides. This is translated into enhanced performance and the extension of service life in low-friction applications.
- It’s also often used in worn parts as filling material in order to restore original dimensions.
Chrome plating is a prime metal coating. It serves an immense range of needs for an equally vast range of industries; where it remains a reliable choice thanks to Chromium’s particular combination of properties.