Adhesion Testing Methods for Electroplated Coatings
Thickness is useless without adhesion. Explore the destructive testing methods—from the Bend Test to the Thermal Shock Test—used to ensure your plating never peels.
The most fundamental requirement of any plated coating is that it stays on the part. If a layer of nickel or tin peels away, it doesn’t matter how thick or shiny it was—the part is a total failure.
Because “adhesion” is a measure of the atomic bond between the metal and the substrate, it cannot be measured non-destructively like thickness. To be sure it’s good, you have to try and break it.
Here are the industry standard adhesion tests per ASTM B571.
1. The Bend Test (The Workhorse)
The most common test for small parts and sheet metal.
- The Process: A plated part (or a sample coupon) is bent over a mandrel until it is folded 180° back on itself.
- The Goal: The metal coating will be under extreme tension on the outside of the bend and extreme compression on the inside.
- Failure: If the plating flakes, peels, or shows “lifting” at the bend, the adhesion is insufficient. Cracking is often acceptable (if the metal is brittle like hard chrome), but peeling is never allowed.
2. The Burnish / Scribe Test
Used for heavy coatings or parts that cannot be easily bent.
- The Process: A sharp tool is used to draw a grid pattern (cross-hatch) through the plating down to the base metal. The area is then aggressively rubbed with a smooth tool (burnished) or pulled with high-strength tape.
- Failure: If any of the squares of plating lift or peel away from the grid lines, the batch is rejected.
3. The Thermal Shock Test
Used for parts that will operate in extreme temperatures, such as engine or aerospace components.
- The Process: The plated part is heated in an oven (e.g., 250°\textC for 1 hour) and then immediately plunged into cold water.
- Failure: The rapid expansion and contraction will cause any weakly bonded areas to blister or bubble. This is the ultimate test for “latent” adhesion issues that might not show up at room temperature.
4. The Grind / Saw Test
Used primarily for heavy Hard Chrome or Electroless Nickel.
- The Process: The edge of the plated part is ground or sawed in a direction that tries to “push” the plating away from the substrate.
- Failure: If the plating separates from the base metal at the cut edge, the adhesion is poor.
At Platinex Industries, we perform daily adhesion verification on every production line to ensure our pre-treatment chemistry is perfectly tuned. Contact our quality team to learn about our rigorous testing protocols.