What Causes Electroplated Coatings to Flake or Peel?

Poor adhesion is a common problem that can negatively impact the performance and longevity of an electroplated coating. Improper adhesion often takes the form of flaking, which occurs when the coating lifts, separates and peels away from the surface of the substrate. This results in large, bare or nearly bare areas that are no longer adequately protected by the coating. Pieces of a flaked coating are typically brittle in composition and are characterized by long, distinct edges.

Exploring the Causes of Flaking

Flaking can occur for a variety of reasons:

• Inadequate surface activation: Activation refers to the removal of the oxide layer that is present on the surface of most metals. Proper surface treatment prior to electroplating will eliminate oxides, as well as any remaining salt, soap, alkali or acid residues from cleaning products that can inhibit coating adhesion.
• Excessive coating thickness: Some platers mistakenly believe that a thicker coating will provide greater protection for the substrate. However, a coating that is too thick can become brittle and ultimately begin to “flake off” when the part is struck during assembly, or collides with a heavy object during transport.
• Current interruptions during plating: Interruption of the electric current or a broken electrical contact during plating can lead to flaking and other adhesion issues. If the electrical source is interrupted or turned off for an extended period of time, it is advisable to re-start the plating process.
• Low bath temperature: It is imperative to maintain the appropriate bath temperature for the duration of the plating process. When using a larger plating tank, agitation of the electrolyte plating solution is often necessary to avoid stratification and maintain a consistent temperature.
• High bath contaminant levels: Plating baths containing excessively high levels of contaminants such as iron and trivalent can result in poor adhesion, which often takes the form of flaking or peeling.

Tests for Identifying Flaking

There are several tests that can indicate the presence of flaking in a plated part. One example is the bend test, where a sample is placed in a vise and repeatedly bent over a mandrel until failure of the base metal occurs. Examination of the part under magnification will reveal any evidence of flaking or peeling. Another option is the heat-quench test, which entails baking the part in an oven, then submersing it in room-temperature water for cooling. A visual inspection of the cooled part will reveal signs of flaking, blistering or other potential adhesion issues.

SPC has the metal finishing experience and expertise to choose and effectively apply the appropriate coating method that will resist flaking and other common adhesion problems. Contact us for more information or to schedule a metal finishing consultation today.