Poor Adhesion: Plating

Topics: Chromium, Metal, Zinc Pages: 3 (812 words) Published: September 15, 2011


Poor adhesion results in the chrome deposit separating from the substrate. This can occur as either peeling or blistering of the chromium layer, and can happen immediately as the part comes out of the bath, or later when it is put into service. Unfortunately, a viable nondestructive test for adhesion is not available. An inconclusive tests is to immerse the part in boiling water AP, until it is up to temperature, then immediately immerse it in cold water. Any adhesion weak spots will likely show up as blisters in the deposit. Most adhesion tests, done on trial parts, consist of abusively grinding a 45 degree notch in the deposit and examining the edges under a microscope for flaking. Adhesion testers are available, but are mostly used on test coupons and not on real parts. It is generally accepted, however, that if a plated part stands up to grinding stresses after plating then the adhesion is adequate. Poor adhesion is almost always a function of improper BP cleaning, reverse etching or activation. Possible causes of poor adhesion include: • Improper activation.

Proper activation of the base metal is important for deposit adhesion. Different base metals and hardness require different reverse etching times or activation steps. It’s therefore important to know the base metal being plated. • Improper cleaning.

Parts need to be properly cleaned BP to remove all traces of oils, organics and surface debris. Refer to both the Process Cycle and the Basic Cycle for suggestions. The best suggestion is to Dura Prep scrub, for smaller lot quantities, if no other remedies works. • Inadequate rinsing.

It is important that rinsing BP removes all traces of prior chemical films from the part. Plating on top of prior chemical films will cause poor adhesion. • Oils or Organics on Bath Surface.

Certain oils and organics can break down in the bath forming a...
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