Coating bonding strength refers to the bonding strength between the coating and the base metal, that is, the force required to peel off the coating from the base metal per unit area.

The poor bonding strength of the coating is mostly caused by poor external treatment before plating. In addition, the plating solution composition and process specifications are inappropriate or the thermal expansion coefficients of the base metal and coating metal are different, all have a significant impact on the bonding strength of the coating.

Qualitative methods are usually used to evaluate the bonding strength between the coating and the base metal. The workshop qualitative measurement method is based on the difference in physical and mechanical properties of the coating metal and the base metal. That is when the sample is subjected to uneven deformation, thermal stress and the direct action of external force, the coating is checked for poor bonding. The specific method can be selected according to the type of plating and the plated parts: (1) bending test, (2) file test, (3) scratch test, (4) thermal shock test.