Effect of surface-pretreatment on adhesive strength of hard chromium plating.

Testing the adhesion between chromium plating and the base metal involves many difficulties, and the conventional test is too inaccurate to permit analysis of adhesion. For this reason an improved adhesion test, based on the drawing method developed by R. A. F. Hammond et al., was used to measure the strength of adhesion of chromium plating to the base metal. As the hydrogen overvoltage on the base metal surface to be plated seems to have a great effect on the mechanism of electrodeposition in chromium plating, it was measured to clarify the chemical characteristics of the surfaces, and the adhesion mechanism was considered.It is considered that the condition of the base metal surface to be plated influences the structure of the metal deposited at the first stage of the electrodeposition, and that the strength of adhesion of the plating to the base metal varies. If the base metal surface is etched by counterelectrolysis in the chromium plating bath just before plating, the base metal surface becomes favorable for plating. This etching process causes stronger adhesion of chromium plating to the base metal.