Zinc Phosphate of Brazed Steel Parts
What is causing etching of tungsten carbide and copper alloy braze materials after zinc phosphating?
Q. We often use a zinc phosphate treatment on our steel parts (corrosion protection for oilfield parts) and have recently tried doing so on a 4140 steel part that has tungsten carbide inserts brazed to the steel with a copper-based braze alloy. Both the tungsten carbide material and the braze material surfaces are badly etched after this process. Can I assume the copper (braze) and cobalt in the tungsten carbide are being attacked?—M.B.
A. The zinc phosphate process is primarily only applicable to ferrous substrates. There are a few exceptions, but this is generally the case. I know that the zinc phosphate process is not applicable to copper-based alloys. I do not have experience with the tungsten carbide material that you mentioned but would also expect that it would not be compatible with a zinc phosphate formulation. The acidic nature of the typical bath would probably tend to attack the carbide in this alloy.
Related Content
-
Pretreatment for Painting
Better adhesion, enhanced corrosion and blister resistance, and reduced coating-part interactions make pretreatment a must.
-
Corrosion Resistance Testing for Powder Coating
Salt spray can be useful to help compare different pretreatment methods and coatings but it does not tell us much about the corrosion resistance of a part over time in the field. Powder coating expert Rodger Talbert offers insights into how to get a better idea of how to improve a part’s corrosion resistance in the real world.
-
Alkaline Cleaning Guide
Gregg Sanko, Senior Chemist, Oakite Products, Inc. provides an overview of the alkaline cleaning process.