The Problem with Electroplating
Electroplating is a major cause of hydrogen embrittlement. Some hydrogen is generated during the cleaning and pickling cycles, but by far the most significant source is cathodic inefficiency, which is followed by sealing the hydrogen in the parts. Baking is often performed on high-strength parts to reduce this risk, and the ASTM, issued a specification for baking cycles, Standard Guide for Post-Coating Treatments of Steel for Reducing the Risk of Hydrogen Embrittlement (B850), as shown to right. For the production plater, having to remove the parts from the production line to bake — followed by a separate chromating or passivating process — is a laborious undertaking.
Zinc Deposit
Steel Substrate
Why Mechanical Plating?
Mechanically deposited zinc coatings consist of small platelets formed from the mechanical action of glass beads on fine (3 to 7 microns) zinc dust particles. The platelets thus formed are "cold-welded" to the substrate and to each other. The porous (approximately 80 percent density) deposit can therefore effuse the hydrogen that would otherwise produce hydrogen embrittlement.
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How Much Baking Do Electroplated Parts Need? (ASTM B850)
| Tensile Strength (MPa) |
Tensile Strength (000 psi) |
Rockwell Hardness HRc |
Post-Plate Bake (@190°-220°C or 374°-428°F) |
| 1,700-1,800 |
247-261 |
49-51 |
22+ |
| 1,600-1,700 |
232-247 |
47-49 |
20+ |
| 1,500-1,600 |
218-232 |
45-47 |
18+ |
| 1,400-1,500 |
203-218 |
43-45 |
16+ |
| 1,300-1,400 |
189-203 |
39-43 |
14+ |
| 1,200-1,300 |
174-189 |
36-39 |
12+ |
| 1,100-1,200 |
160-174 |
33-36 |
10+ |
| 1,000-1,100 |
145-160 |
31-33 |
8+ |
Source: ASTM B850, accordingto Section 6.2 - Steels of actual tensile strength below 1000 MPa, Heat treatment after plating is not essential.
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