Yellow chromating - yellow zincing

Yellow chromating (colloquially referred to as “yellow zinc coating”) is a galvanic technique in which already galvanized surfaces are further refined through a yellow passivation. The result is a characteristic yellowish to golden surface that is both aesthetic and corrosion-inhibiting.

How Does Yellow Chromating Work?

1. Zinc Layer as the Basis
   First, the metal (e.g., steel) is galvanized (via electroplating or hot-dip galvanizing). This zinc layer serves as the foundation for the chromating process.
   
   
2. Chemical Post-Treatment
   This is followed by a passivation or chromating step. In the yellow variant, a special chromate solution produces the typical yellow to golden hue during the process.
   • In the past, chromium(VI) was often used, which is now widely regulated.
   • Modern systems increasingly rely on chromium(III) in order to meet environmental and health regulations.
     
     
3. Color Development
   The zinc surface reacts with ingredients in the chromate solution, forming a conversion layer (“chromate layer”). This layer enhances corrosion protection and creates the characteristic yellow-golden finish.

Why Use Yellow Chromating?

• Visual Upgrade: The yellow/golden surface is decorative and highly sought after in many sectors, for example for fittings, screws, or decorative parts.
• Additional Corrosion Protection: The chromate layer provides further protection against oxidation of the underlying zinc.
• Proven Standard: Yellow-chromated parts have been regarded as a benchmark for corrosion-resistant, aesthetically appealing surfaces for decades.

Chrom(VI)-Free vs. Chrom(VI)-Containing

• Chrom(VI)-Containing: Older, widespread methods that yield an intensely yellow color, but are heavily regulated or prohibited due to their harmful effects on health and the environment.
• Chrom(III)-Based: Much more environmentally and health friendly; the color intensity may be somewhat less pronounced, but these processes comply with current regulations and are continually being refined.

Advantages and Limitations of Yellow Chromating

Advantages

• Striking yellow/golden appearance
• Additional corrosion protection compared to plain zinc surfaces
• Versatile use, e.g., in the automotive industry, electronics, or home applications

Limitations

• Environmental constraints on chromium(VI)-based processes
• Limited to yellow/gold tones
• Quality highly dependent on pretreatment and the condition of the zinc layer

Conclusion

Yellow chromating is a post-treatment for galvanized surfaces, producing a yellow or golden chromate layer. This layer enhances corrosion protection while giving the workpiece a distinctive yellow/golden look. Previously carried out mainly with chromium(VI)-containing solutions, more and more chromium(III)-based systems are now in use in order to comply with environmental and health regulations. Despite certain differences in color intensity or processing parameters, yellow-chromated surfaces remain among the most popular and widely used finishes in galvanizing technology.