Case Study: Solving Anodized Aluminum Color Issues

Introduction

In July 2023, an electronics manufacturer from Finland sent us an urgent order. They needed 50 pieces of aluminum 6061-T5 parts with hard anodizing. Their mechanical engineer emailed, “We need to finish this project through CNC machining and hard anodizing in a natural finish. Can you deliver the parts within two weeks?” The parts were sensor housings with uniform appearance and corrosion resistance.

Project Brief

Categories	Details
Client	Finnish Electronic Device Manufacturer
Processing	CNC Machining
Material	Aluminum 6061-T5
Surface Finishing	Hard anodized natural color
Problem	Hard anodizing led to color differences

The Problem: In-depth Analysis

As we started this machining project, we found that the first batch of the aluminum samples also had the color consistency issues. Some areas appeared light gray, while others were dark gray. We couldn’t meet the client’s visual quality standards for consumer-facing components. And then we conducted an in-depth analysis.

1. Hard Anodizing Aluminum Process Issues

Current distribution: Aluminum parts on fixture edges received over 25% higher current density than the center aluminum parts.
Stagnant zones in the tank led to ±4°C temperature fluctuations.
Improper Fixture design: Traditional racking could be easily shadow areas on curved surfaces

2. Material Factors in 6061-T5 Aluminum CNC Machining Parts

Residual stresses from CNC machining would create part of the oxidation rate differences.
Surface roughness variations (Ra 0.8-1.2μm) affected dye absorption in a way.

What's Our Solution?

According to potential problems, we took the steps to handle them as below:

#Step 1: Redesigned the fixture.

Firstly, the production team developed custom titanium fixtures with rotating clips. And then we would ensure 8mm equal spacing between all 50 parts

#Step 2: Did A Process Optimization

As for the several parameters of the the anodizing process, we did a process optimization.

Step 3: Did A Pre-Treatment for 6061-T5 Aluminum Anodizing

We added stress-relief annealing post-CNC machining.
Through glass bead blasting, the surface of the aluminum parts has a standardized surface finish.

Parameter	Before	After
Temperature	20±5°C	18±0.5°C
Current Density	2.5 A/dm²	2.2 A/dm²
Agitation	Manual	Automated paddle (15 strokes/min)

Reslut & Feedback

Results: After taking these steps, we found that the final aluminum parts achieved consistent color. The anodizing layer thickness uniformity improved to ±1.5 μm. The aluminum parts look as our client expected.

After receiving the aluminum, the client confirmed it with us by sending an email:

“We have received all 50 pieces of aluminum parts. Color consistency matches our prototype exactly. Attaching approval for full production-1000 pieces with the same requirements.”

Conclusion

This case showed a common issue in the aluminum anodizing process. That’s unpredictable color variations that can undermine precision-machined components. As for our client, if there were inconsistent finishes, they risked delaying a product launch and damaging brand perception.

Why Choose Beska’s CNC Machining and Anodizing Services?

30+ kinds of surface finish with real-time monitoring (pH, temp, current)
100+ kinds of materials available; we would help you select the most proper material for your unique project
Free DFM analysis to prevent color variation risks in anodizing

We would support your CNC machining project. Contact us today for more details!

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