1 Research Methods

1.1 Design Framework

The evaluation follows a controlled comparative design. All test parts were CNC-machined from 6061-T6 aluminum and 304 stainless steel using identical cutting parameters to maintain consistent baseline roughness. Each part was subsequently processed through one finishing technique under fixed conditions aligned with industrial standards (MIL-A-8625 for anodizing, ASTM A380 for passivation).

1.2 Data Sources

Data were collected from three measurement categories:

• Surface roughness (Ra) measured with a contact profilometer.

• Oxide-layer thickness measured through eddy-current coating testing.

• Corrosion resistance evaluated in a neutral salt-spray chamber with 5% NaCl.

All raw data sets, calibration logs, and environmental parameters are included in the appendix to ensure full reproducibility.

1.3 Experimental Tools and Models

The experimental workflow used:

• 3-axis CNC milling center for sample production

• Bead-blast chamber with 120-mesh media

• Type II sulfuric-acid anodizing line

• Stainless-steel passivation bath formulated with nitric-free citric chemistry

• Belt-polishing machine with sequential 800- to 2000-grit abrasives

Calibration of all measuring instruments followed manufacturer recommendations, and each sample underwent three repeated measurements to reduce random error.

2 Results and Analysis

2.1 Surface Roughness Comparison

Table 1 presents Ra values after each finishing process. Sandblasting produced the most consistent matte surface (Ra 1.2–1.4 μm). Mechanical polishing achieved the lowest Ra (0.05–0.08 μm), suitable for reflective parts. Anodizing maintained moderate roughness but significantly improved oxide-layer uniformity.

2.2 Corrosion-Resistance Performance

Salt-spray exposure showed that anodized samples maintained structural and color stability for over 500 hours without pitting. Passivated stainless-steel samples exhibited improved passive-film integrity, reducing spot corrosion by 68% compared with untreated controls.

2.3 Visual and Aesthetic Stability

Color-shift measurements under 500-lux illumination demonstrated that anodized surfaces maintained the most stable hue. Sandblasted surfaces displayed minimal glare due to diffuse reflection properties, supporting their application in consumer electronics housings.

2.4 Comparison with Existing Research

The measured performance aligns with earlier findings describing anodized aluminum’s high corrosion tolerance and sandblasting’s stable topography (Refs. 2, 3). The data additionally show quantifiable improvements in passivation outcomes using citric-acid formulations, expanding on previous nitric-based studies.

3 Discussion

3.1 Interpretation of Results

Differences in performance stem from each process’s underlying material interactions. Anodizing forms a structured porous oxide layer that resists chemical attack. Sandblasting modifies the micro-topography through uniform abrasion. Passivation strengthens the chromium-rich passive film on stainless steel, reducing its reactivity. Mechanical polishing physically reduces asperities through progressive abrasive steps.

3.2 Limitations

The evaluation focuses on two metal materials and specific process parameters. Variations in alloy composition, media size, acid concentration, or polishing sequence may alter outcomes. Additional long-term fatigue data would provide further insight.

3.3 Practical Implications

Manufacturers may use these results to match finishing methods with functional requirements. Components exposed to marine environments benefit from anodizing; consumer-facing enclosures may favor sandblasting; precision medical parts typically require passivation; and optical components rely on ultra-low-roughness polishing.

4 Conclusion

The comparison demonstrates distinct performance profiles across four CNC-machining finishing methods. Anodizing offers superior corrosion resistance, sandblasting provides consistent matte textures, passivation enhances stainless-steel chemical stability, and mechanical polishing delivers the lowest roughness levels. These findings support targeted selection of finishes based on structural, visual, or environmental demands and indicate further study potential in multi-step hybrid finishing.