Determining the right surface finish for aluminum components requires evaluating corrosion needs, dimensional constraints, and cost against your specific application requirements. With decades of experience anodizing parts for aerospace, audio, and medical sectors, the Type II decision often comes down to understanding key performance trade-offs versus alternatives.
Type II anodizing works best for indoor applications requiring moderate corrosion protection with minimal dimensional change. It adds 0.0002-0.0007 inches thickness while maintaining tighter tolerances than Type III anodizing or powder coating.
Learn to assess dimensional impact, prep needs, and cost to see if Type II anodizing fits your tolerance, durability, and budget requirements.
Table of Contents
What Does Type II Anodizing Cost Per Square Foot?
Type II anodizing typically costs $0.50-$2.00 per square foot for standard colors, with minimum charges of $65-$150 per batch making it economical above 25-50 parts. For smaller quantities, expect to pay the minimum charge regardless of part count, while production volumes bring per-part costs down significantly.
From our experience processing hundreds of aluminum components, batch minimums create the biggest cost impact. A single part might cost $125 due to minimum charges, but 100 parts in the same batch could cost just $2-3 each. Complex geometries requiring masking or special racking can increase costs 25-50% due to additional setup time.
Quick Decision Tool:
- 1-5 parts: Expect $60-125 each due to minimum charges
- 25-100 parts: Budget $3-8 per part with setup costs absorbed
- 200+ parts: Expect $0.50-3.00 per part for standard colors
The biggest cost surprise is often custom colors, which can add 25-40% to base pricing and require approval samples. Standard colors like clear and black are most economical, while custom colors require specialized dye processes. Setup fees apply per batch regardless of part count, so consolidating multiple part numbers into single runs provides significant savings.
Design Takeaway: Calculate your break-even around 25-50 parts minimum. Group prototype parts into single anodizing batches and specify standard colors (clear, black) until production volumes justify custom color development costs.
Type II vs Type III Anodizing: Which Is More Durable?
Type III hard anodizing provides significantly superior durability with surface hardness of 60-70 Rockwell C compared to Type II’s minimal hardness impact. Choose Type III for high-wear applications and Type II for corrosion protection and aesthetics.
From our experience anodizing thousands of components across aerospace and industrial applications, the durability difference is substantial. Type III achieves 60-70 Rockwell C hardness (comparable to case-hardened steel) while untreated aluminum measures only 15 Rockwell C. Type II is so thin that hardness isn’t a main attribute and doesn’t show up “hard” unless special micro techniques are used Types of Anodizing.
When to Choose Each Type:
| Application | Type II | Type III | Decision Factor |
|---|---|---|---|
| Audio faceplates | ✓ | ❌ | Cost-effective appearance |
| Sliding mechanisms | ❌ | ✓ | Prevents galling/wear |
| Medical housings | ✓ | ✓ | Depends on sterilization needs |
| Outdoor brackets | ❌ | ✓ | Environmental resistance |
| Consumer electronics | ✓ | ❌ | Aesthetics over durability |
Type III demonstrates wear resistance up to 100 times better than untreated aluminum and exceeds 336 hours in 5% salt spray testing. However, Type III coatings are brittle, so sharp edges and pointed surfaces have limited wear resistance due to coating build-up perpendicular to the substrate.
Design Takeaway: Use Type II for indoor applications prioritizing cost and appearance. Specify Type III only when wear resistance, sliding contact, or harsh environments justify the 2-3x cost premium and dimensional impact.
How Much Thickness Does Type II Anodizing Add?
Type II anodizing adds 0.0002-0.0006 inches (5-15 microns) total thickness, with approximately half penetrating into the aluminum and half building outward from the original surface.
Type II sulfuric acid anodizing results in thickness of 0.0002-0.0006 inches for decorative applications. You can typically expect 50% buildup and 50% penetration when anodize is built up. This means a 0.0004″ coating adds 0.0002″ to external dimensions while reducing hole diameters by 0.0002″.
Real Dimensional Impact Examples:
- 0.250″ clearance hole → becomes 0.2496″ after 0.0004″ anodizing
- M6 x 1.0 tapped hole → requires pre-tap 0.0002″ oversize
- 6.000″ external dimension → measures 6.0002″ after anodizing
- Press-fit shaft (0.001″ interference) → reduce machined diameter by anodizing thickness
For Type II, coatings range from 0.0003-0.0005″ penetration and 0.0003-0.0005″ buildup. Thicker coatings are needed for saturated black colors to absorb sufficient dye. Most clear anodizing uses the thinner end of the range.
Drawing Specification Guidelines:
- Specify “MIL-A-8625 TYPE II, 0.0004″ THICK TYP”
- Note “DIMENSIONS BEFORE ANODIZING” on critical features
- Call out masking for precision surfaces requiring unchanged dimensions
- Plan hole sizes 0.0002-0.0003″ larger to compensate
Design Takeaway: For assemblies with tolerances tighter than ±0.001″, coordinate anodizing thickness with machining dimensions early in design. Most standard applications accommodate the minimal thickness without design changes.
Is Type II Anodizing Suitable for High-Wear Applications?
No, Type II anodizing is not suitable for high-wear applications. MIL-PRF-8625F specifies no wear index requirements for Type II, while Type III requires maximum 1.5-3.5mg/1000 cycles on Taber abrasion testing, indicating Type II lacks measurable wear resistance.
From our experience finishing components across demanding applications, Type II has no specified wear index in the standard, nor corresponding surface hardness measurements. Type II is restricted to parts that don’t experience stress or have recesses, particularly on airplanes. The porous nature of Type II coating leaves it susceptible to abrasion damage, and organic contaminants like oils can infiltrate the pores.
Wear Performance Comparison:
| Application Type | Type II Performance | Better Alternatives | Cost Comparison |
|---|---|---|---|
| Sliding rails/guides | Fails quickly | Type III | 2–3× more expensive |
| Threaded fasteners | Thread seizing | Type III + PTFE seal | 3–4× more expensive |
| Gear surfaces | Rapid wear-through | Hardcoat + coating | 4–5× more expensive |
| Handle/grip areas | Adequate | Type II acceptable | Base cost ($2–6/sq ft) |
Real Wear Data: Type III hard coatings require maximum wear index of 1.5mg/1000 cycles for most alloys (3.5mg for high-copper alloys) when tested per MIL-PRF-8625F. Type II has no comparable specification, indicating it cannot meet measurable wear standards.
Practical Alternatives:
- Light wear: Keep Type II, plan for replacement cycles
- Moderate wear: Type III hard anodizing (2-3x cost, 10-100x wear life)
- Heavy wear: Type III + PTFE seal or alternative coatings
- Budget constraints: Consider bare aluminum with regular replacement
Design Takeaway: Reserve Type II for corrosion protection and aesthetics only. For any sliding contact, repeated assembly, or mechanical stress, budget for Type III or plan component replacement cycles. The 2-3x cost increase for Type III typically pays for itself through extended service life.
Can Different Aluminum Alloys Be Anodized Together?
Yes, different aluminum alloys can be anodized in the same batch, but expect significant color variations and potentially inconsistent coating quality. Budget 10-25% extra for mixed-alloy processing and plan separate batches for cosmetic assemblies requiring color matching.
From our experience processing mixed-alloy components, chromic acid anodizing is insensitive to alloy differences, while sulfuric acid anodizing might coat too much in some areas and not enough in others. 5052 and 6061 tend to look matte black after anodizing, while 7075, 2000 series, and 3000 series usually look more gray.
Mixed-Alloy Outcomes:
| Alloy Combination | Color Consistency | Coating Quality | Recommendation |
|---|---|---|---|
| 6061 + 6063 | Good match | Uniform thickness | Acceptable for batching |
| 6061 + 5052 | Slight variation | Good quality | Acceptable |
| 6061 + 7075 | 15–25% color difference | Variable thickness | Separate if cosmetic |
| Any + 2024 | Significant mismatch | Poor, requires pre-treatment | Avoid mixing |
Cost Impact Analysis: Different alloys anodize differently, affecting the quality and cost of the finish. Mixed-alloy batches often require process adjustments, extended cycle times, or additional quality control, adding 10-25% to standard anodizing costs. Certain alloys like 6061 and 6063 stand out for their ability to produce consistent finishes while minimizing additional processing costs.
Quality Control Strategies:
- Sample first: Test mixed-alloy samples before committing to production
- Group similar alloys: Batch 6000 series together, separate 2000/7000 series
- Specify acceptance criteria: Define allowable color variation ranges
- Plan separate runs: Budget separate batching for critical aesthetic parts
Specification Guidelines:
- Note “MIXED ALLOY BATCH ACCEPTABLE” on non-cosmetic parts
- Specify “IDENTICAL ALLOY REQUIRED” for color-critical assemblies
- Include color variation acceptance criteria in drawings
Design Takeaway: Mixed-alloy batching works for functional applications where slight color variations are acceptable and can save 15-30% versus separate batching. For cosmetic assemblies, specify identical alloys or budget for separate anodizing runs to ensure color consistency.
What Drawing Notes Are Required for Type II Anodizing?
Specify “MIL-A-8625 TYPE II, CLASS [1 or 2], [COLOR], 0.0004″ THICK TYP” as the minimum callout. Include masking requirements, dimensional notes, and surface preparation specifications to prevent costly rework and ensure proper results.
From our experience reviewing hundreds of anodizing drawings, incomplete specifications cause 60-80% of quality issues and delays. The specification states that anodic coating thickness should be specifically called out by the purchase documents and/or the part drawing. Class 1 means clear/undyed coating, while Class 2 indicates dyed coatings.
Critical Drawing Callouts:
- Basic specification: “MIL-A-8625 TYPE II, CLASS 2 BLACK, 0.0004″ ±0.0001″ THICK”
- Masking requirements: “MASK: THREADS (2) M6x1.0, BORE Ø6.000 ±0.001”
- Dimensional reference: “DIMENSIONS SHOWN BEFORE ANODIZING”
- Surface preparation: “63 Ra MAX BEFORE ANODIZING”
- Special requirements: “HOT WATER SEAL” or “DICHROMATE SEAL” if needed
Vendor Communication Strategy: Always provide clear anodizing specifications in purchase orders and include reference standards. For certification compliance, many anodizers require additional testing like salt spray and coating weight verification, adding $1,500+ to costs. Communicate acceptance criteria upfront and request process certifications for critical applications.
Quality Verification Methods: Anodizing thickness can be measured non-destructively using eddy current coating thickness gages, with PosiTector 6000 NAS probes specifically designed for anodizing measurement. Quality control includes visual checks for color variations, coating weight testing, seal quality verification, and thickness measurement with records kept for 5+ years.
Design Takeaway: Include complete anodizing specifications on drawings with clear masking callouts and dimensional references. Request samples for color approval and establish inspection criteria before production. Budget for additional testing costs when MIL-A-8625 compliance certification is required.
What's the Typical Lead Time Impact of Adding Type II Anodizing to My Project?
Type II anodizing typically adds 3-7 business days to project timelines, with rush processing available in 1-2 days at 50-75% premium pricing. Plan accordingly as anodizing cannot begin until all machining is complete.
Standard production on anodizing orders is 7-10 days with 1-3 day shipping. From our experience coordinating hundreds of anodized components, lead times vary significantly based on vendor size and location. Third-party anodizing suppliers located off-site from manufacturing facilities add additional lead time beyond typical 2-3 day machining turnaround, plus minimum lot charges.
Lead Time Variables by Vendor Type:
- Small shops (1-3 employees): 7-14 days, less predictable scheduling
- Medium facilities (5-15 employees): 5-7 days, more consistent availability
- Large operations (20+ employees): 3-5 days, priority scheduling for volume orders
- Rush processing: 1-2 days available at 50-75% premium, quality may suffer
Volume Impact on Scheduling: Computer-automated systems control and monitor products through the entire anodizing process, with rack tags tracking job specifications and timing. Larger batches get priority scheduling since they justify longer tank runs. Orders under 25 parts often wait for batch consolidation, while 100+ piece orders typically process immediately.
Seasonal and Regional Factors: Busy periods occur during fall/winter months when outdoor construction slows and shops focus on batch processing. Summer months typically offer shorter lead times due to higher capacity utilization. Geographic location affects shipping time and vendor availability – coastal areas generally have more anodizing capacity than inland regions.
Backup Planning Strategies: Qualify 2-3 anodizing vendors to prevent single-source delays. Consider local powder coating as a fallback finish option. Build buffer time into project schedules, especially for first-time vendors or custom color requirements that may need multiple approval cycles.
Design Takeaway: Plan 7-10 days minimum for anodizing including processing and shipping. Start vendor qualification early and maintain backup options. Consider geographic proximity when selecting anodizers to minimize shipping delays and enable faster problem resolution.
How Does Type II Anodizing Compare to Type III or Powder Coating for Durability?
Type II provides adequate durability for indoor applications but significantly underperforms Type III and powder coating in wear resistance and environmental protection. Choose Type II for cost-effective corrosion resistance, Type III for wear applications, and powder coating for maximum weather resistance.
From our experience finishing components across diverse environments, durability requirements drive finish selection more than initial cost. Type III anodizing demonstrates wear resistance up to 100 times better than untreated aluminum and exceeds 336 hours in 5% salt spray testing . Type II may not be ideal for applications demanding high corrosion or abrasion resistance due to its porous nature.
Durability Comparison Matrix:
| Performance Factor | Type II Anodizing | Type III Anodizing | Powder Coating |
|---|---|---|---|
| Abrasion Resistance | Limited | Excellent (100× base aluminum) | Good |
| Salt Spray Resistance | 168–336 hours | 500+ hours | 1000+ hours |
| UV Resistance | Fair (may fade) | Good | Excellent |
| Chemical Resistance | Moderate | Good | Excellent |
| Impact Resistance | Poor (brittle) | Poor (brittle) | Excellent |
| Cost per sq ft | $0.50–2.00 | $2.00–5.00 | $3.00–6.00 |
Specific Failure Mode Analysis: Type II anodizing fails by wearing thin and showing aluminum substrate underneath, particularly at contact points and edges. Type III typically cracks at high-stress points but maintains thickness and protection. Powder coating may chip on sharp impacts but resists environmental degradation and provides excellent flexibility.
Testing and Validation Methods: MIL-PRF-8625F specifies Taber abrasion testing for Type III with maximum wear index of 1.5-3.5mg/1000 cycles, while Type II has no specified wear requirements. Durability testing includes coating thickness measurement, seal quality evaluation, and electrical conductivity testing for heat damage detection.
Long-Term Economic Analysis: While Type II offers the lowest initial cost at $0.50-2.00 per square foot, replacement cycles may make Type III or powder coating more economical over 5-10 years. Type III’s 2-3x cost premium often provides 10-50x service life improvement in demanding applications, making it cost-effective for high-wear scenarios.
Design Takeaway: Match finish selection to actual service conditions rather than minimizing initial cost. Type II works well for protected indoor environments where aesthetics and basic corrosion protection matter most. Invest in Type III for wear applications or powder coating for harsh environmental exposure to avoid premature replacement costs.
Conclusion
Type II anodizing provides cost-effective corrosion protection for indoor applications, while demanding environments require Type III or powder coating. Proper specifications, realistic lead time planning, and matching finish to service conditions prevent costly redesigns and delays.
Contact us to explore manufacturing solutions tailored to your aluminum anodizing requirements.
Frequently Asked Questions
Yes, but expect color variations at weld zones due to heat-affected microstructure changes. Plan welding before anodizing when possible, or specify separate anodizing runs for each welded assembly to ensure color consistency across the final product.
Specify “MASK THREADS” on drawings for critical fasteners, or tap holes 0.0002-0.0003″ oversize before anodizing. Standard hardware threads typically accommodate Type II thickness without modification. Test-fit fasteners before production if tolerance is critical.
Type II provides 168-336 hours salt spray resistance, adequate for covered outdoor use but not direct weather exposure. For full outdoor applications, upgrade to Type III (500+ hours) or powder coating (1000+ hours) to prevent premature degradation.
Type II adds 0.0002-0.0006″ total thickness, so features with tolerances tighter than ±0.001″ need dimensional compensation or masking. Plan hole sizes 0.0002-0.0003″ larger before anodizing. Critical fits may require post-anodizing assembly verification.
At 50 parts, expect $4-8 per part including setup allocation. At 200+ parts, costs drop to $2-4 per part as setup fees spread across more pieces. The break-even point typically occurs around 75-100 parts for most geometries.
Use eddy current thickness gauges like PosiTector 6000 NAS for non-destructive measurement. Reputable anodizers provide inspection certificates with thickness data. Request test coupons processed with your parts for independent verification if critical.
