Understanding Dezincification in Copper Alloys
Dezincification is a selective corrosion process specific to copper-zinc alloys (brass) where zinc is preferentially leached from the alloy, leaving behind a porous, weak copper-rich residue. This form of corrosion can lead to sudden failures in brass components used in water systems, marine applications, and industrial processes – often without visible warning until catastrophic failure occurs.
At CoreMetal Steel, we supply brass and copper alloy products including dezincification-resistant (DZR) brass, and our technical team regularly advises on material selection to prevent corrosion-related failures.
The Dezincification Mechanism
How It Happens
Dezincification occurs through an electrochemical process:
- The brass surface is exposed to a corrosive environment (typically water with dissolved salts)
- Zinc atoms in the alloy are more electrochemically active than copper
- Zinc dissolves (corrodes) preferentially, entering the solution as Zn2+ ions
- Copper is redeposited in a porous, sponge-like structure
- The remaining copper matrix lacks structural integrity
Types of Dezincification
| Type | Appearance | Characteristics | Risk Level |
|---|---|---|---|
| Plug dezincification | Local isolated zones | Deep plugs of dezincified metal | Higher – sudden failure |
| Layer dezincification | Uniform layer across surface | Even removal of zinc across entire surface | Moderate – gradual weakening |
Plug dezincification is more dangerous because it causes localized penetration and sudden failure with little warning. Layer dezincification causes uniform wall thinning that may be detectable before failure.
Affected Alloys
High-Risk Brass Alloys
Alloys with higher zinc content and single-phase (alpha) structure are most susceptible:
| Alloy | Designation | Zn Content | Susceptibility |
|---|---|---|---|
| Cartridge Brass | C26000 (70/30) | 30% | Moderate |
| Yellow Brass | C26800 (65/35) | 35% | High |
| Naval Brass | C46400 | 39% | Moderate (Sn provides some resistance) |
| Muntz Metal | C46900 (60/40) | 40% | High |
| Free-Cutting Brass | C36000 | 35-37% | High |
Resistant Alloys
Alloys with specific additions or lower zinc content resist dezincification:
- Admiralty Brass (C44300): Contains tin and arsenic inhibitor
- DZR Brass (CZ132/CW602N): Contains arsenic, antimony, or phosphorus inhibitor (0.02-0.06%)
- Copper-Nickel (C70600/C71500): No zinc content, immune to dezincification
- Aluminum Bronze (C63000): Minimal zinc, resistant
- Silicon Bronze (C65500): Very low zinc, resistant
- Red Brass (C23000): 15% zinc, low susceptibility
Environmental Conditions That Promote Dezincification
- Water chemistry: Soft, acidic water (pH below 6.5) with low mineral content
- Temperature: Accelerated above 60C, significant above 80C
- Stagnant water: No flow allows corrosive species to concentrate
- High chloride content: Marine environments, coastal areas, salt-contaminated water
- High sulfate content: Industrial water, groundwater
- Low oxygen: Stagnant, anaerobic conditions promote plug attack
- High velocity: Can accelerate initial attack but may also inhibit by flushing
Testing Methods for Dezincification
ISO 6509: Corrosion by Dezincification
The international standard test method:
- Test solution: 0.01M potassium chloride + 0.5g/L copper(II) chloride
- Temperature: 75 plus/minus 1C
- Duration: 30 days
- Acceptance criterion: Maximum depth of dezincification less than or equal to 200 micrometers
- Evaluation: Cross-section examination under microscope
BS EN 12851 / BS 2874
British standards for DZR brass products:
- Similar test conditions to ISO 6509
- Specific requirements for plumbing fittings and forgings
- Maximum dezincification depth limits
ASTM B895
Standard test method for dezincification of copper-zinc alloys:
- Alternative test parameters available
- Applicable to all copper-zinc alloy forms
- Includes both 30-day and accelerated methods
Prevention Strategies
1. Material Selection
The most effective prevention is choosing the right alloy:
- DZR (Dezincification Resistant) brass: Contains 0.02-0.06% arsenic, antimony, or phosphorus
- Low-zinc alloys: Red brass (85Cu-15Zn), gunmetal (88Cu-10Sn-2Zn)
- Copper-nickel: For severe marine conditions
- Aluminum bronze: For high-strength, corrosion-resistant applications
2. Inhibitor Additions
Small additions of specific elements inhibit dezincification:
| Inhibitor Element | Optimal Addition | Mechanism |
|---|---|---|
| Arsenic (As) | 0.02-0.06% | Forms protective film on beta phase |
| Antimony (Sb) | 0.04-0.1% | Similar to arsenic, less toxic |
| Phosphorus (P) | 0.01-0.05% | Grain refinement + inhibition |
3. Water Treatment
- pH adjustment to neutral or slightly alkaline (pH 7-8.5)
- Corrosion inhibitors in closed-loop systems
- Reducing dissolved oxygen content
- Maintaining water velocity to prevent stagnation
4. Cathodic Protection
- For large brass components in marine environments
- Sacrificial anodes (zinc or aluminum) protect brass fittings
- Effective for sea water cooling systems
5. Protective Coatings
- Internal epoxy or cement linings for brass pipe fittings
- Prevents direct water-to-brass contact
- Effective for water distribution systems
Industry Applications and Requirements
| Industry | Standard | Requirement |
|---|---|---|
| Plumbing (UK) | BS EN 806, Water Regulations | DZR brass mandatory for all water fittings |
| Plumbing (Australia) | AS/NZS 3500, WaterMark | DZR brass for hot and cold water |
| Marine | Lloyds, DNV, ABS | CuNi or DZR for seawater systems |
| HVAC | EN 1254, EN 12449 | DZR brass for heat exchanger components |
Identifying Dezincification in Service
Visual Indicators
- Pink or copper-colored areas on brass surface (normally yellow/gold)
- Brittle, crumbly surface texture in affected areas
- Pinhole leaks in pipe fittings
- Reduced wall thickness without obvious external corrosion
- White deposits on external surface near leak points
Diagnostic Methods
- Cross-section microstructure examination
- Chemical analysis of the affected zone
- Hardness testing (dezincified zone is softer)
- Ultrasonic thickness measurement for wall loss
Conclusion
Dezincification is a serious but preventable form of corrosion in copper-zinc alloys. By understanding the mechanism, selecting appropriate alloys (especially DZR brass for water applications), and implementing proper environmental controls, engineers can eliminate dezincification-related failures.
CoreMetal Steel supplies DZR brass and all copper alloy products including pipe, tube, plate, bar, and fittings. Contact our team at tracy@coremetalsteel.com for material recommendations and corrosion-resistant alloy selection.