Cold-Sprayed Copper Parts Salt Spray Corrosion Testing: Standards, Methods and Evaluation

Cold-sprayed copper parts salt spray corrosion testing is an accelerated laboratory procedure used to evaluate the corrosion resistance of copper components and coatings produced by cold gas dynamic spraying. By exposing cold-sprayed copper samples to a controlled sodium chloride fog in accordance with ISO 9227, ASTM B117 and GB/T 10125, manufacturers can verify surface durability, coating integrity and long-term reliability before products enter corrosive service environments. This article explains the test principle, sample preparation, applicable standards, evaluation methods and typical industrial applications.

Technical Overview

Cold spray, also known as cold gas dynamic spraying (CGDS) or kinetic spraying, is a solid-state deposition process in which fine copper powder particles are accelerated to supersonic velocities by a heated high-pressure gas stream, typically nitrogen or helium. Upon impact on a substrate, the particles undergo severe plastic deformation and bond metallurgically without significant melting. The result is a dense copper deposit with low oxidation, high electrical conductivity and near-bulk thermal properties, suitable for both coating applications and free-standing additive manufactured parts.

Although copper exhibits good corrosion resistance in many atmospheres, it is susceptible to degradation in chloride-containing environments, where pitting, tarnishing, and the formation of green copper chloride corrosion products can compromise appearance, dimensional accuracy, electrical contact resistance and coating adhesion. Cold-sprayed copper deposits may additionally contain residual porosity, inter-particle boundaries and work-hardened microstructures that can influence corrosion initiation and propagation compared with wrought copper.

Salt spray (salt fog) corrosion testing provides a standardized, accelerated method to assess the corrosion behavior of cold-sprayed copper parts under simulated marine and industrial atmospheres. The test exposes specimens to a continuous fine mist of neutral or acidified sodium chloride solution inside a controlled chamber. Widely applied specifications include ISO 9227, ASTM B117, ASTM B368 and the Chinese national standard GB/T 10125, all of which define chamber conditions, solution chemistry, collection rates and evaluation criteria.

Testing Samples

Cold-Sprayed Copper Coatings on Metallic Substrates

These specimens consist of a cold-sprayed copper layer deposited onto substrates such as aluminum alloys, steel, stainless steel or copper alloys. Typical sample formats include flat coupons (for example 100 mm × 50 mm), component sections, or complete production parts. Testing focuses on the corrosion resistance of the copper deposit, the copper–substrate interface and any galvanic interaction at exposed edges or coating defects.

Free-Standing Cold-Sprayed Copper Parts

Free-standing specimens are additively manufactured or spray-formed copper components produced entirely by cold spray, such as busbars, heat sink bodies, waveguide sections and conductive inserts. Testing evaluates the bulk corrosion response of the deposited material, including the effect of residual porosity and inter-splat boundaries on pitting and product formation.

Cold-Sprayed Copper Repairs and Rebuilt Components

Restored or dimensionally rebuilt copper and copper alloy components, in which cold-sprayed copper is used to fill machined defects or worn regions, are tested to confirm that repaired zones corrode no faster than the surrounding base metal and that the repair interface remains sound after chloride exposure.

Sample Preparation Requirements

• Samples should be cleaned with appropriate solvents to remove oils, fingerprints, machining residues and loose powder; abrasive cleaning is generally avoided unless representative of production finishing.
• Edges, cut surfaces and identification markings that are not part of the evaluated surface are protected with chemically inert masking tape or wax compliant with the referenced standard.
• A minimum of three identical specimens per condition is recommended to ensure statistical validity of the corrosion rating.
• Baseline documentation, including photographs, thickness measurements, surface roughness and porosity records, is collected before exposure.

Testing Items

Salt spray corrosion testing of cold-sprayed copper parts typically covers the following items, selected according to product specification and end-use environment:

• Neutral Salt Spray (NSS) test – the baseline chloride exposure for general corrosion assessment.
• Acetic Acid Salt Spray (AASS) test – an acidified fog used to accelerate corrosion of decorative and functional copper surfaces.
• Copper-Accelerated Acetic Acid Salt Spray (CASS) test – a severely accelerated test per ASTM B368, principally used for decorative copper and copper-nickel-chromium coating systems.
• Corrosion appearance evaluation – documentation of tarnish films, pitting, verdigris (green copper corrosion products), blistering and edge attack after defined exposure intervals.
• Corrosion rating and classification – quantification of the percentage of surface affected by corrosion, expressed as rating numbers in accordance with ISO 10289 or equivalent acceptance criteria.
• Post-exposure adhesion verification – pull-off or bend testing after salt spray exposure to confirm that corrosion has not degraded the cold-sprayed deposit–substrate bond.
• Mass loss and thickness loss measurement – gravimetric or metrological determination of material removal after removal of corrosion products.
• Functional property verification – measurement of electrical conductivity or contact resistance after exposure for electrically functional copper deposits.

Testing Methods

Neutral Salt Spray (NSS) – ISO 9227 / ASTM B117 / GB/T 10125

The test solution is prepared by dissolving sodium chloride in distilled or deionized water at a concentration of 50 ± 5 g/L. The solution pH is maintained at 6.5 to 7.2 at 25 °C. The chamber temperature is controlled at 35 °C ± 2 °C, and the fog collection rate must be 1 to 2 mL per hour per 80 cm² of horizontal collection area. Specimens are positioned at 15° to 30° from vertical, with evaluated surfaces facing upward and not shielded by other samples. Common exposure durations for cold-sprayed copper parts include 24 h, 48 h, 96 h, 168 h, 240 h, 500 h and 1000 h, as specified by the product standard or customer agreement.

Acetic Acid Salt Spray (AASS)

The AASS variant uses the same sodium chloride concentration, with glacial acetic acid added to adjust the collected solution pH to 3.1 to 3.3. The chamber operates at 35 °C ± 2 °C. This moderately accelerated environment is used to evaluate decorative copper finishes and to reveal inter-particle boundary attack more rapidly than the neutral test.

CASS Test – ASTM B368

The CASS solution additionally contains copper(II) chloride dihydrate (0.26 g/L), with pH adjusted to 3.1 to 3.3 and the chamber held at 49 °C ± 2 °C. This severe exposure is reserved for decorative copper-containing coating systems where rapid qualification is required.

Post-Exposure Evaluation Procedure

• After exposure, specimens are gently rinsed in clean running water no warmer than 40 °C to remove salt residue and dried with filtered compressed air, without aggressive mechanical action.
• Corrosion products may be chemically removed using standardized cleaning solutions so that mass loss and pitting can be accurately determined.
• The corroded area fraction is assessed visually or with image analysis, converted to a rating number per ISO 10289 (rating 10 for no corrosion down to rating 0 for more than 75 % affected area).
• Corrosion at cut edges, drill holes and deliberate scribe marks is reported separately, as these are excluded from or specially classified in most acceptance criteria.
• Results are reported with exposure duration, solution verification data, temperature records, collection rate and photographs before and after exposure.

Typical Acceptance Considerations

Because no universal pass–fail limit exists for cold-sprayed copper, acceptance criteria are defined by the applicable product standard or engineering specification. Common requirements include no red rust or exfoliation originating from the substrate, no blistering or delamination of the copper deposit, corrosion rating of at least 8 per ISO 10289 after the specified duration, and retention of minimum electrical conductivity for functional parts.

Applications

Salt spray corrosion testing of cold-sprayed copper parts supports quality control and qualification across multiple industries:

• Electrical and electronics manufacturing – busbars, connectors, conductive traces and shielding deposits where corrosion must not increase contact resistance.
• Thermal management – cold-sprayed copper heat sinks, cold plates and spreaders used in power electronics and server cooling systems.
• Marine and coastal equipment – conductive and structural copper deposits exposed to chloride-laden atmospheres, including shipboard electronics housings and antenna components.
• Component repair and remanufacturing – qualification of cold-sprayed copper rebuilds on valve seats, bearing surfaces and electrical contactors.
• Additive manufacturing – acceptance testing of cold-spray-printed copper parts intended for corrosive service environments.
• Railway and infrastructure – copper deposition used for earthing, lightning protection and current-carrying hardware exposed to outdoor atmospheres.
• Research and development – comparative studies of powder purity, gas type, process parameters and post-treatment (for example heat treatment or laser polishing) on the corrosion performance of cold-sprayed copper.

FAQ

What is cold-sprayed copper and how does it differ from other copper coatings?

Cold-sprayed copper is produced by accelerating copper powder to supersonic speed in a compressed gas stream so that particles plastically deform and bond on impact, entirely in the solid state. Unlike electroplating, hot-dip coating or thermal spray with flame or plasma, the material never melts, so the deposit retains very low oxide content, high purity and high electrical and thermal conductivity close to wrought copper.

Which standards govern salt spray testing of cold-sprayed copper parts?

The primary standards are ISO 9227 and GB/T 10125 for neutral, acetic acid and CASS salt spray exposures, ASTM B117 for neutral salt fog practice, ASTM B368 for the CASS test, and ISO 10289 (together with ASTM D1654 where applicable) for rating corroded specimens. Selection depends on the product specification and target service environment.

How long should a cold-sprayed copper part be exposed?

Exposure duration is set by the product or purchaser specification. Typical qualification programs use 96 h or 168 h for general industrial service, and extend to 500 h or 1000 h for marine or long-life applications. Intermediate inspections at 24 h or 48 h intervals help track corrosion progression.

How are corrosion test results interpreted for copper?

Copper does not exhibit red rust like ferrous metals; instead, corrosion appears as surface tarnish, darkening, pitting and green copper chloride or carbonate products. Evaluation therefore focuses on the affected surface area percentage, pit density and depth, adhesion of corrosion products, and any loss of deposit integrity, reported as rating numbers per ISO 10289.

Can salt spray results predict the service life of cold-sprayed copper parts?

No. Salt spray testing is a comparative, quality-control tool rather than a predictor of long-term outdoor performance, because the continuous chloride fog does not reproduce wet–dry cycling, ultraviolet exposure or pollutant chemistry found in real environments. It is used to compare materials, processes and protective measures against defined acceptance criteria; performance prediction should rely on natural exposure programs such as ISO 8565 or ISO 9223/9224 classification methods.

Where can cold-sprayed copper parts be tested?

Testing can be performed by accredited third-party laboratories or by in-house corrosion laboratories equipped with salt spray chambers compliant with ISO 9227 or ASTM B117, operating under recognized quality management systems with calibrated temperature, pH and collection-rate instrumentation.