Gas Corrosion Resistance Testing for Automotive Components

Gas corrosion resistance testing evaluates how automotive parts, connectors, and electronic assemblies withstand trace corrosive pollutants such as hydrogen sulfide, sulfur dioxide, nitrogen dioxide, and chlorine under accelerated laboratory conditions. Conducted to internationally recognized standards such as IEC 60068-2-60, ISO 21207, ASTM B845, and GB/T 2423.51, mixed flowing gas (MFG) testing compresses years of field exposure into days or weeks. This article explains the test principle, applicable standards, sample types, evaluation criteria, and practical applications of gas corrosion testing for automotive components.

Technical Overview

Throughout their service life, automobiles operate in atmospheres containing low concentrations of chemically active gases. Typical pollutants include hydrogen sulfide (H2S), sulfur dioxide (SO2), nitrogen dioxide (NO2), chlorine (Cl2), and hydrogen chloride (HCl), which originate from vehicle exhaust, industrial emissions, fossil fuel combustion, wastewater treatment plants, livestock farming, landfills, tunnels, and volcanic or geothermal sources. Although these gases are often present at only parts-per-billion (ppb) concentrations, they react with sensitive metals such as silver, copper, tin, zinc, and nickel when combined with elevated relative humidity, forming resistive sulfide, oxide, and chloride corrosion films.

For automotive electronic systems, the consequences are well documented: silver contacts tarnish to silver sulfide (Ag2S), copper terminals develop insulating films, printed circuit boards suffer creep corrosion, and connector interfaces exhibit unstable or rising contact resistance. Because such degradation develops slowly in the field, laboratory gas corrosion testing is used to accelerate the mechanism by exposing samples to precisely controlled mixtures of corrosive gases, temperature, and humidity inside a mixed flowing gas (MFG) environmental chamber. The results allow engineers to compare plating systems, verify conformal coating coverage, and confirm that connectors, sensors, and control units will remain reliable throughout the vehicle design life.

• Corrosive species: H2S, SO2, NO2, Cl2, and HCl, tested individually or in combination at ppb to low-ppm concentrations
• Climatic conditions: typically 25 °C to 40 °C with 70 % to 75 % relative humidity, held constant throughout exposure
• Test durations: commonly 4, 7, 10, 14, or 21 days of continuous exposure, selected according to the severity level required
• Correlation objective: reproduce, in an accelerated manner, the corrosion damage expected from years of service in industrial, urban, tunnel, and agricultural atmospheres

Testing Samples

Gas corrosion testing is applicable to any automotive component whose metallic surfaces, contact interfaces, or protective finishes may be exposed to ambient air during service. The most frequently submitted sample categories are described below.

Electronic Assemblies and Control Units

Engine control units (ECUs), transmission controllers, body electronics modules, battery management systems (BMS), on-board chargers, and bare or fully assembled printed circuit boards (PCBs/PCAs) are tested to verify solderable finishes, connector platings, and the coverage and barrier performance of conformal coatings against gaseous pollutants.

Connectors, Terminals, and Contact Systems

Automotive connectors and terminal pairs are among the most tested items because contact interfaces are directly exposed to ambient air through unmated sections, vented housings, and mating cycles. Tin-plated, silver-plated, nickel-plated, and gold-flashed contact systems are typically evaluated in both mated and unmated configurations, with contact resistance measured before and after exposure.

Sensors, Relays, and Switches

Pressure sensors, position sensors, temperature sensors, oxygen and NOx sensors, relays, micro switches, and keypads contain precision contact and spring structures made of silver or copper alloys that are highly sensitive to sulfide tarnishing. Gas corrosion testing confirms that contact resistance and switching performance remain within specification after exposure.

Metallic Parts, Platings, and Coatings

Decorative trim, nameplates, emblems, fasteners, busbars, electromagnetic shielding cans, brackets, and coating test coupons are tested to assess tarnish resistance, pore-free plating quality, coating integrity, and substrate corrosion protection under polluted, humid atmospheres.

Testing Items

A complete gas corrosion test program combines controlled environmental exposure with electrical and physical characterization. Depending on the product specification, the following test items are typically included.

• Initial and final visual inspection with photographic documentation and corrosion grade rating of the affected surface area
• Contact resistance measurement of mated terminal and connector pairs at the milliohm level, before and after exposure
• Insulation resistance and dielectric withstand (hipot) verification after exposure
• Surface morphology and corrosion product analysis by scanning electron microscopy with energy-dispersive spectroscopy (SEM/EDS)
• Metallographic cross-section analysis to evaluate plating thickness, porosity, and corrosion penetration depth
• Functional and electrical performance verification of modules, relays, and sensors after exposure
• Mass change measurement of metallic coupons where specified by the test plan

Testing Methods

Testing is performed in purpose-built mixed flowing gas chambers equipped with precision mass flow controllers, gas dilution systems, and real-time analyzers that continuously monitor gas concentration, temperature, and humidity. Samples are preconditioned, characterized, and then exposed continuously for the specified duration. The principal methods and standards are summarized below.

IEC 60068-2-60 / GB/T 2423.51 — Test Ke (Mixed Flowing Gas)

This is the most widely applied method for automotive electronic components. The standard defines several severity methods that differ in gas combination and concentration. Method 1 exposes samples to approximately 100 ppb H2S combined with approximately 500 ppb SO2 at 25 °C and 75 % relative humidity. The multi-gas methods combine H2S, SO2, NO2, and Cl2 at concentrations on the order of 10 ppb to 200 ppb, typically at 25 °C to 30 °C and 70 % to 75 % relative humidity. Common durations include 4, 7, 10, 14, and 21 days. GB/T 2423.51 is the Chinese national standard technically equivalent to this method.

ISO 21207 and ISO 10062 — Polluting Gas Corrosion Tests

These standards specify accelerated corrosion tests in artificial atmospheres containing polluting gases such as H2S and SO2, at controlled temperature and humidity. ISO 21207 defines test methods of differing severity suitable for functional performance evaluation, while ISO 10062 covers very low gas concentration exposure for metallic and non-organic coatings and electronic applications.

ISO 6988 / GB/T 9789 — Sulfur Dioxide Test

For components that must resist sulfur-bearing industrial atmospheres, the sulfur dioxide (Kesternich-type) test exposes samples to a humid atmosphere containing SO2. It is frequently applied to metallic coatings, platings, and protective paint systems on chassis and fastener hardware.

ASTM B845 — Mixed Flowing Gas Test Guide

ASTM B845 defines classes of mixed flowing gas tests using various combinations of H2S, NO2, Cl2, and SO2 at ppb levels. It is widely used to evaluate the tarnish resistance of precious and non-precious metal finishes, and is supported by related practices for equipment and calibration.

Within the automotive industry, these test methods are commonly invoked as part of the broader environmental and electrical validation framework defined in the ISO 16750 series, as well as OEM-specific engineering specifications. Independent verification is typically carried out by accredited third-party laboratories using calibrated MFG chambers and traceable gas standards.

Applications

Gas corrosion resistance testing supports the entire automotive development cycle, from material selection and design validation to production quality control and field failure analysis. Typical applications include:

• Design validation of connectors, terminals, relays, and control modules for industrial, urban, tunnel, and high-humidity service environments
• Comparison and selection of plating systems, including tin, silver, nickel, zinc alloys, and gold-flash over nickel barriers
• Qualification of conformal coatings, potting compounds, and gasket designs for their barrier effect against gaseous pollutants
• Reliability evaluation of new energy vehicle (NEV) components, including battery busbars, BMS boards, and high-voltage interconnection hardware
• Supplier quality control, incoming inspection, and periodic production audit testing
• Root cause analysis of field returns by reproducing corrosion morphology observed in failed parts
• Export compliance and customer submission support, with test reports issued by accredited third-party laboratories

FAQ

What is gas corrosion resistance testing for automotive components?

It is an accelerated laboratory test in which automotive parts are exposed to controlled, very low concentrations of corrosive gases such as H2S, SO2, NO2, and Cl2, combined with elevated temperature and humidity. The test simulates years of exposure to polluted atmospheres and reveals tarnishing, film growth, and contact resistance degradation within days or weeks.

How does gas corrosion testing differ from salt spray testing?

Salt spray testing (for example, per ISO 9227, ASTM B117, or GB/T 10125) simulates chloride-rich marine or de-icing salt environments using a sodium chloride mist, and primarily drives electrolytic corrosion. Gas corrosion testing instead uses ppb-level pollutant gases that chemically attack silver, copper, and other sensitive metals, making it the appropriate method for electronic contacts, PCBs, and modules exposed to industrial and exhaust-gas atmospheres. The two methods are complementary and address different field failure mechanisms.

Which gases are used and at what concentrations?

The most common test atmospheres combine hydrogen sulfide, sulfur dioxide, nitrogen dioxide, and chlorine, with individual gas concentrations typically ranging from about 10 ppb up to several hundred ppb, or up to ppm levels for the single-gas SO2 test. The exact combination and severity are defined by the selected method in standards such as IEC 60068-2-60 or ASTM B845, or by the customer specification.

How long does a typical test take?

Exposure durations are selected according to the target severity level and typically range from 4 days (96 hours) to 21 days (504 hours), with 10-day and 14-day programs being common for automotive electronics. Additional time is required for preconditioning, initial and final electrical measurements, and any cross-section or microscopy work.

What sample quantity is required for testing?

Typical programs use three to ten pieces per condition so that samples can be allocated to electrical measurement, destructive cross-sectioning, and retained controls. Samples should represent production intent, including final plating and coating processes. Connector tests usually require complete mated pairs to allow contact resistance measurement before and after exposure.

How are test results evaluated and judged?

Evaluation normally combines visual corrosion grading of discolored surface area, measurement of contact resistance change on mated pairs, and microscopic or cross-sectional analysis of corrosion products. Pass or fail criteria are defined by the applicable product standard or customer specification, for example, a maximum allowable contact resistance increase or an allowable percentage of corroded surface area.