ASTM G85: THE FAMILY OF MODIFIED SALT SPRAY TESTS

Real corrosion isn’t constant. Real environments aren’t gentle.

ASTM G85 is a modification of the well-known ASTM B117 salt spray method. First approved in 1985, instead of a single continuous fog condition, G85 introduces five different annexes (A1–A5) — each engineered to replicate chemical, thermal, and environmental stresses that reflect real-world corrosion far more closely than continuous fog alone.

This practice applies to ferrous and nonferrous metals, organic coatings, inorganic coatings, and plated systems. Where B117 is a constant environment, G85 is cyclic, chemical, and aggressive.

G85 Annex Overview

• A1 – Acetic Acid Salt Spray (AASS): Uses a 5% NaCl solution acidified with glacial acetic acid to reach pH 3.1–3.3. Exposure is at 35 ± 2°C. Often run 144–240 hours for evaluation of decorative chrome plating on zinc and steel.
• A2 – Cyclic Acidified Salt Spray: Similar chemistry to A1 but more acidic (pH 2.8–3.0). The test alternates between fog and purge cycles. A wet bottom is typically maintained to avoid drying, though dry-bottom variants exist for specific alloys (e.g., 2000 series Al) and coatings.
• A3 – Acidified Synthetic Seawater (SWAAT): Replaces NaCl with synthetic ocean salt, adjusted to pH 2.8–3.0. Used extensively for exfoliation-resistant aluminum alloys (recommended 49°C) and for organic coatings (24–35°C). Cycles alternate 30 minutes of spray and 90 minutes of 98% RH soak.
• A4 – SO₂ Salt Spray Exposure: Introduces sulfur dioxide gas into the chamber atmosphere. Solutions may be 5% NaCl or 5% synthetic sea salt. Exhibits two climate cycles that combine salt/sea water fog with periodic SO₂ dosing, simulating acid rain and industrial atmospheric pollution.
• A5 – Dilute Electrolyte Wet/Dry Cycling: Uses a low-concentration electrolyte (0.05% NaCl + 0.35% ammonium sulfate, pH 5.0–5.4) and alternates 1 hour fog at ambient conditions with 1 hour dry-off at ~35°C using fresh-air purge. Ideal for understanding corrosive effects of wet/dry cycles that collapse coatings and expose substrate weaknesses.

G85 recreates the same volatile conditions that drive real-world corrosion — dry-outs, crystallization, acidified atmospheres, SO₂ pollutants, synthetic seawater chemistry, and rapid transitions in humidity and temperature.