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IS 1868:1997 is the Indian Standard (BIS) for anodic coatings on aluminium and its alloys - specification. This standard covers the requirements for anodic coatings on aluminium and its alloys. It classifies coatings into different grades based on minimum local thickness and specifies criteria for sealing, appearance, and corrosion resistance to ensure durability in architectural and industrial applications.
Lays down requirements for anodic oxidation coatings on aluminium and aluminium alloys, specifying properties and test methods.
Overview
Status
Current
Usage level
Frequently Used
Domain
Materials Science — Aluminium and Non-Ferrous Metals
! Always specify the correct coating grade based on environmental exposure; coastal or heavily industrialized areas require AC 25.
! Poor sealing is a primary cause of fading or staining in anodized aluminium. Insist on sealing quality tests like the dye spot test or admittance measurement.
! Ensure the base aluminium alloy is anodizing-quality, as metallurgical impurities can lead to visible surface defects after the coating process.
Anodizing of aluminium and its alloys — General specifications for anodic oxidation coatings on aluminium
Specifies general requirements and test methods for anodic oxidation coatings on aluminium for all purposes.
MIL-PRF-8625GU.S. Department of Defense (US)
HighCurrent
Anodic Coatings for Aluminum and Aluminum Alloys
Defines requirements for three types of anodic coatings, with a strong focus on corrosion resistance and wear for military/aerospace use.
ASTM B580-23ASTM International (US)
HighCurrent
Standard Specification for Anodic Oxide Coatings on Aluminum
Covers requirements for electrolytically formed anodic oxide coatings on aluminum, primarily for protective and decorative applications.
BS 3987:1991BSI (UK)
MediumWithdrawn
Specification for anodic oxide coatings on wrought aluminium for external architectural applications
Provided specifications for architectural anodizing in the UK, with a focus on durability and weather resistance.
Key Differences
≠IS 1868 primarily classifies coatings by thickness (Grades AC 5 to AC 25), similar to ISO 7599. In contrast, MIL-PRF-8625 classifies by process type: Type I (chromic acid), Type II (sulfuric acid), and Type III (hardcoat), which has different performance implications.
≠MIL-PRF-8625 mandates a stringent 336-hour salt spray corrosion test (ASTM B117) for its Type I and II coatings. IS 1868 references corrosion testing but does not mandate a specific duration for all grades, leaving it to agreement between parties.
≠IS 1868 includes hard anodic coatings (Grades HA, EHA) within the main standard, while the ISO framework often addresses hard anodizing in a separate standard, ISO 10074.
≠ISO 7599 and ASTM B580 strongly recommend or specify the admittance test (ISO 2931 / ASTM B457) for sealing quality, a non-destructive method. IS 1868 primarily specifies destructive tests like the acid dissolution test (IS 6012) and the dye spot test (IS 5523).
Key Similarities
≈Both IS 1868 and ISO 7599 use a similar system for classifying standard protective/decorative coatings based on minimum average thickness in micrometres (e.g., IS Grade AC 20 and ISO Class AA 20 both specify 20 µm).
≈All standards (IS, ISO, MIL) recognize the critical importance of sealing the porous anodic film to achieve desired corrosion resistance and color fastness, and all specify methods to test sealing quality.
≈The fundamental test methods for key properties like coating thickness (eddy current), abrasion resistance (Taber abraser), and sealing quality (acid dissolution) are based on the same principles across IS 1868 and its international counterparts.
≈For coloured anodic coatings intended for exterior use, both IS 1868 and ISO 7599 specify light fastness requirements using the Blue Wool Scale, ensuring long-term color stability against UV radiation.
Parameter Comparison
Parameter
IS Value
International
Source
Min. Thickness for Severe Exterior Use
25 µm (Grade AC 25)
25 µm (Class AA 25)
ISO 7599:2018
Sealing Quality (Acid Dissolution Test)
Mass loss ≤ 30 mg/dm² (Test per IS 6012)
Mass loss ≤ 30 mg/dm² (Test per ISO 3210)
ISO 7599:2018
Minimum Thickness for Hardcoat
50 ± 10 µm (Grade HA)
50.8 µm ± 20% (0.0020 in ± 0.0004 in) for Type III
MIL-PRF-8625G
Corrosion Resistance (Salt Spray)
To be agreed upon; no specific duration mandated for all grades.
336 hours minimum, no more than 15 isolated pits (for Type II coatings)
MIL-PRF-8625G
Light Fastness (Exterior Colour)
Minimum rating of 7 on Blue Wool Scale (per IS 2454)
Minimum rating of 8 (using a different class system for fastness, per ISO 2135)
ISO 7599:2018
Abrasion Resistance (Hardcoat)
Max 50 mg mass loss/1000 cycles (Taber, CS-17, 1000g)
Wear resistance specified by performance on specific alloys, typically verified by Taber test (ASTM D4060) as per contract.
MIL-PRF-8625G
⚠ Verify details from original standards before use