IS 1573:2018 is the Indian Standard (BIS) for electroplated coatings of zinc on iron and steel. IS 1573 covers electroplated zinc coatings on steel and iron — the most common corrosion protection for fasteners, brackets, and small steel components. Coating thickness ranges from 5µm (mild indoor) to 25µm (severe outdoor).
Specification for electroplated zinc coatings on iron and steel articles for corrosion protection covering coating thickness, adhesion, and appearance.
Key reference values — verify against the current code edition / project specification.
| Reference | Value | Clause |
|---|---|---|
| Subject | Electroplated zinc coating on iron/steel | Scope |
| Service grades | Coating thickness by service condition (mild→severe) | Classes |
| Passivation | Chromate/passivation for added protection | Finish |
| Tests | Thickness, adhesion, appearance, salt-spray | QC |
| vs hot-dip | Thinner than hot-dip — lighter duty/decorative | Note |
| Read with | IS 2629 / IS 4759 (hot-dip galvanizing) | Cross-ref |
IS 1573:2018 is the Indian Standard for Electroplated Coatings of Zinc on Iron and Steel — Specification. It is the zinc electroplating specification for indoor fasteners, small parts, and decorative / corrosion-protective applications.
Use it when: - Specifying electroplated fasteners — Property Class 4.8 / 5.8 / 8.8 bolts for indoor / general applications - Procuring zinc-plated small parts — washers, nuts, brackets, springs, fittings - Auditing electroplating supply — coating thickness, adhesion, salt-spray performance - Investigating premature corrosion — zinc coating failures from under-plating or post-plating treatment issues
Key differences vs hot-dip galvanizing (HDG):
| Property | Electroplating (IS 1573) | HDG (IS 1367 Part 3) | |---|---|---| | Thickness | 5-25 μm typical (limited by process) | 25-100 μm typical | | Service life (atmospheric) | 5-15 years | 20-50+ years | | Surface finish | Smooth, uniform; can be passivated for various colors | Crystalline 'spangle' pattern; matte gray | | Application size | Small to medium parts (limited bath size) | Any size including structural sections | | Hydrogen embrittlement risk | Yes — significant; requires baking | Yes — for high-strength bolts | | Cost | Lower per kg of zinc | Higher per kg; better lifecycle for outdoor | | Visible markings | Coating may obscure stamped markings | Bright zinc surface clearly visible |
Application categories: - Indoor protective: Class 1 (lowest; 5-12 μm); for assembly fasteners, indoor brackets, light-duty machinery - Indoor decorative: Class 2 (medium); for visible components, decorative fasteners - Limited outdoor: Class 3 (high); for non-marine outdoor applications with periodic maintenance - Premium / aggressive: Class 4 (highest); for outdoor + post-coating treatment (chromate / passivation)
Companion codes: - IS 1367 Part 3:2002 — Hot-dip galvanized coatings on fasteners (the HDG alternative) - IS 4826:1979 — Hot-dip galvanized coatings on round steel wires - IS 2629:1985 — Hot-dip galvanizing of iron and steel (HDG general) - IS 4759:1996 — Hot-dip zinc coatings on structural steel - IS 277:2018 — Galvanized steel sheets
Coating thickness classes (Clause 4):
| Class | Min thickness (μm) | Typical use | |---|---|---| | Service Condition 1 (lowest) | 5 | Indoor, dry, non-corrosive (e.g., file cabinets, light machinery) | | Service Condition 2 | 10 | Indoor with occasional humidity (e.g., bathroom hardware, kitchen) | | Service Condition 3 | 15 | Limited outdoor, sheltered (e.g., porch hardware, light outdoor) | | Service Condition 4 | 25 | Outdoor with mild exposure (with post-coating treatment) |
Coating mass equivalent: - 5 μm = ~35 g/m² zinc - 10 μm = ~70 g/m² - 25 μm = ~180 g/m²
(Compare with HDG sheet IS 277 at Z120-Z350 = 120-350 g/m² for sheet; HDG fasteners at 50-100 g/m². Electroplated zinc significantly thinner.)
Post-coating treatment (Clause 5) — improves corrosion resistance: - No post-treatment: bright zinc finish; basic corrosion resistance - Yellow chromate passivation: golden tint; ~3-5× corrosion improvement; classic 'gold zinc' look - Olive drab chromate: military finish; high corrosion resistance - Black chromate: black finish; specialty use - Phosphate + oil: oily surface; for paint base or temporary protection
Note: hexavalent chromate (yellow / olive drab) is being phased out globally due to environmental + health concerns. Trivalent chromate alternatives are accepted under EN 12451-2 and gradually being adopted in India.
Acceptance tests (Clause 6):
The mechanism: electroplating involves cathodic deposition of zinc; the process generates atomic hydrogen at the steel surface; some hydrogen diffuses into the steel. For high-strength steels (≥ 1000 MPa UTS, i.e., property class ≥ 10.9), this absorbed hydrogen causes delayed brittle fracture under sustained tensile stress.
Risk profile: - Property Class 4.6, 5.6, 5.8, 6.8: LOW risk (low tensile strength) - Property Class 8.8: MODERATE risk (some hydrogen embrittlement possible) - Property Class 10.9: HIGH risk (significant; mandatory mitigation) - Property Class 12.9: VERY HIGH risk (electroplating largely avoided in IS practice)
Mitigation per IS 1573:2018: - Baking treatment after plating: - 200-230°C for 4 hours minimum (property class 10.9) - 200-230°C for 8 hours (property class 12.9) - Removes ~80-95% of absorbed hydrogen - Mechanical galvanizing as alternative (cold-process; no hydrogen) for property class ≥ 10.9 - Zinc-aluminium flake coatings (Geomet, Dacromet) — no hydrogen risk; trickier process but safer
Field observation: hydrogen-embrittled fasteners typically fail 24-72 hours after tightening, not immediately on installation. A bolt looks fine when torqued; head pops off under sustained service load within days. This is the classic 'delayed failure' that has caused many structural / mechanical accidents.
For specifying engineers: - For property class ≥ 10.9: specify post-plating baking certificate (4+ hours at 200-230°C) - Consider mechanical galvanizing or zinc-flake coatings for property class 12.9 - Avoid electroplated high-strength fasteners for safety-critical applications
1. Specifying electroplating for outdoor / coastal applications — IS 1573 electroplated zinc lasts only 5-15 years outdoor; HDG (IS 1367 Part 3 / IS 277) lasts 20-50+. For permanent outdoor + marine applications, use HDG.
2. Skipping post-plating treatment — bare electroplated zinc has limited corrosion resistance; passivation extends life 3-5×. Always specify passivation type (yellow chromate, olive drab, trivalent chromate, etc.).
3. Skipping baking for high-strength fasteners — Property Class 10.9+ MUST be baked after plating to release absorbed hydrogen. Many small electroplating shops skip this; failures occur in service.
4. Wrong coating thickness for environment — 5 μm zinc on a part used in humid bathroom: rust within 6-12 months. Match thickness to actual service exposure.
5. No salt-spray verification — IS 1573 acceptance includes salt-spray test (24-200 hours by class). Without this verification, coating quality is unknown.
6. Visual inspection only — 5 μm vs 25 μm zinc look identical to naked eye. Always use magnetic gauge or chemical strip test for thickness verification.
7. Mixed electroplated + HDG fasteners in same connection — different coating thicknesses, different corrosion potentials; galvanic effect can accelerate corrosion at the junction. Standardize on one finish per joint.
8. Storage in humid / cold conditions — electroplated parts left in humid yards or cold storage rooms develop white rust (zinc carbonate) — surface oxidation. Cosmetic issue + slight loss of protection. Store dry, room temperature.
9. Specifying 'zinc plated' without grade — there's no such thing as generic zinc plating; specify class (1-4) + thickness + treatment + IS 1573:2018 reference.
10. Cutting / drilling electroplated parts on site — exposes bare steel at cut/drill location; localized corrosion. Pre-fabricate all openings; for field modifications, apply zinc-rich paint to exposed steel.
IS 1573:2018 is the current revision (replacing IS 1573:1991 / 2003 revisions). The 2018 revision: - Aligned with ISO 4042:2018 international practice - Added trivalent chromate passivation as approved post-treatment alternative - Tightened hydrogen embrittlement testing requirements - Updated acceptance test methods
Indian electroplating market: - Major fastener manufacturers (Sundram Fasteners, Lakshmi Machine Works, Punjab Fasteners): in-house electroplating per IS 1573 + IS 1367 Part 3 + alternative coatings. Multiple options + traceable quality. - Specialty electroplating job-works: regional facilities serving smaller manufacturers; quality varies; sample testing recommended. - Imported pre-plated fasteners (Korean, Chinese): widely available; verify IS 1573 + IS 1367 equivalence.
Cost reality (2026 typical Indian market): - 5 μm zinc plated fastener (Class 1): baseline cost (~10-30% premium over bare) - 10-15 μm zinc plated (Class 2-3) + yellow chromate: ~30-60% premium over bare - 25 μm zinc plated (Class 4) + passivation + baking: ~80-150% premium over bare - Hot-dip galvanized (premium alternative): comparable to Class 4 electroplated
For specifying engineers: - Indoor general applications: Class 2 zinc plated + yellow chromate (cost-effective) - Bathroom / kitchen hardware: Class 3 + chromate - Limited outdoor: Class 4 + chromate, or move to HDG - Permanent outdoor: HDG (IS 1367 Part 3); avoid electroplating - High-strength fasteners (Class 10.9+): mandate post-plating baking (4+ hours at 200-230°C) OR use mechanical galvanizing / zinc-flake
Quality assurance: - Manufacturer's IS 1573:2018 conformance certificate - Sample salt-spray test per batch (24-200 hours per Class specification) - Magnetic gauge thickness verification on random sample - Hydrogen embrittlement test certificate for property class ≥ 10.9 fasteners - Storage in dry, controlled environment; periodic inspection
Environmental + health considerations: - Hexavalent chromate (yellow / olive drab) is carcinogenic + environmental hazard - EU REACH + RoHS regulations restrict hexavalent chromate in many applications - Trivalent chromate alternatives now widely available — slightly less corrosion resistance but environmentally compliant - Some sites require RoHS-compliant fasteners; verify before procurement for export-grade work
Future direction: - Trivalent chromate replacing hexavalent for all applications (environmental driver) - Zinc-aluminium electroplating (high-performance alternative; better corrosion resistance than pure zinc) - Zinc-nickel alloy plating (premium; excellent corrosion + paint-base; growing market) - Mechanical galvanizing for high-strength fasteners (no hydrogen embrittlement)
IS 1573 remains the working specification for indoor zinc-plated fasteners + small parts. The market is mature; quality is reliable from premium suppliers; for any application requiring extended outdoor service, HDG or premium alternative coatings are the practical choice over electroplating.
| Parameter | IS Value | International | Source |
|---|---|---|---|
| Fe/Zn 12 thickness | Min 12 µm | Min 12 µm | ISO 2081 |