Phosphate conversion coating
Iron, zinc and manganese phosphate systems, substrate limits, coating mass and functional acceptance.
Tags: processes, finishing, conversion-coatings
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Removing 0.0600 g of dry phosphate from 0.0200 m² coated area gives 3.00 g/m² in the worked example. Counting only one face doubles it to 6.00 g/m². Use the specified selective removal method and verify local coverage, adhesion and finished dimensions separately.
What the process produces
Phosphating converts the metal surface. Baosteel describes a porous inorganic film on steel or zinc-coated steel that supports paint adhesion and under-film corrosion performance. Baosteel phosphating technology
ISO 9717:2024, edition 4, July 2024, specifies requirements for phosphate conversion coatings usually applied to ferrous materials, aluminum, zinc and their alloys. This broad substrate scope is not approval to run every alloy through one bath. Specify the substrate, coating family, function and post-treatment together. ISO 9717:2024
Families and bounded product examples
| Family | Primary-source example | Meaning for selection |
|---|---|---|
| Iron phosphate | Henkel describes BONDERITE M-FE as a non-crystalline, nonmetallic coating for paint adhesion and corrosion protection. | Identify the actual cleaner/coater arrangement and subsequent paint or powder system. |
| Zinc phosphate | BONDERITE M-ZN 952 A forms a fine crystalline zinc-phosphate layer containing manganese and nickel on steel, galvanized steel and Zn/Ni-coated steel. | “Zinc phosphate” can include other cations; confirm the product and substrate combination rather than assuming a pure zinc deposit. |
| Manganese phosphate | BONDERITE M-MN 5103 is an immersion process for iron and steel, especially low-alloy steel, intended to reduce friction and shorten running-in. | Define the lubricant and component qualification; the process name is not a universal friction coefficient or wear-life rating. |
The iron-phosphate description allows different line arrangements depending on the product. The zinc product is presented as a foundation for organic coatings and particularly electrocoat. The manganese product's corrosion-protection description explicitly includes anticorrosive oil or wax. These examples distinguish intended systems without ranking all iron, zinc and manganese formulations against one another. Henkel iron phosphating, M-ZN 952 A TDS, January 2020, M-MN 5103 TDS, February 2026
Trade names also need care. Chemetall's Gardobond portfolio includes phosphate families alongside chromate, oxalate and titanium/zirconium technologies. The brand alone therefore does not identify phosphate chemistry. Its AP 9809, for example, is described as a silane-based, phosphate-free pretreatment, despite being offered for applications that can include iron-phosphate lines. Do not silently substitute such a process where the drawing requires phosphate. Chemetall Gardobond portfolio, Chemetall AP 9809 product information
Preparation, conditioning and post-treatment
Cleaning and conditioning are distinct steps. Henkel's BONDERITE M-AC ZN is a titanium-containing conditioner used before phosphate conversion coating; its January 2024 sheet identifies iron, steel, aluminum, zinc and zinc-alloy surfaces and promotes fine-grained coating formation. It requires prior removal of oil, grease and foreign matter. The conditioner is not itself proof that a downstream phosphate product is qualified for every listed substrate. M-AC ZN TDS, pages 1–2
Surface history affects the result. The M-MN 5103 sheet states that cleaning chemistry changes phosphate crystallinity and that prior processing affects coating mass. Its sequence includes rinsing, activation or hot rinsing, phosphating, further rinsing, passivation and drying or oiling. Use the approved product instructions for the actual line; this example is not a generic bath recipe. M-MN 5103 TDS, pages 1–2
For a painted component, record the conversion layer, post-treatment, primer/topcoat, cure and test condition. For a moving component, identify the oil, wax or other lubricant and delivered condition. A bare phosphated coupon, an oiled component and a painted panel represent different systems. Require corrosion and friction results for the relevant system rather than transferring a result between them. The zinc and manganese product descriptions above explicitly connect their uses to subsequent organic coating or oil/wax. M-ZN 952 A, M-MN 5103
Coating mass is not a dimensional allowance
Coating mass per unit area is commonly expressed in g/m². Henkel gives a product-specific 5–40 g/m² range for M-MN 5103, dependent on previous processing. This is not a universal manganese-phosphate acceptance band. A mass per area is not a length: converting it to thickness requires an applicable density and a defensible model of the layer. Neither a bulk material density nor a universal outward-growth fraction is established by the process name. M-MN 5103 TDS, page 1
ISO 3892:2000 addresses gravimetric determination of conversion-coating mass per unit area. Select the applicable controlled method and preparation for the substrate and coating. Agree whether a test piece is measured before oil, wax or paint; otherwise a reported mass difference may include material other than the conversion layer. Record the total tested area, including both faces and any edges included in the measurement. ISO 3892:2000 record
Original bounded mass calculation
Assume the removal method isolates dry phosphate mass, with all coated surfaces counted and no contribution from substrate attack, retained liquid or other layers:
area-related coating mass = 0.0600 g / 0.0200 m² = 3.00 g/m².
One face would give 0.0600 / 0.0100 = 6.00 g/m². Use qualified inspection for local coverage, crystal morphology, adhesion and fit.
Acceptance and manufacturing handoff
Release the part with the substrate and condition, approved coating family/product, required post-treatment, significant surfaces, mass requirement and method, final dimensions and functional tests. Define whether coupons represent the actual parts and which delivered state is tested. Document surface preparation, rinse/conditioning stages and any subsequent cleaning or machining that could change that state.
A corrosion test needs its exposure method, duration, specimen preparation and acceptance criterion. A friction or running-in claim needs the actual mating material, lubricant and loading conditions. Do not translate a salt-spray result into a universal field life or treat black color as proof of coating mass. These are inspection-planning boundaries, not additional requirements attributed to the public ISO scope.
Source versions: ISO 9717 is edition 4, July 2024. ISO 3892 is edition 2, June 2000, last confirmed in 2021; its record shows the 2026 review has closed, without a published successor identified. Henkel PDF headers identify January 2020, January 2024 and February 2026 as cited above. Undated manufacturer web descriptions are distinguished from controlled product instructions. ISO 9717 record, ISO 3892 record