Zinc-aluminum 85/15 is the sacrificial coating bridges, water tanks, and transmission towers live on for thirty years. Arc- or flame-sprayed onto blasted steel at 4 to 10 mils, it combines zinc's galvanic protection with aluminum's barrier oxide — the Al phase slows zinc's dissolution, so the coating outlasts pure Zn in the mildly aggressive atmospheres most infrastructure sees.

We spray it per AWS C2.23M / NACE No. 12 / SSPC-CS 23 (and its ISO twin, ISO 2063-2:2017). The wire feeds through a twin-arc gun, droplets hit at ~3,680 psi bond strength, and build a dense two-phase structure — Al-rich particles surrounded by fine Zn — with 10-15% as-sprayed porosity that self-seals and responds well to a thin epoxy or acrylic sealer. Service envelope -50 to +200°C, up to 600°F before the Zn phase softens.

The service-life record is the selling point. FHWA's multi-year program found 6-mil 85/15 outperforming 40+ systems in salt-rich exposure, projecting 30-year maintenance-free life on most bridges. Norway's highway agency has 85/15 duplex systems 40 years in with no intervention.

This is not a wear coating — it's soft by design. Surface prep is non-negotiable: SSPC-SP 10 near-white, 2.5-4.0 mil profile. Send us the structure and exposure category — we'll tell you if 85/15, pure Zn, or aluminum is right, and quote it to AWS C2.23.

Technical data

Hardness: R15T 85 (approx. RB 73, Knoop100 converted); soft sacrificial alloy — not a wear coating. Reported Vickers 90-140 HV depending on spray method and alloying; twin-wire arc spray Al-Zn-Mg variants measured ~135 HV
Bond strength: ~3,680 psi (25.4 MPa) on blasted steel per A&A datasheet; typical field arc/flame spray Zn, Al, and Zn-Al coatings run 800-2,000 psi (5.4-13.6 MPa) per ASTM D4541 pull-off testing in AWS C2.23 qualified work
Max service temp: 600°F (315°C) — well above pure zinc's ~250°F / 120°C ceiling; Al phase raises the upper service limit. ISO 2063 protection range -50°C to +200°C (-58°F to +392°F) for atmospheric corrosion service
Max service temp: 315°C practical; 200°C per ISO 2063 corrosion-protection envelope
As-sprayed porosity: ~10-15% typical as-sprayed for twin-wire arc and flame spray; 85/15 runs markedly denser than pure Zn — published studies show ~3x porosity reduction vs pure zinc because the Al phase has higher melting point and surface tension, producing finer, more rapidly self-sealing pores
Typical thickness: 4-10 mils (100-250 µm); FHWA and AWS C2.23 bridge work standardizes on 6 mils (150 µm) as the reference thickness; 8-10 mils used for CX / Im2 marine and immersion service
Density: 4.97 g/cm³ (~91% of theoretical); coating weight 0.0484 lb/ft²/mil (0.593 kg/m²/100µm)

Where it earns its keep

30+ years of documented service life on bridges, water tanks, and dam locks without major repair — Norwegian Public Roads Administration has metallized bridges in continuous service 40+ years with duplex topcoats
Galvanic sacrificial protection like pure zinc or TSA, but with markedly longer service life in mildly aggressive environments — the Al phase slows Zn dissolution and adds barrier oxide
ISO 2063-1/-2:2017 and AWS C2.23M/NACE No. 12/SSPC-CS 23 specified — the default thermal spray corrosion chemistry for infrastructure worldwide
Denser, more self-sealing than pure Zn — ~3x lower porosity in published deposition studies, so pore sealing with vinyl, acrylic, or thin epoxy is highly effective and often cheap insurance
Duplex (TSC + topcoat) systems deliver 1.5 to 2.3x the additive life of either system alone — lowest lifecycle cost corrosion strategy documented in FHWA and NPRA long-term data
Field-applicable at any scale — unlike hot-dip galvanizing, no size limit; sprayed on the bridge, tower, or tank in place, with repair and tie-in straightforward

Where it doesn't

Soft coating — not a wear or abrasion surface; high-traffic walkways, scrape zones, and impact areas need a topcoat or hard overlay
As-sprayed porosity (~10-15%) leaves the coating permeable; immersion and marine service almost always require a sealer to realize full service life
Surface preparation is non-negotiable — SSPC-SP 10 near-white blast, profile 2.5-4.0 mils, and spray within the specified humidity and holding window per AWS C2.23; shortcutting prep is the #1 premature-failure mode
Applicator qualification matters — AWS C2.23 / C2.16 operator and procedure qualification records, bend tests, and cut/pull adhesion testing are standard on bridge work
Lower cathodic driving voltage than pure Zn — in very-heavy-chloride or continuous seawater immersion, pure Zn or TSA can be a better pick; 85/15 shines in atmospheric C4-C5 and intermittent wet service
Heat-affected zones above ~315°C (600°F) degrade the coating; not suitable for furnace steel, hot stacks, or uninsulated high-temperature piping

Sources

Data points on this page draw on the following published references. Nothing here replaces a material-specific review by our process engineers — but it's the working starting point.

A&A Company — Metallized 85/15 Zinc-Aluminum Thermal Spray Coating Technical Data
“Hardness R15T 85 (RB 73) converted from Knoop100; bond strength 3,680 psi (25.4 MPa) on blasted steel; density 4.97 g/cm³ (91%); coating weight 0.0484 lb/ft²/mil; melting point ~440°C; max service temperature 600°F (315°C); deposit efficiency 70%; coating texture 200-350 Ra; two-phase structure of large Al-rich particles surrounded by fine Zn particles; very fine pores with rapid natural sealing; 22% greater coverage per pound than pure zinc.”
ISO 2063-2:2017 — Thermal spraying — Zinc, aluminium and their alloys — Part 2: Execution of corrosion protection systems
“Specifies requirements for corrosion protection of steel structures, components or parts coated by thermal spraying of zinc, aluminium or their alloys. Covers application temperature range -50°C to +200°C. Applies to new fabrication in the workshop, on-site, and repair on-site after assembly. Specifies surface preparation, thermal spraying, testing, and post-treatment (sealing) requirements, plus coating thickness, minimum adhesive strength, and surface conditions.”
AWS C2.23M/C2.23:2018 / NACE No. 12 / SSPC-CS 23 — Specification for the Application of Thermal Spray Coatings (Metallizing) of Aluminum, Zinc, and Their Alloys and Composites for the Corrosion Protection of Steel
“Joint AWS/NACE/SSPC standard covering application of metallic thermal spray coatings of aluminum, zinc, and their alloys and composites for corrosion protection of steel. Specifies surface preparation, coating application, repair of coating defects, coating thickness measurement, adhesion testing, and application of sealers and topcoats. Intended for facility owners and specifiers developing project specs for preservation and maintenance of steel structures and components.”
STRUCTURE Magazine — Metallized Coatings for Corrosion Control (Kogler, Maguire)
“Metallized zinc and 85/15 zinc-aluminum coatings provide 25+ years before first maintenance (5% steel surface rust). FHWA tested 47 coating systems; metallized systems consistently provided the best performance with no corrosion failure in aggressive salt-rich environments over 5-6.5 year exposures. 6 mil coatings outperformed over 40 other systems. Coatings applied up to 10 mils (254 µm). References NACE SP0216-2016 and SP0290-2007.”
Thermion — Thermal Spray Coatings for DOT / FHWA Bridge Metalizing
“FHWA: properly applied metallized coatings (zinc, 85% Zinc/15% Aluminum, and Aluminum) of at least 6 mils thickness provide at least 20 years of maintenance-free corrosion protection in wet, salt-rich environments and are expected to provide 30 years of protection in most bridge exposure environments. 85/15 alloy produces the best anti-corrosion characteristics of both zinc and aluminum.”
Thermal Spray Zinc (International Zinc Association) — Bridges Project Page
“Norwegian Public Roads Administration (NPRA) has used zinc thermal spray with paint topcoat (duplex) for steel bridges since the 1960s; bridges exposed 40 years without maintenance; typical first maintenance ~35 years, far longer than a 3-layer paint system. Duplex coatings deliver 1.5-2.3x the sum of the individual expected lives. Bridge interiors of potable water tanks, pipelines, and dam locks show over 30 years of service without major repair.”
Journal of Materials Science — Deposition and Corrosion Studies of Plasma Arc Thermal Sprayed Zn and 85Zn-15Al Films on Steel (Jiang et al., 2022)
“85Zn-15Al deposited film shows a dense two-phase structure with roughly 3x reduced porosity vs pure Zn, attributed to the higher melting point and surface tension of aluminum which enhance bond adhesion. Zn-15Al offers superior long-term corrosion protection to steel in aggressive atmospheric and marine conditions versus pure Zn.”
Zinacor — Thermal Spray with Zinc and Zinc-Aluminium (ISO 2063 / ISO 12944)
“Zinc-Aluminium (85/15) offers superior atmospheric corrosion resistance vs pure zinc, better performance in SO2-rich atmospheres and chloride environments, and ~30% less wire consumption for equivalent coverage. Metallising provides triple protection: barrier layer, patina oxidation, and cathodic sacrificial protection. Immediate sealer/paint post-metallising prevents oxide contamination — epoxy and polyurethane recommended over alkyd resins.”

Material data on this page is provided as a general reference and can vary by lot, substrate, and application. Contact HTS to confirm the right material and specification for your specific part.

Zinc Aluminum

Technical data

Where it earns its keep

Where it doesn't

Typical applications

Wear modes addressed

Industries

Substrates

Sources

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