Metalizing: Zinc and Aluminium Arc Spray for Long-Life Corrosion Protection

What Is Metalizing?

Metalizing is the application of a zinc, aluminium, or zinc-aluminium alloy coating onto steel by arc spray, a thermal spray process that melts two continuously fed wires in an electric arc and atomizes the molten metal onto the substrate with a compressed-air jet. The result is a metallic coating, typically 100–250 microns thick, that protects the underlying steel from corrosion both by acting as a physical barrier and, more importantly, by corroding preferentially to the steel itself — a property called cathodic (sacrificial) protection. Metalizing is the industrial name for thermal spray zinc (TSZ) and thermal spray aluminium (TSA), the standard long-life corrosion protection systems for structural steel, storage tanks, bridges, and marine and offshore hardware.

Metalizing sits apart from the wear-focused end of the thermal spray family — HVOF, D-Gun, and plasma spray — which build hard, dense carbide or ceramic coatings for abrasion and erosion resistance. Arc spray runs at lower particle velocity and produces a coating with higher porosity, but for corrosion protection that porosity is not a defect: it gives the coating more surface area to sacrifice before the steel underneath is ever exposed. For where metalizing fits against the rest of the thermal spray family, see our guide on what thermal spray coating is.

How Arc Spray Metalizing Works

An arc spray gun feeds two wires of the coating metal — zinc, aluminium, or a zinc-aluminium alloy — toward each other at a controlled rate. A DC electric arc struck between the wire tips melts the metal continuously at the point of contact, and a compressed-air jet atomizes the molten metal into fine droplets and propels them onto the substrate at roughly 100–200 m/s. On impact, the droplets flatten and interlock into overlapping splats, building a coating of the specified thickness pass by pass.

Because the process runs on wire feedstock rather than powder and needs only compressed air rather than combustion gas or plasma, arc spray equipment is comparatively simple and portable, which is why metalizing is routinely done in the field on bridges, tanks, and structural steel as well as in the shop. Surface preparation is critical to coating life: the steel must be abrasive-blasted to a near-white or white metal finish (typically Sa 2½ or Sa 3) immediately before spraying, since the coating's adhesion is entirely mechanical — it keys into the roughened profile rather than metallurgically bonding or diffusing into the substrate.

Why Metalizing Outlasts Paint

Paint and organic coatings protect steel purely as a barrier: as long as the film is intact, moisture and oxygen are kept off the steel, but any breach — a scratch, a pinhole, a chip from impact — becomes a corrosion site that spreads underneath the coating. A zinc or aluminium metalized coating protects two ways at once. It is a barrier, and where the barrier is breached, the zinc or aluminium corrodes sacrificially, generating corrosion products that are less electrochemically active than steel and continuing to protect the exposed steel at the breach point until the surrounding metal coating is consumed.

That sacrificial behaviour is why properly applied and sealed metalizing systems are documented in maintenance-free service for 20–30+ years in atmospheric exposure, several multiples of a typical paint system's repaint interval. The tradeoff is upfront cost and surface preparation requirements — abrasive blasting and arc spray application cost more per square metre than paint — which is why metalizing is specified where repainting is expensive, hazardous, or logistically difficult: elevated steel structures, offshore platforms, and tank interiors, rather than low-consequence indoor equipment.

Zinc vs Aluminium: Choosing the Metalizing Material

Zinc and aluminium are both sacrificial to steel, but they are not interchangeable, and the choice is an engineering decision driven by the service environment.

| Coating | Sacrificial Rate | Best Environment | Typical Thickness | Notes | |---|---|---|---|---| | Zinc (TSZ) | Faster-consuming, strongly sacrificial | Atmospheric, mildly corrosive, freshwater | 100–200 microns | Most common general-purpose choice; excellent cathodic protection | | Aluminium (TSA) | Slower-consuming, longer-lived barrier | Marine, offshore, high-chloride, high-temperature (to ~480°C) | 150–250 microns | Preferred for splash-zone and seawater immersion; better heat tolerance | | Zinc-Aluminium alloy (85/15) | Balanced | General atmospheric and mixed exposure | 100–200 microns | Combines zinc's faster sacrificial action with aluminium's longer barrier life |

Zinc is the default for general atmospheric protection because its sacrificial action is fast and forgiving of minor coating damage. Aluminium is specified where chloride exposure is severe — splash zones, seawater immersion, offshore structures — because it forms a more stable, longer-lived protective oxide and tolerates higher service temperatures. The 85/15 zinc-aluminium alloy is a common middle ground where a project wants zinc's sacrificial reliability with some of aluminium's extended service life.

Sealing and Topcoating Metalized Coatings

As-sprayed metalizing typically runs 5–15% porosity, higher than the wear-coating processes because arc spray's lower particle velocity produces less mechanical compaction on impact. For most structural corrosion applications this porosity is sealed rather than left open, both to extend coating life by slowing the rate of sacrificial consumption and, where appearance matters, to accept a paint topcoat.

A vinyl or epoxy sealer is typically applied within hours of spraying, before the fresh metal surface oxidizes and while the pores are still receptive to penetration. Where a specific colour or additional barrier protection is wanted, a compatible paint system can then be applied directly over the sealed metalizing — a duplex system that combines the metal coating's decades-long sacrificial protection with the topcoat's appearance and added barrier life, materially outlasting either system alone.

Where Metalizing Is Used

Metalizing is specified wherever steel needs long-term, low-maintenance corrosion protection and the cost of coating failure — structural risk, downtime, inaccessibility for repainting — outweighs the higher upfront application cost. Typical applications include:

• Bridges, transmission towers, and other elevated structural steel where repainting access is difficult and expensive
• Storage tank exteriors and interiors, including potable water and fuel storage
• Offshore platforms and marine structures in the splash and atmospheric zones, typically with aluminium (TSA)
• Power plant structural steel and boiler auxiliary equipment exposed to outdoor atmospheric corrosion
• Pipe supports, handrails, and structural steel in chemical and process plants with corrosive atmospheres
• New-build structural steel specified for a 25+ year maintenance-free corrosion protection life cycle

Selecting a Metalizing Specification: A Checklist

Before specifying a metalizing job, work through these questions:

• What is the exposure environment — atmospheric, freshwater, or marine/chloride? This decides zinc vs aluminium vs the 85/15 alloy.
• What service life is required, and is repainting access realistic during that life? Low-access structures justify metalizing's higher upfront cost.
• Is a sealer or duplex paint topcoat required for appearance or added barrier life, and is it compatible with the metal coating and any downstream coating?
• Can the component reach the required surface preparation standard (near-white or white metal blast) immediately before spraying, in the shop or in the field?
• Does the component see elevated temperature? Aluminium tolerates higher service temperatures than zinc before its sacrificial action degrades.
• Is this new-build steel or a repair/refurbishment of an existing structure with prior coating history that needs to be fully removed first?

Common Mistakes When Specifying Metalizing

Metalizing failures are almost always preparation or sealing errors rather than process errors. The mistakes below recur across structural steel corrosion protection projects.

• Skipping or under-specifying abrasive blast preparation — since adhesion is purely mechanical, any residual mill scale, rust, or contamination on the surface will cause the coating to disbond in service
• Leaving as-sprayed porosity unsealed in a wet or immersed environment — unsealed 5–15% porosity lets moisture reach the steel substrate faster than intended, shortening service life
• Choosing zinc for high-chloride marine or offshore splash-zone exposure where aluminium's slower, more stable sacrificial action is the better fit
• Applying a topcoat before the sealer has cured or without confirming paint compatibility with the metal coating, risking topcoat disbondment
• Treating metalizing as a drop-in paint replacement on a project timeline — surface prep and application logistics for arc spray differ meaningfully from a painting crew's workflow and need to be planned accordingly

Get a Quote for Metalizing

Lotus Surface Tech is an ISO 9001:2015-certified thermal spray facility in Chennai, Tamil Nadu, established in 2015, operating an arc spray/metalizing line alongside Super-D-Gun, HVOF, plasma spray, and flame spray, with capacity for components up to Ø800 mm × 7 m. We work with plant engineering and procurement teams across power generation, oil and gas, and heavy industrial sectors to specify and apply zinc and aluminium metalizing for long-life corrosion protection.

Full process capability detail is on our technologies page. If your application is wear rather than corrosion, our what is thermal spray coating guide covers the full process family, including where HVOF and D-Gun fit against arc spray. When you are ready to move forward, contact us to get a quote — share your component or structure, the exposure environment, and required service life, and we will recommend the right material and sealing system.