What Metals Can Be Powder Coated?

Almost every metal a manufacturer or fab shop sends out for finishing can be powder coated. The better question for an engineer or buyer is what each metal needs before the powder goes on, and whether anything attached to the part will survive the oven. This guide works through the common substrates one at a time, then covers the parts that should not go through a production powder line.

If you want the background on how the process works first, start with what powder coating is and how it cures.

The two conditions every part has to meet

Conventional industrial powder coating is electrostatic spray followed by a heat cure. That sets two requirements for the part:

1. It has to ground. The gun charges the powder, and the grounded part attracts and holds it until cure. A part that cannot carry the charge away to ground coats unevenly, if at all. This is why metal is the natural substrate.
2. It has to survive the cure. What matters is time at metal temperature. On our line that is typically around 400°F at the part, depending on the powder. Cardinal’s standard powders cure about 10 minutes at 400°F, and its superdurable lines can cure lower, around 350°F. Heavy parts take longer to come up to temperature, so they spend more time in the oven than the cure schedule alone suggests.

Our process is built for metal parts that can be electrically grounded and withstand the cure temperature. Every metal below meets both conditions. The differences are in surface prep.

Quick reference by substrate

Metal by metal

Carbon steel

Steel is the default powder coating substrate. Cardinal’s data sheets describe its standard powders as designed for electrostatic spray on steel, galvanized steel or aluminum, and most published test data comes from phosphated steel panels.

Cold-rolled steel is the easy case: clean off the oil and shop dirt, pretreat, coat. Iron phosphate is the long-standing workhorse pretreatment for steel, and zinc phosphate, a heavier conversion coating, is also common.

Hot-rolled steel adds mill scale, a brittle oxide layer that can crack or flake away from the steel and take the coating with it, and that can trap moisture that escapes during cure. When scale or rust has to come off, the usual answer is an abrasive blast. We coordinate blasting through our partner as part of the coating job, so it stays on one quote and one PO. Laser-cut edges with heavy oxide fall into the same category.

Aluminum

Yes, you can powder coat aluminum, and it is one of the most common powder coating substrates. Two things are different from steel.

Pretreatment has to suit aluminum. According to Products Finishing, iron phosphate is ineffective on aluminum. Aluminum is normally treated with a chrome or non-chrome conversion coating, or a zirconium-type pretreatment. If your drawing calls out a specific conversion coat, such as MIL-DTL-5541 chem film, put it on the RFQ and note whether parts will arrive already treated, so we can plan the prep and confirm how that step is handled.

Check heat-treated alloys against the cure. A 2009 study in the Journal of Materials Engineering and Performance coated 2024-T3, 6061-T6 and 7075-T6 at two cure temperatures. Both cures produced acceptable coatings, but the higher-temperature cure negatively affected the alloys’ mechanical properties. For a bracket or a cover this rarely matters. For a structural or load-rated aluminum part, have your engineer confirm the temper can take a cure around 400°F at the part, or ask whether a lower-cure powder fits the spec.

One product note: Cardinal’s zinc-rich epoxy primer is for steel and galvanized steel only, not aluminum. If a two-coat system is specified for an aluminum part, the primer has to be one rated for aluminum.

Architectural aluminum (storefront, curtain wall) often carries FGIA/AAMA 2604 or 2605 performance specs that require particular powder chemistries and recognized pretreatments. Those are worth reading closely before you quote that kind of work with anyone.

Galvanized steel

Galvanized sheet and galvanneal are routine substrates, but they are zinc surfaces, not steel. Iron phosphate is ineffective on galvanized, so the pretreatment has to be one that works on zinc.

Hot-dip galvanized (HDG) parts take more care. Powder over HDG is called a duplex system, and surface prep is covered by ASTM D7803. The American Galvanizers Association’s guidance includes a few steps buyers can act on directly:

• Tell your galvanizer the parts will be powder coated. They should skip the water quench or chromate passivation bath, which the AGA says interferes with powder adhesion and can lead to blisters and peeling.
• Expect dross bumps and high spots to be ground flat.
• Expect a light sweep blast (SSPC-SP 16 for non-ferrous metals) or a chemical treatment to give the zinc a profile. When a blast is needed, we coordinate it through our blasting partner as part of the coating job.
• Expect a pre-bake. HDG traps gas that escapes during cure as pinholes. Sources disagree on how hot: Cardinal’s data sheet says to degas galvanized steel 5 degrees above cure temperature, while the AGA recommends about 54°F (30°C) above cure for at least an hour. The right cycle depends on the part, and we run outgas pre-bakes in-house.

Our guide to powder coating galvanized steel and castings goes deeper on duplex systems and pinholing.

Stainless steel

Yes, you can powder coat stainless steel, but it does not take a chemical pretreatment the way steel does. As one Products Finishing answer puts it, “Stainless steel is chemically inert so there is no good chemical treatment for adhesion of a powder.” The bond has to be mostly mechanical.

The standard approach is a media blast to roughen the surface, without going so aggressive that the texture shows through the finish. Because the surface is now rough, the film has to be thick enough to cover the peaks of the profile. A smooth or polished stainless finish straight from the mill gives the coating very little to hold.

For a buyer, that means stainless usually adds a blast step that mild steel of the same size may not need. We coordinate that blast through our partner as part of the coating job, and the quote reflects it. Put the grade and the as-received finish on the RFQ so the prep is priced correctly.

Cast iron and cast aluminum

Castings coat well once the gas is out of them. Cast iron and cast aluminum are among the most common outgassing problems in powder coating: air, moisture and oil trapped in the porosity expand during cure and push pinholes or blisters through the film. Products Finishing puts it plainly: “The root cause is trapped porosity in the casting.”

The usual defenses are:

• An outgas pre-bake at or above the cure temperature, so the gas escapes before the powder goes on. Dirty or oil-soaked castings can need more than one cycle.
• Film build control, because a heavy film makes it harder for gas to release.
• An anti-gassing primer in difficult cases. Cardinal makes an anti-gassing primer for outgassing-prone parts. It adds a coat, so it adds cost, and we quote it as a two-coat system.

Results vary with casting quality. Pre-baking ranges from very effective to not effective at all depending on the part, so on a new casting program it is worth coating a few first-article parts before the full release.

Other metals

Cardinal lists magnesium among the substrates its powders are used on. For magnesium, copper, brass and other less common metals, prep depends on the alloy, so we evaluate them case by case. Send the alloy, the drawing and, ideally, a sample part.

What cannot go through our process

Some parts are metal but still should not go into the oven as they are. Others are not metal at all.

Assemblies with non-metal components

Most rubber seals and gaskets, plastic fittings, belts, grease-packed bearings, wiring and electronics will not survive a cure around 400°F unless the component is rated for that temperature. Products Finishing notes that even many low-cure polyester powders still cure above about 300°F, which will most likely damage rubber, plastic and similar materials. The options are:

• Coat the metal parts before assembly, which is usually the cleanest answer
• Remove the components before coating and reinstall after
• Use a lower-temperature liquid paint system instead, which we also offer

Our comparison of powder coating vs. liquid paint covers when wet paint is the better choice.

Non-conductive substrates

Powder can be applied to MDF, some plastics, composites, wood and glass. That is real and well documented by the Powder Coating Institute and Products Finishing. It uses different equipment: low-cure powders (for example, MDF powders that cure around 265°F in catalytic infrared ovens), UV-cure powders, preheating to make the part attract powder, or conductive primers.

That is a specialty line. Ours is a metal-finishing line, built for parts that ground and take a full cure. If your part is MDF or molded plastic, look for a coater who runs low-cure or UV equipment.

Parts the oven cannot fit

We run a large batch oven that takes parts up to roughly the size of a large cabinet or a long frame. Send the dimensions and weight, and we will confirm fit before we quote. Part geometry matters too: deep channels and tight inside corners are harder to coat, and our guide to designing parts for powder coating covers how to avoid problems at the drawing stage.

What to put on the RFQ about the metal

The substrate drives the prep plan, and the prep plan drives price and lead time. Give your coater these details up front, or include them when you request a quote along with your drawings:

• Material, alloy and temper, for example 6061-T6 aluminum, 304 stainless, or A36 hot-rolled steel
• Incoming condition: oiled, rusted, scaled, laser-cut, machined, plated, or already conversion coated
• Whether it is cast or hot-dip galvanized, and who the galvanizer is if you want quench and passivation skipped
• Any non-metal components still on the part
• Heat limits, if engineering has set a maximum part temperature
• The coating spec, including any primer, film thickness or pretreatment callout

We review RFQs against the drawing and spell out the prep each part needs in the quote. For more on the cleaning, pre-bake and masking steps we run in-house, see our prep and masking page.