Powder Coating for Hybrid and 3D Printed Metal Parts

By Steve Ladatto

For the powder coating industry, the evolution of additive manufacturing brings exciting new opportunities and significant challenges. As 3D printed and hybrid-manufactured metal parts move into mainstream production, finishers are discovering how to adapt pretreatment, coating and curing processes to achieve the same durability, aesthetics and sustainability that have long defined powder coating’s success in traditional manufacturing.

Powder coating is increasingly being explored as a viable surface finish for AM metal parts. In hybrid workflows, where additive and subtractive techniques are combined, the role of powder coating extends beyond aesthetics, offering corrosion resistance, wear protection and even thermal management. Yet the application of powder coating to AM surfaces is far from straightforward. However, there are strategies to create a successful and less challenging process.

Additively manufactured metal parts present a very different surface profile than traditional rolled or machined substrates, posing unique challenges for powder coating. The layer-by-layer build process often leaves a visibly rough texture, with roughness average (RA) values that can exceed 10–15 µm. This surface roughness results from partially melted powder particles, the stair-stepping effect inherent to additive layering, and the resolution limits of the 3D printing process itself. While such texture can enhance mechanical anchoring for coatings, it also increases the risk of air entrapment and uneven coating flow.

During the powder coating cure cycle, typically between 320°F and 392°F (160°C and 200°C), these trapped gases expand and escape through the film, creating pinholes, craters or other surface defects. The challenge lies in balancing the natural adhesion benefits of a rough AM surface with the need for a smooth, defect-free finish. Without proper surface preparation or densification, the porosity and irregularities can lead to inconsistent film builds and compromised aesthetics.

Because of powder coating’s benefits, manufacturers of 3D-printed parts are exploring ways to use the finishing method regardless of the challenges of doing so. There are strategies to create a successful and less complicated process.

Porosity compounds this issue by introducing voids beneath the surface that act as pathways for moisture and contaminants. These micro-voids can originate from incomplete melting, gas entrapment during the print process or binder burnout in metal binder jet parts. When left untreated, they enable corrosion to propagate beneath the coating, eventually leading to blistering or delamination. As a result, surface finishing for AM metals demands specialized pretreatment and densification strategies to create a sound foundation for reliable, long-term powder coated performance.

One of the most powerful advantages of AM is the ability to design metal parts with internal cavities, conformal cooling channels and lattice structures that dramatically reduce weight without compromising strength. These geometries, however, introduce significant complexity when it comes to powder coating. Unlike flat or open surfaces, internal recesses limit the ability of electrostatically charged powder to reach and adhere to all areas. The behavior of powder in such confined or irregular spaces depends heavily on line-of-sight access, Faraday cage effects and airflow dynamics during application, making uniform coverage a persistent challenge.

When powder cannot penetrate or charge evenly inside internal cavities or lattice structures, film thickness becomes highly variable. Thin or uncoated regions within recesses and cavities create potential weak points for corrosion, oxidation or thermal fatigue over time. These areas often go unnoticed until the part is in service, leading to premature coating failure. To mitigate this, coaters might experiment with modified spray techniques, auxiliary charging electrodes or fluidized bed coating methods to improve coverage, though none are universal solutions for every AM geometry.

The issue extends further when considering complex external geometries common to AM designs. Traditional powder coating lines are engineered for conventional parts, flat panels, brackets or tubular frames where spray paths and film builds are predictable. By contrast, 3D printed parts often contain overhangs, undercuts, internal webs and organic curves that disrupt airflow and electrostatic field uniformity. Ensuring full coverage without excessive build-up in these areas requires careful tuning of voltage, spray angle and powder feed rates.

Masking introduces another layer of complexity. Many AM parts feature functional surfaces such as precision bores, mating interfaces or threaded holes that must remain free of coating. Applying and removing masking materials on irregular or fine-featured parts is time consuming and may not be feasible for high-volume production. In some cases, manufacturers resort to post-coat machining to restore tolerances, though this adds cost and can compromise coating integrity near the cut edges.

Complicating all of this is the metallurgical variability inherent in AM materials. Unlike wrought metals, 3D printed alloys often exhibit non-equilibrium microstructures, residual stresses and surface oxides that vary with printing parameters and post-processing. These differences directly influence how pretreatments, such as acid etching, phosphating or chromating, react with the surface. For example, titanium and stainless steel AM parts often develop passive oxide layers that resist standard pretreatment chemistries, requiring customized formulations to ensure adhesion. Understanding and controlling these metallurgical nuances is critical to achieving a durable, uniform and high-quality powder-coated finish on AM components.

Preparing the surface of an AM metal part for powder coating requires a more comprehensive and deliberate approach than conventional finishing. The goal is to remove surface irregularities, eliminate contaminants and establish a consistent substrate that promotes strong adhesion and prevents coating defects. Because AM parts often emerge from the build chamber with loose powder, sintered particles and rough textures, mechanical and chemical surface-preparation strategies are typically used in combination to achieve optimal coating performance.

Mechanical finishing is the first and most direct method for improving surface uniformity. Techniques such as abrasive blasting using grit or glass bead media are highly effective for removing partially sintered powder and establishing a uniform anchor profile that promotes coating adhesion. Shot peening or tumbling may be used for batch processing of smaller components, smoothing surfaces and relieving internal stresses, though these methods are often less effective at reaching deep cavities or intricate lattice structures. For parts that contain precision mating surfaces or tight tolerances, machining or grinding may be employed to achieve the necessary dimensional accuracy. Together, these mechanical treatments not only enhance aesthetics but also significantly reduce the likelihood of outgassing during powder curing by eliminating loosely bound material and surface voids.

Following mechanical preparation and prior to powder coating, chemical pretreatment is essential for removing remaining oxides, residues or micro-contaminants that could interfere with bonding. Acid etching dissolves surface oxides and opens microscopic pores to promote coating grip.

Following mechanical preparation, chemical pretreatment is essential for developing corrosion resistance and ensuring proper adhesion of the powder coating. The chemical phase removes any remaining oxides, residues or micro-contaminants that could interfere with bonding. Acid etching is often the first step, effectively dissolving surface oxides and opening microscopic pores to promote coating grip. However, extra care must be taken with AM geometries to prevent acid entrapment in hidden cavities or lattice voids, which could cause later contamination or corrosion.

Once the surface is clean and chemically active, phosphate conversion coatings, typically based on iron, zinc or manganese, are commonly applied. These treatments form crystalline structures that create a stable, adherent foundation for the powder coating film. The phosphate layer also enhances corrosion resistance and improves coating uniformity across complex geometries. For parts intended for high-performance or aerospace applications, where traditional phosphates may not be compatible, chromate or non-chromate passivation systems are preferred.

Finally, aluminum and titanium AM alloys, which are increasingly used in aerospace and defense components, benefit greatly from such passivation treatments. These chemical processes form protective oxide layers that prevent galvanic corrosion while improving coating adhesion. When mechanical and chemical surface-preparation steps are applied in the correct sequence, the resulting substrate provides a smooth, dense and chemically balanced surface ideally suited for powder coating. This hybrid approach ensures that even the most complex 3D printed metal parts achieve the same durability, corrosion protection and aesthetic quality expected from conventional manufacturing.

Densification and Infiltration

As AM continues to evolve, densification and infiltration have become critical preparatory steps for ensuring reliable and high-quality powder coating performance. AM parts often contain interconnected pores and voids that can lead to outgassing, coating defects or corrosion initiation. By densifying the surface and internal structure before applying powder, manufacturers can dramatically improve coating adhesion, uniformity and long-term durability. This approach not only enhances the appearance of the final part but also transforms porous AM substrates into stable, finish-ready components.

One of the most effective densification methods is Hot Isostatic Pressing (HIP), a process that applies high temperature and uniform gas pressure to the part to collapse internal voids and increase density. HIP effectively removes porosity, improves mechanical strength and minimizes the risk of gas release during the powder curing process. Another strategy involves infiltration with resins or metallic alloys, which seals surface pores and smooths the substrate. Epoxy infiltration, for example, fills fine surface voids and creates a non-porous barrier layer that helps powder coatings distribute evenly and cure without defects. Metal infiltration using alloys compatible with the base material can also improve thermal and structural performance while reducing coating irregularities.

A third and increasingly popular approach is electroless plating, particularly with nickel or copper. These coatings deposit uniformly without the need for electrical current, even on complex or recessed geometries. Electroless nickel, especially mid- to high-phosphorus formulations, provides a dense, conductive and corrosion-resistant layer that seals porosity and enhances Faraday cage penetration during powder application.

By establishing a smooth and consistent surface, electroless plating effectively bridges the gap between rough, porous AM textures and the ideal substrate conditions required for high-quality powder coating.