The aerospace sector relies on rigorous surface engineering to stop corrosion in airframes, engines, and interiors that face moisture, de-icing fluids, hydraulic oils, and salt-laden air. This guide explains the Top 10 Aerospace Corrosion Protection and Surface Treatment Processes in a structured, easy to follow way for learners at all levels. You will see how each process prepares, protects, and preserves metals and composites while supporting fatigue life, bond strength, and paint adhesion. Each section highlights what the process does, where it is used, and important control points to assure quality, compliance, and repeatable performance across new build and maintenance operations.
#1 Chromate Conversion Coating on Aluminum
Chromate conversion coating creates a thin, adherent oxide-chromate layer that passivates aluminum alloys and provides excellent paint adhesion. It is widely used on machined parts, sheet metal, and electrical bonding surfaces because the coating remains conductive at low thickness. Modern shops increasingly favor trivalent chromium processes as a safer, regulatory friendly alternative to legacy hexavalent systems while preserving adhesion and filiform corrosion resistance. Key controls include clean, active metal, tight immersion times, and thorough rinsing to avoid powdery films. After treatment, parts are typically primed quickly to lock in protection and prevent handling damage before assembly or storage.
#2 Sulfuric Acid Anodizing with Robust Sealing
Sulfuric acid anodizing grows a controlled porous oxide on aluminum that dramatically improves corrosion resistance and paint anchorage. The porous structure accepts dyes or corrosion inhibitors, then is sealed to close pores and reduce pathways for electrolytes. Sealing choices include hot deionized water, nickel acetate, or advanced low temperature seals that cut energy while maintaining performance. Thickness and uniformity must match alloy and geometry to avoid over-etching thin edges. Proper racking promotes even current distribution. After sealing, careful handling prevents scuffing of the hydrated oxide. Priming within process windows helps achieve durable systems in service and overhaul cycles.
#3 Boric-Sulfuric and Thin Film Sulfuric Anodizing
Boric-sulfuric acid anodizing and thin film sulfuric variants were developed to replace chromic acid anodizing while retaining its excellent fatigue and adhesion characteristics. These processes form thinner oxides that minimize crack initiation around fastener holes and edges, which is valuable for flight critical structures. They are widely specified for bonding pre-treatments where adhesive durability is essential. Process success depends on consistent bath chemistry, temperature, and cathode design to avoid burning. Post-anodize sealing is tuned to the intended topcoat or adhesive. Robust process controls, periodic coupons, and adhesion testing confirm the system supports long term corrosion resistance and structural reliability.
#4 Hardcoat Anodizing for Wear and Corrosion
Hardcoat anodizing creates a thicker, denser aluminum oxide for components that require both wear and corrosion performance, such as actuators, sliding tracks, and landing gear accessories. The higher thickness offers barrier protection and reduces fretting damage that can expose bare metal. To avoid embrittlement of delicate parts, thickness and microhardness must be matched to alloy and service environment. Sealing hardcoat can improve corrosion resistance, though some applications leave it unsealed to preserve dimensional control. Attention to edge buildup, masking, and dimensional allowances is critical, as is verifying coating integrity in bores and threads through microsectioning or eddy current checks.
#5 Stainless Steel Passivation with Nitric or Citric Chemistry
Passivation removes free iron and contaminants from stainless steel, promoting a chromium rich passive layer that resists pitting and crevice attack. Modern aerospace facilities favor citric based chemistries for safer handling while meeting stringent performance tests. Success begins with complete precleaning to remove machining oils and embedded particles that can seed rust. Time, temperature, and concentration are maintained to avoid etching delicate features. After treatment, high purity rinsing and controlled drying prevent water spots. Routine copper sulfate or salt spray tests help validate the passive state. Passivation is a finishing step, not a substitute for proper alloy selection and design.
#6 Cadmium Plating and Cadmium-Free Alternatives
Cadmium plating historically protected high strength steel fasteners and landing gear components due to its sacrificial behavior and lubricity. Environmental and health concerns drive strong movement toward cadmium-free systems. Zinc-nickel plating, ion vapor deposited aluminum, and aluminum inorganic coatings provide comparable galvanic protection with better sustainability. Choice depends on substrate, temperature limits, and electrical needs. Thorough hydrogen embrittlement relief baking is mandatory for high strength steels after any electroplating step. Torque-tension properties, thread fit, and paint compatibility must be verified. Transition plans typically pair rigorous qualification testing with field monitoring to ensure durability and maintainability match legacy performance.
#7 Phosphate Coatings and Organic Primers on Steel
Phosphate treatments, often zinc or manganese based, create microcrystalline layers that improve paint adhesion and provide initial corrosion resistance on carbon and low alloy steels. In aerospace, these coatings are commonly used under epoxy primers in non flight critical structures, ground equipment, and cabin hardware. Effective systems start with clean, activated surfaces and maintain bath accelerators within specification. After phosphating, rapid drying and priming prevent flash rust. Epoxy primers with active corrosion inhibitors, including non chromate technologies, provide long term protection and compatibility with polyurethane topcoats. Verification includes adhesion testing, humidity resistance, and cyclic corrosion exposure to simulate service.
#8 High Velocity Thermal Spray Metallic Barriers
Thermal spray processes, such as high velocity oxygen fuel and cold spray, apply dense aluminum or nickel-based metallic layers that act as robust barriers and sacrificial anodes on steels and certain alloys. They are valuable for landing gear, actuating systems, and repair of worn surfaces where plating limits or geometry challenges exist. Success requires meticulous grit blasting, masking, and surface cleanliness to achieve mechanical interlock. Spray parameters control porosity and oxide content that influence corrosion and fatigue behavior. Post-treatments can include sealing, grinding, and topcoating. Compared with plating, thermal spray offers local repair flexibility and reduced bath related risks.
#9 Epoxy Primers, Polyurethane Topcoats, and CIC Maintenance
Organic coating systems remain the frontline defense over conversion coatings, anodize, and plated layers. Two component epoxy primers deliver adhesion and inhibitor protection, while polyurethane topcoats add ultraviolet stability, chemical resistance, and color retention. Complex structures gain added life from periodic application of corrosion inhibiting compounds that creep into lap joints and faying surfaces to stop filiform and crevice attack. Best practice includes controlled film builds, environmental monitoring during spray, and cure verification. In service, wash cycles, touchups, and CIC reapplication are scheduled by zone and exposure. Coating health is tracked through inspections, thickness checks, and defect mapping.
#10 Cleanliness, Surface Activation, and Quality Control Foundations
Every protection scheme depends on clean, chemically active surfaces prepared by alkaline cleaning, solvent wiping, or aqueous degreasing, followed by deoxidizing or light abrasive treatments to remove oxides and smuts. Precision masking prevents overprocessing of bores and sealing surfaces. Process control plans define bath analyses, electrical parameters, and calibration. Representative test panels accompany production lots for salt fog, filiform, or wedge crack testing where required. Documentation ties each step to traceable results. Training, tooling design, and environmental controls prevent rework that can thin coatings or trap contaminants. This foundation turns good materials into durable systems that survive demanding service.