Aluminum for Marine

Boat Hulls and Marine Structures

5083-H116 and 5083-H321 aluminum are the international standards for marine structures requiring high strength and excellent seawater corrosion resistance. 5083 is specified for ship hulls, superstructures, offshore platforms and pressure vessels operating in marine environments. The alloy provides tensile strength ≥305 MPa while resisting stress-corrosion cracking and exfoliation corrosion in seawater.

H116 temper is strain-hardened specifically for marine applications with guaranteed resistance to exfoliation corrosion and stress-corrosion cracking. H321 temper has similar properties. 5083-H116 plate in 3 – 12 mm thickness is used for boat hulls, bulkheads and decks on commercial vessels, ferries, patrol boats and large yachts.

For recreational boats and smaller craft, 5052-H32 sheet offers a good balance of strength (215 MPa tensile), corrosion resistance and lower cost than 5083. 5052 is widely used for pleasure boat hulls, pontoons, jon boats and aluminum fishing boats in 1.5 – 5 mm thickness.

• Large vessel hulls: 5083-H116 plate 5 – 12 mm, welded construction
• Superstructures: 5083-H321 plate 3 – 8 mm, painted or unpainted
• Recreational boats: 5052-H32 sheet 1.5 – 5 mm, riveted or welded
• Pontoons: 5052-H32 2 – 3 mm, formed and welded tubes

Decks and Non-Slip Surfaces

Marine decks require non-slip surfaces for crew and passenger safety. Aluminum checkered plate (also called tread plate or diamond plate) provides excellent slip resistance. 5052-H32 or 5083-H116 checkered plate in 3 – 6 mm thickness is standard for boat decks, gangways, offshore platform walkways and ship stairs.

The raised pattern (typically 5-bar or diamond pattern) provides grip even when wet or oiled. 5083-H116 checkered plate is specified for commercial vessels and offshore applications where high strength and seawater corrosion resistance are required. 5052-H32 checkered plate suits recreational boats and light-duty marine applications.

Deck plating is typically welded to longitudinal and transverse stiffeners. Stiffeners are typically 6061-T6 or 6082-T6 extruded profiles, or fabricated from 5083-H111 bar stock. The welded deck structure carries foot traffic, equipment loads and wave impact forces.

• Commercial decks: 5083-H116 checkered plate 4 – 6 mm, 5-bar pattern
• Recreational decks: 5052-H32 checkered plate 3 – 5 mm, diamond pattern
• Walkways: 5083-H116 or 5052-H32 checkered, welded to stiffeners
• Offshore platforms: 5083-H116 checkered plate 6 – 10 mm, heavy-duty

Marine Fittings and Hardware

Marine hardware—cleats, chocks, handrails, ladders, davits and deck fittings—must resist seawater corrosion and maintain strength under load. 6061-T6 aluminum extrusions are widely used for marine fittings and structural components where moderate-to-high strength (≥260 MPa) and good corrosion resistance are required.

Common marine extrusions include 6061-T6 tubes and pipes for railings and davits, 6061-T6 angles and channels for frame structures, and custom-extruded profiles for hatch coamings, toe rails and rub rails. 6061-T6 can be welded using TIG or MIG, though the heat-affected zone will soften; design joints accordingly.

7075 aluminum is generally avoided in marine applications due to its susceptibility to stress-corrosion cracking in seawater. Most marine fittings and hardware use 6061-T6, 5083-H116, or cast marine-grade aluminum alloys instead.

• Railings: 6061-T6 round tubes Ø25 – Ø50 mm, welded or bolted
• Ladders: 6061-T6 tubes and angles, welded construction
• Handrails: 6061-T6 extrusions, anodized finish
• Heavy fittings: 5083-H116 or 6061-T6 plate, machined or fabricated

Marine Fuel and Water Tanks

Marine fuel tanks, fresh water tanks and ballast tanks are fabricated from welded aluminum sheet or plate. 5052-O or 5052-H32 aluminum is the standard material for marine tanks due to its excellent formability, weldability and corrosion resistance. Tank walls are typically 3 – 6 mm thick depending on capacity and pressure rating.

5052 aluminum is compatible with gasoline, diesel and fresh water. For long-term diesel storage, the tank interior may be coated with epoxy or polyurethane to prevent algae growth and tank corrosion (though aluminum itself does not rust). Tank fittings—fuel pickups, fill caps, vent fittings—are typically machined from 6061-T6 bar stock or cast from marine-grade aluminum alloys.

ABYC H-24 (American Boat and Yacht Council) specifies minimum wall thickness for integral aluminum fuel tanks: 0.090 inch (2.29 mm) for tanks up to 25 gallons. 5083-H116 plate is used for larger fuel and ballast tanks on commercial vessels where higher strength is required. All marine tanks are welded using TIG (GTAW) or MIG (GMAW) with ER5356 or ER5183 filler alloys, then pressure-tested before installation.

• Fuel tanks: 5052-O or 5052-H32 3 – 6 mm (≥ 2.29 mm per ABYC H-24), TIG or MIG welded
• Water tanks: 5052-H32 2 – 5 mm, welded and pressure-tested
• Large tanks: 5083-H116 plate 5 – 10 mm, baffled construction
• Tank fittings: 6061-T6 bar, machined threads and flanges

Marine Corrosion Resistance

5xxx series aluminum alloys (5052, 5083) offer excellent natural resistance to seawater corrosion due to their magnesium content and the formation of a protective oxide layer. However, galvanic corrosion can occur when aluminum contacts dissimilar metals (bronze, stainless steel, copper) in the presence of seawater. Proper design isolates aluminum from other metals using nylon or rubber gaskets and plastic fasteners, or applies barrier coatings at contact points.

Marine aluminum is often left unpainted (bare) to take advantage of its natural corrosion resistance. The aluminum surface oxidizes to a matte gray patina that protects the underlying metal. For aesthetic reasons, marine structures may be painted with epoxy primers and polyurethane topcoats. Anodizing (Type II or hard anodizing) provides additional corrosion and wear resistance for hardware and fittings. Copper-based antifouling paints must not be applied directly to aluminum; use a barrier coat.

5083-H116 and 5083-H321 tempers are specifically strain-hardened to resist exfoliation corrosion (layer-by-layer peeling corrosion) and stress-corrosion cracking in marine environments. These tempers are required by shipbuilding standards for critical structural members. 5083 alloy can become sensitized (susceptible to intergranular corrosion) if held above approximately 65 °C (150 °F) for extended periods; avoid prolonged elevated-temperature service.

• Best marine alloys: 5083-H116/H321, 5052-H32, 6061-T6
• Avoid galvanic contact: isolate aluminum from stainless, bronze, copper
• Finish options: bare (natural oxide), painted (epoxy/polyurethane), anodized
• Welding: ER5356 or ER5183 filler alloys for 5xxx series

Marine Aluminum in Southeast Asia, Middle East and Africa

Southeast Asia has extensive boat-building industries in Vietnam, Thailand, Malaysia and the Philippines. Aluminum fishing boats, ferries, patrol boats and recreational boats are built using 5083-H116 and 5052-H32 sheet. Vietnam and Thailand are major exporters of aluminum boats to Australia, New Zealand and the Pacific islands.

The Middle East uses marine aluminum for offshore oil and gas platforms, fast patrol boats, landing craft and luxury yachts. UAE and Saudi Arabia import 5083-H116 plate, 6061-T6 profiles and marine-grade fittings. The region has high salinity and temperature, making corrosion resistance critical.

South Africa has commercial fishing and navy shipbuilding sectors using marine-grade aluminum. Nigeria imports 5083 and 5052 sheet for riverine patrol boats, ferries and offshore supply vessels serving the oil industry. Marine aluminum is preferred over steel for fast boats operating in tropical waters where corrosion maintenance is expensive.