Hexagonal core
The standard geometry with the most predictable properties. Suits flat or gently curved panels such as floors, bulkheads and equipment decks.
Honeycomb core guide
5056 Aluminium Honeycomb Core
5056 aluminium honeycomb core is the highest-strength standard aluminium core: expanded from 5% magnesium foil, it carries roughly 15 – 25 % more compression and shear than 5052 core of the same density and resists salt spray better. It is the usual choice for aerospace sandwich panels, naval interiors and energy-absorbing parts. Metline supplies 5056 core in a wide range of cell sizes, densities and forms, unexpanded, expanded or cut to drawing, to customers worldwide.
- Foil alloy
- 5056 (Al-Mg 5)
- Cell size
- 1/16 – 3/4 in (1.6 – 19 mm)
- Density
- about 2 – 12 lb/ft³ (32 – 192 kg/m³)
- Specification
- AMS-C-7438
What is 5056 honeycomb core?
Honeycomb core is the lightweight middle layer of a sandwich panel. Two thin skins carry bending loads as tension and compression, while the core keeps them apart and carries shear between them. Doubling core thickness roughly quadruples stiffness for a very small weight increase, which is why honeycomb panels are found wherever stiffness per kilogram matters.
5056 core is made from 5056 aluminium foil, an alloy with 4.5 – 5.6 % magnesium. The foil is supplied in a fully hard condition, typically 5056-H39, to give the cell walls maximum strength. Compared with core made from 5052 foil (2.5 % Mg) or 3003 foil, 5056 core offers the highest compression and shear strength of the commercial aluminium cores and noticeably better resistance to salt spray and humid tropical air.
The trade-off is cost and formability. 5056 foil is harder to roll thin and the finished core is slightly less forgiving to form over tight curves, so designers use it where the extra strength or corrosion margin is needed, and choose 5052 or 3003 core for less demanding panels.
How 5056 honeycomb core is produced
- Foil preparationThin 5056 foil, commonly 0.0007 – 0.004 in (about 18 – 100 µm), is cleaned and given a corrosion-protective treatment such as phosphoric acid anodising or a conversion coating.
- Node linesParallel lines of adhesive are printed on the foil. Their spacing sets the cell size.
- Stacking and curingSheets are stacked with the adhesive lines offset by half a pitch and cured under heat and pressure to form a solid block (the unexpanded "HOBE" block).
- SlicingThe block is sliced to the core thickness (T direction) required.
- ExpansionEach slice is pulled open in the W direction, forming hexagonal cells. Over-expanding gives rectangular OX cells for easier curving.
- FinishingThe expanded core is trimmed, inspected for cell size and density and cut or machined to drawing.
High-density cores made from thick foil can also be produced by corrugating each sheet before bonding, which avoids the very high force needed to expand thick foil. Either way, the result has three principal directions: L (the ribbon direction, along the continuous foil), W (the expansion direction) and T (the thickness). Shear strength in L is typically about 1.5 – 1.8 times that in W, so panels should be laid out with the L direction along the main shear load.
Typical mechanical properties of 5056 core
Core strength rises steeply with density, which depends on foil gauge and cell size. The ranges below are indicative typical values compiled from published manufacturers' data for 5056 hexagonal core at room temperature. Specification minimums, for example those in AMS-C-7438, can be up to about 25 % lower, so design allowables must come from the specification or the certified lot data.
| Cell size | Density | Stabilised compression | Plate shear, L | Plate shear, W |
|---|---|---|---|---|
| 1/8 in (3.2 mm) | 3.1 lb/ft³ (50 kg/m³) | 2.0 – 2.4 MPa (290 – 350 psi) | 1.4 – 1.8 MPa | 0.9 – 1.0 MPa |
| 1/8 in (3.2 mm) | 4.5 – 4.8 lb/ft³ (72 – 77 kg/m³) | 4.3 – 4.8 MPa (620 – 700 psi) | 2.6 – 3.1 MPa | 1.6 – 2.2 MPa |
| 1/8 in (3.2 mm) | 6.1 lb/ft³ (98 kg/m³) | 6.7 – 7.3 MPa (970 – 1060 psi) | 3.6 – 4.1 MPa | 2.1 – 2.4 MPa |
| 3/16 in (4.8 mm) | 3.1 lb/ft³ (50 kg/m³) | 2.0 – 2.8 MPa | 1.5 – 2.1 MPa | 0.9 – 1.1 MPa |
| 3/16 in (4.8 mm) | 5.7 lb/ft³ (91 kg/m³) | 5.5 – 6.0 MPa | 3.4 – 3.8 MPa | 2.0 – 2.2 MPa |
Stabilised compression is measured with skins bonded to the core (ASTM C365); bare compression is lower. Shear is measured by the plate shear method (ASTM C273). Values vary between manufacturers and lots.
Other characteristics
- Foil alloy and temper
- 5056, typically H39 (full hard)
- Foil gauge
- about 0.0007 – 0.004 in (18 – 100 µm)
- Service temperature
- Up to about 175 °C (350 °F) with suitable node adhesive; check the adhesive rating
- Crush behaviour
- Steady plateau after initial peak; pre-crushing removes the peak for energy absorbers
- Electrical
- Conductive; useful for EMI shielding and grounding, but needs isolation from carbon-fibre skins
- Fire
- Non-combustible metal; the node adhesive and bonding film govern smoke and toxicity results
5056 honeycomb core configurations
Beyond plain hexagonal core, 5056 foil can be formed into several cell geometries and part forms. Match the type to the panel shape and load direction.
Over-expanded (OX) core
Cells pulled into an elongated, near-rectangular shape. Curves easily in the W direction, with higher W shear and lower L shear than hexagonal core.
Flexible core
A special cell shape that bends to tight radii and compound curves without anticlastic distortion, for fairings, ducts and leading edges.
Reinforced core
Extra foil bonded along the ribbons (double-wall or bonded strips) to raise local strength for hard points, insert zones and heavy loads.
Micro-cell core
Very small cells (1/16 in class) support thin skins and prevent dimpling, giving a smooth surface for precision panels and mirrors.
Perforated core
Small holes in the cell walls let air escape during bonding and allow venting or pressure equalisation in service.
Pre-crushed core
Core compressed slightly in the T direction to remove the initial strength peak, giving a flat crush curve for energy absorbers.
Block and machined core
Thick expanded blocks milled to contour, chamfered or pocketed to drawing, ready for bonding.
Preformed core
Core heat-formed or shaped to a specific curvature before lay-up, used for cabin walls, radomes and shells.
Surface treatments and corrosion protection
Honeycomb panels fail far more often from corrosion at the bond line than from overload, so foil treatment matters. 5056 already resists corrosion better than 5052, but aerospace and marine panels normally add one of these treatments:
Phosphoric acid anodising
Creates a porous oxide that adhesives key into strongly and that resists moisture. The usual treatment for structural aerospace core, often followed by a corrosion-inhibiting primer.
Conversion coating
Chromate or chromium-free conversion coatings give good corrosion protection and paint adhesion at lower cost for industrial and marine panels.
Primer and coatings
Corrosion-inhibiting primer applied over anodised or converted foil, for panels in wet or salt-laden service.
Also design out moisture paths: seal panel edges, use potted inserts, and add a glass-fibre isolation ply between aluminium core and carbon-fibre skins to prevent galvanic corrosion.
Sizes, tolerances and supply condition
| Parameter | Typical standard | Maximum / option | Tolerance |
|---|---|---|---|
| Ribbon length (L) | 1220 mm (48 in) | up to about 2540 mm (100 in) | +50 / −0 mm |
| Width (W, expanded) | 2440 mm (96 in) | up to about 3660 mm (144 in) | +100 / −0 mm |
| Common sheet sizes | 1220 × 2440, 1220 × 3050, 1220 × 3660, 1524 × 3050 mm | cut to size | — |
| Thickness (T) | any slice thickness | blocks to several hundred mm | ±0.13 mm up to 102 mm; about ±1.6 mm above |
| Density | per specification | — | ±10 % |
| Cell size | per specification | — | ±10 % |
- Unexpanded block or slices: lowest freight volume; you expand the core on site
- Expanded sheets: ready for lay-up and bonding
- Cut kits and machined parts: cut to drawing, chamfered or contoured, packed by panel
- Finished panels: bonded sandwich panels with aluminium, glass-fibre or carbon skins on request
Orders follow the industry naming convention cell size – alloy – foil gauge – density, for example 1/8-5056-.001 (3.1 pcf), plus the treatment, perforation and whether the core is expanded. Giving all of these avoids ambiguity between suppliers.
Where 5056 honeycomb core is used
| Sector | Typical parts | Why 5056 core |
|---|---|---|
| Aerospace | Flooring, flap and spoiler cores, fairings, equipment shelves, satellite panels | Highest strength-to-weight of aluminium cores; anodised and qualified to AMS-C-7438 |
| Marine and offshore | Bulkheads, interior partitions, deck equipment platforms, enclosures | Better salt-spray resistance than 5052 or 3003 core |
| Defence | Shelters, transit cases, blast and impact layers, missile structures | High crush strength and energy absorption |
| Rail and transport | Floors, ceilings, doors and equipment boxes | Stiff, light and dimensionally stable |
| Energy absorption | Crash pads, impact attenuators, test barriers | Predictable crush plateau, especially when pre-crushed |
| Industrial | Machine tables, clean-room panels, air-flow straighteners | Flat, rigid and easy to machine |
5056 compared with 5052 and 3003 core
| Property | 5056 core | 5052 core | 3003 core |
|---|---|---|---|
| Foil magnesium | 4.5 – 5.6 % | 2.2 – 2.8 % | none (Mn alloy) |
| Relative strength at equal density | Highest (about 15 – 25 % above 5052) | Baseline | Lowest |
| Salt-spray resistance | Very good | Good | Fair |
| Formability over curves | Good | Very good | Very good |
| Typical market | Aerospace, marine, defence | Aerospace, transport, general | Architecture, signage, industrial |
| Relative cost | Highest | Medium | Lowest |
If weight is critical and loads are moderate, 5052 core of slightly higher density may match a lighter 5056 core at lower cost; compare on strength per kilogram, not grade alone. Non-metallic aramid core is the alternative where electrical insulation, low thermal conductivity or very tight curvature matter more than strength.
How to specify 5056 honeycomb core
- Define the loadsCalculate the core shear stress and flatwise compression from panel span, load and skin thickness, with a safety factor.
- Pick densityChoose the lightest density whose minimum shear and compression (not typical values) exceed the design stresses.
- Pick cell sizeSmaller cells support thin skins and prevent dimpling; larger cells reduce cost at the same density.
- Orient the corePut the L direction along the higher shear load; specify OX or flexible core for curved panels.
- Specify treatment and testsAnodising or coating, perforation, and the test standard (AMS-C-7438, ASTM C273, C365, C297).
References and standards
- SAE AMS-C-7438 – Core Material, Aluminum, for Sandwich Construction
- ASTM C273 – Shear Properties of Sandwich Core Materials
- ASTM C365 – Flatwise Compressive Properties of Sandwich Cores
- ASTM C297 – Flatwise Tensile Strength of Sandwich Constructions
- The Aluminum Association – International Alloy Designations and Chemical Composition Limits
5056 aluminium (aluminum) honeycomb core: FAQ
How much stronger is 5056 core than 5052 core?
At the same cell size and density, 5056 core is typically about 15 – 25 % stronger in compression and shear, because its foil contains roughly twice the magnesium. It also resists salt spray better.
What do the L, W and T directions mean?
L is the ribbon direction along the continuous foil, W is the direction in which the block was expanded, and T is the core thickness. Shear strength is highest in L, roughly 1.5 – 1.8 times that in W.
Can 5056 honeycomb core be curved?
Hexagonal core bends in one direction but forms a saddle shape over compound curves. For curved panels, order over-expanded (OX) core, flexible core or preformed core.
Which skins can be bonded to 5056 core?
Aluminium, titanium, stainless steel, glass-fibre and carbon-fibre skins are all used. With carbon-fibre skins add a glass-fibre isolation ply to avoid galvanic corrosion of the aluminium core.
Why buy unexpanded core?
Unexpanded blocks or slices take up a small fraction of the volume of expanded core, which cuts freight cost for large orders. You then expand the core in your own facility.
Which test reports can be supplied?
Density, cell size and thickness reports, plus compression and shear test results to ASTM C365 and C273 where specified, with lot traceability. Tell us the specification, for example AMS-C-7438, when you enquire.
Need 5056 honeycomb core?
Send the cell size, density, thickness, sheet size and quantity, or your panel drawing. We will reply with options, test documents and a delivered price.
