Small cells (3 mm)
Support thin skins without dimpling, give the best surface finish and the highest strength at a given foil. Heavier and more costly.
Honeycomb core guide
5A12 Aerospace Aluminium Honeycomb Core
5A12 honeycomb core is a hexagonal cell structure made from foil of 5A12, a high-magnesium (about 9 % Mg) aluminium alloy registered in Chinese standards. Bonded between two thin skins it forms a sandwich panel that is very stiff for its weight, and the high-magnesium foil gives more compressive and shear strength per unit density than ordinary 3003 or 5052 core. This guide explains the alloy, how to choose cell size, foil and density, which standards apply and when 5052 or 5056 is the better choice.
- Foil alloy
- 5A12 (formerly LF12)
- Magnesium
- about 8.3 – 9.6 %
- Density range
- about 27 – 140 kg/m³
- Forms
- Block, expanded slice, panels
What is 5A12 honeycomb core?
Aluminium honeycomb is made by printing lines of adhesive on stacked sheets of thin foil, curing the stack into a solid block, slicing the block to the required thickness and then pulling the slices open so the bonded and unbonded zones form hexagonal cells. The result is a core that is mostly air, yet when bonded between face sheets it keeps the skins apart and carries shear, much like the web of an I-beam.
The foil alloy sets the strength of every cell wall. 5A12, formerly LF12, is one of the most highly alloyed Al-Mg grades in the GB/T 3190 standard, with roughly twice the magnesium of 5056. In foil form it is strong and springy, so a 5A12 core reaches a given compressive or shear strength at lower density than 5052 core. That is why it is specified on Chinese aerospace and space programmes where weight is critical: satellite structural panels, equipment decks, launch-vehicle fairings and aircraft secondary structure.
Like other high-magnesium alloys, 5A12 is not used where the core will see sustained elevated temperatures in a corrosive setting, because it can sensitise. In practice aerospace sandwich panels are sealed, the foil is given a corrosion-resistant surface treatment and the panel is protected by its skins, but the service temperature should still be part of the selection.
5A12 foil chemical composition (wt %)
| Element | Limit |
|---|---|
| Magnesium (Mg) | 8.3 – 9.6 |
| Manganese (Mn) | 0.40 – 0.8 |
| Titanium (Ti) | 0.05 – 0.15 |
| Silicon (Si) | ≤ 0.30 |
| Iron (Fe) | ≤ 0.30 |
| Copper (Cu) | ≤ 0.05 |
| Zinc (Zn) | ≤ 0.20 |
| Nickel (Ni) | ≤ 0.10 |
| Beryllium, antimony | Small controlled additions |
| Aluminium (Al) | Remainder |
Main limits per GB/T 3190; the foil certificate states the actual analysis of each lot.
How cell size, foil thickness and density interact
Three numbers describe any honeycomb: the cell size (the distance across flats of a hexagon), the foil thickness and the resulting density. They are linked: for a given cell size, thicker foil means higher density; for a given foil, smaller cells mean higher density. Strength rises faster than density, roughly with density to the power 1.5, so a modest increase in density buys a large increase in strength.
The Chinese specification code reads as cell size, alloy and density. For example, 5-5A12-52 is a 5 mm cell in 5A12 foil at 52 kg/m³. The table shows common combinations with indicative stabilised flatwise compressive strength.
| Code | Cell size | Foil | Density (kg/m³) | Flatwise compression, indicative (MPa) |
|---|---|---|---|---|
| 3-5A12-66 | 3 mm | 0.03 mm | 66 | 2.75 |
| 3-5A12-77 | 3 mm | 0.04 mm | 77 | 3.57 |
| 5-5A12-44 | 5 mm | 0.03 mm | 44 | 1.36 |
| 5-5A12-52 | 5 mm | 0.04 mm | 52 | 1.84 |
| 5-5A12-68 | 5 mm | 0.05 mm | 68 | 2.88 |
| 5-5A12-81 | 5 mm | 0.06 mm | 81 | 3.85 |
| 5-5A12-110 | 5 mm | 0.08 mm | 110 | 6.29 |
| 7-5A12-39 | 7 mm | 0.04 mm | 39 | 1.13 |
| 7-5A12-53 | 7 mm | 0.05 mm | 53 | 1.90 |
| 7-5A12-84 | 7 mm | 0.08 mm | 84 | 4.11 |
| 8-5A12-41 | 8 mm | 0.05 mm | 41 | 1.23 |
| 8-5A12-67 | 8 mm | 0.08 mm | 67 | 2.82 |
Indicative values for comparison only. Design allowables must come from the governing specification and batch test results (for example compression tested to ASTM C365).
Medium cells (5 mm)
The general choice for aerospace panels, balancing skin support, strength and weight.
Large cells (7 – 8 mm)
Lowest density for lightly loaded panels and large flat areas; require thicker skins to avoid intra-cell buckling.
Strength directions and what to test
Honeycomb is anisotropic. The L direction runs along the ribbon (the direction of the continuous foil), and the W direction is the expansion direction. Because the double-thickness bonded walls run in L, shear strength and modulus in L are typically about 1.5 – 2 times those in W. Panels should be laid out with the L direction aligned to the main shear load.
| Property | Test method | Why it matters |
|---|---|---|
| Density | ASTM C271 | Primary acceptance check; confirms foil and cell geometry |
| Flatwise compression (bare and stabilised) | ASTM C365 | Resistance to crushing under point loads and handling |
| Plate shear, L and W | ASTM C273 | Governs panel bending stiffness and strength |
| Flatwise tension | ASTM C297 | Checks the skin-to-core bond |
| Node bond strength | Purchaser or core specification | Ensures cells do not separate during expansion and machining |
Standards for 5A12 and other aerospace cores
Relevant specifications
- HB 5443
- Chinese aviation industry standard for aluminium honeycomb core; the usual basis for 5A12 core
- SAE AMS-C-7438
- Aluminium core material for sandwich construction (successor to MIL-C-7438); covers 5052, 5056 and 2024 cores
- SAE AMS-A-81596
- Uncoated aluminium foil for honeycomb core
- ASTM C271, C273, C297, C365
- Test methods for sandwich core density, shear, flatwise tension and compression
An important practical point: AMS-C-7438 does not list 5A12. If a programme is qualified to AMS-C-7438, the equivalent high-strength choice is 5056 core; 5A12 is ordered to HB 5443 or to a purchaser specification that defines the alloy, geometry and acceptance tests.
5A12 compared with 5052 and 5056 honeycomb
| Point | 5052 core | 5056 core | 5A12 core |
|---|---|---|---|
| Foil magnesium | about 2.5 % | about 5 % | about 9 % |
| Strength at equal density | Baseline | Higher | Highest of the three |
| Standards | AMS-C-7438, widely qualified | AMS-C-7438, aerospace | HB 5443, Chinese programmes |
| Availability | Very wide | Wide | More specialised |
| Typical use | Aerospace and industrial panels, marine, rail | Higher-load aerospace panels | Weight-critical space and aircraft panels |
For most commercial sandwich panels 5052 honeycomb core is the default; 5056 core is the step up when an internationally recognised high-strength core is needed. Choose 5A12 when the drawing calls for it or the weight target cannot be met otherwise.
Supply forms and options
Unexpanded block
Bonded HOBE block for customers who slice and expand in-house; compact to ship.
Expanded slices
Cut to thickness and expanded to sheet size, ready for bonding. Thickness tolerance is agreed per order.
Perforated core
Small vent holes in the cell walls let air escape during autoclave or vacuum cure and equalise pressure in space vacuum.
Surface treatment
Foil treated for corrosion resistance and adhesive bonding.
Machined core
Contoured, chamfered or pocketed core for inserts and edge close-outs.
Finished panels
Sandwich panels with aluminium or composite skins can be arranged to drawing.
Where 5A12 honeycomb is used
- Spacecraft: satellite structural panels, equipment decks and solar-array substrates where stiffness, flatness and low mass matter
- Launch vehicles: fairing panels, interstage structures and crushable energy absorbers for landing loads
- Aircraft: floor panels, fairings, access doors, control-surface and nacelle sandwich parts
- Defence and marine: lightweight bulkheads, shelters and radar structures needing a metallic core
References and standards
- SAE AMS-C-7438 – Core Material, Aluminum, for Sandwich Construction
- SAE AMS-A-81596 – Aluminum Foil for Sandwich Construction
- ASTM C365 – Standard Test Method for Flatwise Compressive Properties of Sandwich Cores
- ASTM C273 – Standard Test Method for Shear Properties of Sandwich Core Materials
- GB/T 3190 – Chemical composition of wrought aluminium and aluminium alloys
- HB 5443 – Aluminium honeycomb core specification (Chinese aviation industry standard)
5A12 honeycomb core: frequently asked questions
What is 5A12 aluminium honeycomb made of?
Foil of 5A12, a high-magnesium Al-Mg alloy with about 8.3 – 9.6 % magnesium and some manganese, bonded into hexagonal cells.
Is 5A12 honeycomb stronger than 5052 aluminum honeycomb?
At equal density, yes: the higher-magnesium foil gives more compressive and shear strength. That lets designers reach a strength target with a lighter core.
Can 5A12 core be supplied to AMS-C-7438?
No. AMS-C-7438 covers 5052, 5056 and 2024 cores. 5A12 is normally supplied to HB 5443 or a purchaser specification; use 5056 if AMS-C-7438 compliance is required.
What do the codes like 5-5A12-52 mean?
The first number is the cell size in millimetres, then the alloy, then the nominal density in kg/m³. 5-5A12-52 is a 5 mm cell in 5A12 foil at about 52 kg/m³.
Which direction of honeycomb is stronger?
The L (ribbon) direction, where the double-thickness bonded walls run. Shear strength in L is typically about 1.5 – 2 times that in W.
Can the core be perforated?
Yes. Perforated core lets trapped air escape during cure and equalises pressure in vacuum, which is common for space hardware.
Need 5A12 honeycomb core?
Send cell size, density, thickness, sheet size and test requirements. Metline will confirm options, documentation and delivery.
