3105
Al-Mn-Mg alloy with good formability and paint adhesion. A cost-effective choice for standard 25 mm blinds, roller-shutter skins and wide insect-screen or awning strip.
Shutter and blind strip guide
Aluminium Strip and Foil for Shutters and Blinds
Blind and shutter slats are roll-formed from thin, very hard aluminium strip, usually 3104, 3105, 5052 or 5182 in H19 or H48 temper, 0.12 to 0.50 mm thick and coil coated before forming. The alloy and temper decide how stiff the slat is and whether it springs back flat after being bent; the coating decides how it looks after years of sun. This guide explains how to choose and specify the strip for slat lines.
- Alloys
- 3104 · 3105 · 5052 · 5182
- Tempers
- H19 (bare) · H48 (coated)
- Thickness
- 0.12 – 0.50 mm
- Width
- 12.5 – 1250 mm slit coil
What the strip has to do in a blind or shutter
A venetian blind slat is a strip only a few hundredths of a millimetre thick that must stay straight across a wide window, tilt thousands of times and recover its curve after someone presses on it. A roller shutter slat is thicker and is rolled into a profile, often foam-filled, that must resist wind load and repeated coiling around the shaft. Both start as narrow coils of hard-rolled, pre-painted aluminium strip.
Aluminium wins this application because it is light enough for small motors and spring mechanisms, does not rust when the paint is scratched, and is non-combustible. The key engineering property is not tensile strength on its own but a high yield-to-thickness ratio: the strip must be hard enough that the slat does not take a permanent kink, yet still roll-form to a crown without cracking at the edges.
That is why slat strip is ordered in the fully hard H19 temper or in H48, which is strip rolled to full hardness and then given a light stabilising treatment during the paint bake. The magnesium-bearing 5052 and 5182 alloys give the highest spring-back for long, thin slats; the manganese alloys 3104 and 3105 are lower cost and are widely used for standard-width blinds and roller-shutter skins.
Alloys used for shutter and blind strip
Composition limits below are the registered Aluminum Association values (also used in EN 573-3). Single figures are maxima. Every Metline coil is supplied with a certificate stating the actual analysis.
| Element (wt %) | 3104 | 3105 | 5052 | 5182 |
|---|---|---|---|---|
| Silicon (Si) | 0.60 | 0.60 | 0.25 | 0.20 |
| Iron (Fe) | 0.80 | 0.70 | 0.40 | 0.35 |
| Copper (Cu) | 0.05 – 0.25 | 0.30 | 0.10 | 0.15 |
| Manganese (Mn) | 0.8 – 1.4 | 0.30 – 0.8 | 0.10 | 0.20 – 0.50 |
| Magnesium (Mg) | 0.8 – 1.3 | 0.20 – 0.8 | 2.2 – 2.8 | 4.0 – 5.0 |
| Chromium (Cr) | — | 0.20 | 0.15 – 0.35 | 0.10 |
| Zinc (Zn) | 0.25 | 0.40 | 0.10 | 0.25 |
| Titanium (Ti) | 0.10 | 0.10 | — | 0.10 |
| Gallium / Vanadium | 0.05 / 0.05 | — | — | — |
| Aluminium | Remainder | Remainder | Remainder | Remainder |
3104
Higher Mn and Mg than 3105, so it work-hardens to a stiffer slat. Familiar from beverage can bodies; used where 3105 is slightly too soft for the slat span.
5052
Al-Mg alloy with clearly higher strength and very good corrosion resistance. Common for premium 16 – 25 mm venetian slats and coastal installations.
5182
The strongest of the four (about 4.5 % Mg). Used for very thin, long slats that must recover after flexing, and for wide external blinds.
Strength ranges for H19 and H48 slat strip
Shutter strip is bought to a tensile-strength band rather than a minimum alone, because a slat that is too hard cracks during crowning and one that is too soft kinks in service. The bands below are typical order ranges used in blind-strip supply specifications (for example China's YS/T 621 for blind strip); confirm the agreed band on your order and on the mill certificate.
| Alloy | Temper | Thickness (mm) | Tensile strength (MPa) | Elongation (%) |
|---|---|---|---|---|
| 3104 / 3105 / 5052 | H19 | 0.12 – 0.18 | 300 – 370 | ≥ 1 |
| 3104 / 3105 / 5052 | H19 | 0.18 – 0.50 | 290 – 350 | ≥ 1 |
| 5182 | H19 | 0.12 – 0.50 | 360 – 440 | ≥ 1 |
| 3104 / 3105 / 5052 | H48 | 0.12 – 0.50 | 240 – 340 | ≥ 2 |
| 5182 | H48 | 0.12 – 0.50 | 300 – 400 | ≥ 2 |
H48 values are lower than H19 because the paint-curing oven (typically 220 – 260 °C peak metal temperature) partially recovers the cold-worked structure. Specify the temper you will receive after coating, not the temper of the bare coil.
Dimensions, tolerances and flatness
Typical supply range
- Thickness
- 0.12 – 0.50 mm (blind slats commonly 0.18 – 0.23 mm; shutter skins 0.25 – 0.45 mm)
- Width
- Narrow slit coil 12.5 – 100 mm; master coil over 100 up to 1250 mm
- Inner diameter
- 300 or 400 mm for narrow coil; 400 or 500 mm for wide coil; small 30 – 50 mm cores for coated ribbon pancakes
- Coil length
- Long, joint-free lengths to minimise line stops; agree a minimum metres per coil
- Surface
- Bare mill finish, coil coated (polyester, high-durability polyester, PVDF), printed wood-grain or anodised
| Width (mm) | Width tolerance (mm) | Thickness (mm) | Thickness tolerance (mm) |
|---|---|---|---|
| 12.5 – 50 | ± 0.05 | 0.12 – 0.18 | ± 0.003 |
| 50 – 100 | ± 0.10 | 0.18 – 0.25 | ± 0.005 |
| 100 – 1250 | ± 1.0 | 0.25 – 0.50 | ± 0.007 |
These are tight tolerances by general sheet standards (EN 485-4 or ANSI H35.2 allow more), so they must be written on the order. Flatness and camber matter just as much: narrow slit strip should show low wave height and minimal edge camber over a 2 m length, or the slats will not stack straight in the head rail. Burr height on slit edges should be kept low enough that it does not mark the paint or the forming rolls.
Coil coating and the tests that matter
Almost all slat strip is coated on a continuous coil line before slitting: pre-treatment, primer, then a top coat of 10 – 25 µm cured in an oven. Acrylic and polyester systems are standard for interior blinds; high-durability polyester or PVDF is chosen for external venetian blinds and roller shutters facing UV and coastal air.
| Property | Typical requirement | Common test method |
|---|---|---|
| Dry film thickness | Agreed value ± 1.5 µm | EN 13523-1 |
| Pencil hardness | ≥ 2H (acrylic), ≥ 3H (polyester) | EN 13523-4 / ASTM D3363 |
| Adhesion (cross-cut) | Grade 0, no detachment | EN 13523-6 / ISO 2409 |
| Solvent resistance | ≥ 10 MEK double rubs (more for PVDF) | EN 13523-11 / ASTM D5402 |
| Colour difference | No visible difference between coils; ΔE limit agreed | EN 13523-3 |
| Flexibility | No cracking on T-bend at the agreed rating | EN 13523-7 |
Ask for both faces to be specified: the visible face carries the decorative coat, while the reverse usually has a thinner backer. For printed wood-grain or dual-colour slats, confirm whether the print is a transfer film or an ink layer, because that changes scratch and UV performance.
Surface defects to reject
- Metal surface: cracks, corrosion spots, blisters, folds, roll marks, scratches, inclusions and indentations visible after coating
- Slit edges: cracked or wavy edges, burrs and edge deformation that disturb roll-forming or paint
- Coating: bubbles, orange peel, thick edges, craters, bare spots, colour streaks, particles and flow marks
- Winding: telescoping, loose wraps, interleaving damage and coil set that differs between coils
A short trial run on your own forming line is the most reliable acceptance test. Record the crown height and spring-back for the first coil of a new supply and use it as the reference for later lots.
How to choose alloy, temper and gauge
- Fix the slat geometrySlat width, crown and span decide the stiffness needed. Long spans and wide slats push you towards 5052 or 5182.
- Choose the environmentInterior blinds work well in 3105; external blinds near the sea benefit from 5052 or 5182 with a PVDF or HDP coating.
- Specify temper after coatingOrder H48 for coil-coated strip so the strength band reflects the baked condition.
- Set tolerances and coil dataThickness, width, camber, coil ID, OD limits and maximum joints per coil.
- Confirm testingMechanical tests per lot, coating tests per batch, and an EN 10204 3.1 certificate.
References and standards
- EN 13659 – Shutters and external venetian blinds: performance requirements including safety
- EN 1932 – External blinds and shutters: resistance to wind loads, test method
- EN 1396 – Aluminium and aluminium alloys: coil coated sheet and strip for general applications
- EN 13523 series – Coil coated metals: test methods
- The Aluminum Association – International Alloy Designations and Chemical Composition Limits
Shutter and blind aluminium strip: frequently asked questions
What is the difference between H19 and H48 strip?
H19 is extra-hard, cold-rolled strip as it leaves the mill. H48 is strip rolled to full hardness that has then been painted; the paint-curing heat lowers the strength slightly and stabilises it. Coated slat strip is therefore specified in H48.
Which alloy is best for venetian blind slats?
3105 suits standard interior blinds at the lowest cost. 5052 gives a stiffer, more corrosion-resistant slat, and 5182 gives the most spring-back for thin, long slats and external blinds.
What thickness is used for 25 mm blind slats?
Most 25 mm interior slats are about 0.18 – 0.21 mm thick. Wider slats and external blinds use thicker strip, and roller-shutter skins are typically 0.25 – 0.45 mm before roll-forming.
Can the strip be supplied slit to slat width?
Yes. Strip can be supplied slit to the exact width of your forming line, down to about 12.5 mm, with width tolerances as tight as ± 0.05 mm on narrow coil.
Is aluminum blind strip suitable for coastal buildings?
Yes, if the alloy and coating are chosen for it. 5xxx alloys with high-durability polyester or PVDF coatings resist salt air well; cut slat ends should be kept away from standing water.
Does Metline make finished blinds or shutters?
No. Metline supplies the aluminium strip and coil that slat manufacturers roll-form; the blinds and shutters themselves are made and installed by system companies.
Need strip for your slat line?
Tell us the alloy, temper, gauge, slit width, colour and coil size. We will confirm tolerances, coating tests and a delivered price.
