What 1235 Pure Aluminum Foil Is
1235 is a 1000-series wrought aluminium grade with a minimum aluminium content of 99.35%. In foil form it is registered as UNS A91235 and is normally supplied in the O (annealed) temper, the softest and most formable condition of the pure-aluminium family. The residual iron and silicon in the grade are deliberate: they pin grain growth during final annealing and keep very thin gauges from collapsing during rolling, slitting and unwinding.
Foil is produced either from continuous-cast stock or from direct-chill slabs that are hot rolled to strip and then cold rolled on tandem mills. Gauges below roughly 0.2 mm are made by foil rolling, in which two webs are rolled together and later separated, which leaves each web with one bright and one matte face.
Composition and Mechanical Behaviour
| Element | Limit, % | Role |
|---|---|---|
| Aluminium | 99.35 min | Base metal; sets conductivity, reflectivity and formability |
| Si + Fe | 0.65 max | Controls grain size and recrystallisation during anneal |
| Cu | 0.05 max | Impurity limit |
| Mn | 0.05 max | Impurity limit |
| Mg | 0.05 max | Impurity limit |
| Zn | 0.05 max | Impurity limit |
| Ti | 0.03 max | Impurity limit |
| Others, each | 0.03 max | Impurity limit |
Composition limits of this type are tabulated for 1235 in ASTM B209 and in GB/T 3190, and the two agree closely, so either can be quoted on a specification sheet. Because 1235 contains no intentional hardening elements, it cannot be strengthened by heat treatment. Properties are fixed instead by the cold reduction left in the web and by the final anneal. In the O temper the tensile strength of foil typically falls in the 60 to 100 MPa band, with elongation well above 20% at common gauges, which is what allows sharp wrapping around cable cores without through-thickness cracking.
Gauges, Widths and Coil Formats
| Parameter | Range or note |
|---|---|
| Thickness | 0.006 to 0.05 mm |
| Width | 90 to 1600 mm |
| Length | Continuous coil; cut lengths on request |
| Coil inner diameter | 76 mm or 152 mm |
| Temper | O as standard; H18 where higher stiffness is required |
| Gauge tolerance | Agreed against the foil rolling standard in force, such as GB/T 3198 |
Gauge tolerance is the first item to fix in an order. Double-rolled foil is measured as stacked thickness, so the acceptance window must state how the two plies are treated and at which points across the width the gauge is checked. Width tolerance and edge condition matter just as much on high-speed coating and slitting lines.
Where the Grade Is Used
Cable wrap. The foil forms an electrostatic shield and moisture barrier around conductors. The O temper lets it conform tightly to the core, and the soft surface bedded against insulation does not abrade it.
Adhesive tape. 1235 is lacquered or laminated, then coated with adhesive. Surface cleanliness governs adhesion, so rolling-oil residue has to be controlled before coating.
Battery current collectors. Surface condition, oil residue and gauge consistency matter more than strength, because contamination raises interfacial resistance at the electrode interface.
Heat exchange and lamination. Thin gauges are bonded to other substrates where high thermal conductivity, reflectivity and low weight are wanted.
Processing and Handling Notes
Slitting sets edge quality. Burrs and slivers from worn knives cause web breaks on downstream coating lines, and the usual control is to keep knife clearance proportional to gauge while holding unwind tension steady. For battery and capacitor work a low-dew-point anneal and clean packaging do more for performance than any small compositional change, since a fraction of a micrometre of oil can measurably increase contact resistance.
Because the foil is very soft, handling at gauges below 0.01 mm needs care: a crease is permanent and will print through a lacquer or laminate. Storage in a dry, plain atmosphere avoids the moisture staining that pure aluminium can develop after damp conditions, and coils should be supported on their full width rather than on edges.
Common Misconceptions
"1000 series means one alloy." 1050, 1060, 1070, 1100 and 1235 have different aluminium minima and impurity limits and are not interchangeable in every process.
"Pure foil cannot hold shape." The O temper is soft, but the H18 condition exists precisely for cases where stiffness is wanted.
"Rust-free means it never oxidises." A natural oxide forms within minutes in air; the advantage of the grade is a stable, self-limiting oxide instead of a flaking corrosion product.
"A thicker gauge is always stronger." Gauge raises load capacity but does not change temper, and a soft thick foil can still deform under light handling.
"Any foil will do for a current collector." Surface chemistry and residue determine behaviour long before alloy choice does.
FAQ
Q: What does the 1235 designation mean?
It identifies a 1000-series aluminium grade with a minimum aluminium content of 99.35%, registered internationally as UNS A91235.
Q: Why is 1235 usually supplied in the O temper?
Annealing to O gives the highest ductility and the most uniform surface, which is what wrapping, coating and bonding operations need.
Q: Can 1235 be heat treated to a stronger condition?
No. It contains no alloying elements that respond to precipitation hardening; strength is set only by cold reduction and annealing.
Q: What is the thinnest foil normally available?
Around 0.006 mm is the practical lower limit for double-rolled 1235, with 0.009 to 0.03 mm covering most cable, tape and battery orders.
Q: How should the surface be prepared before lacquering?
The foil should be free of rolling oil and dust, checked by a water-break or tape test, and handled with clean gloves to avoid fingerprints that show after coating.
Q: Does 1235 corrode outdoors?
It forms a protective oxide and performs well in normal atmospheres, but it is not intended for prolonged marine or heavily polluted exposure, where 5052 or 3003 is the better choice.