1100-O aluminum foil is the fully annealed, commercially pure grade used for capacitor shells and casings, where softness, conductivity and surface cleanliness decide whether the component performs reliably. With 99.00% minimum aluminium, the material draws and stamps into thin cylindrical and rectangular shells without splitting, and its uniform oxide behaviour supports both welded and crimped assembly. This guide explains what the annealed temper means, which properties matter in capacitor production, and the tolerances that should be agreed before an order is placed.
What Is 1100-O Capacitor Shell Aluminum Foil?
1100 is a 1xxx series wrought alloy in which aluminium is present at 99.00% minimum and silicon plus iron, at no more than 0.95% combined, are the only significant impurities. The suffix O denotes the annealed temper: the coil has been heated until the rolled structure recrystallises and then cooled under control, leaving it soft, ductile and essentially free from the residual stresses introduced by cold reduction.
Product listings occasionally write this condition as 1100-HO, but the correct designation for fully annealed material is 1100-O. The two must not be confused with H1x strain-hardened tempers, which are considerably stiffer and can crack when a shell is drawn deeply. Ordering by designation alone is not enough, because mechanical properties of thin annealed foil depend strongly on gauge and on the final annealing cycle, so tensile and elongation values should always be written into the specification.
Purity, Temper and Electrical Performance
Capacitor shells sit inside the electrical circuit of the finished component, so conductivity and chemical consistency are functional requirements rather than cosmetic ones. A high-purity matrix keeps resistivity low, gives predictable eddy-current and dielectric behaviour, and allows a thin, even surface oxide to form where the shell body is anodized or where a passive layer is needed. The annealed temper delivers the highest electrical conductivity available in this alloy, at approximately 61% IACS.
Aluminium: 99.00% minimum
Silicon plus iron: 0.95% maximum
Copper: 0.05-0.20%
Manganese: 0.05% maximum
Zinc: 0.10% maximum
Other elements: 0.05% each maximum, 0.15% total maximum
Because the grade is not heat treatable, no aging or solution treatment is involved. Strength comes only from cold work, so any additional rolling after the final anneal would harden the foil and reduce the drawability that capacitor shells depend on. Slitting, re-winding and handling are therefore carried out in a way that adds as little strain as possible.
Typical Specifications
| Property | Typical value |
|---|---|
| Alloy and temper | 1100-O, fully annealed |
| Purity | 99.00% aluminium minimum |
| Thickness | 0.02-0.30 mm, matched to shell width and draw depth |
| Width | Slit to order, up to 1250 mm |
| Coil inner diameter | 76 mm or 152 mm |
| Tensile strength | About 90 MPa in the annealed condition |
| Elongation | 30% and above on annealed stock |
| Electrical conductivity | Approximately 61% IACS |
| Thermal conductivity | 222 W/(m.K) |
| Density | 2.71 g/cm3 |
| Melting range | 643-657 degrees C |
| Surface | Smooth, bright, free from slivers, oil marks and folds |
Composition is controlled to GB/T 3190 and EN 573-3, foil is produced and tested to GB/T 3198, EN 546-1 and EN 546-2, and electrical behaviour is verified along the lines of ASTM B193. Shell strip rolled heavier than foil gauge is supplied to ASTM B209.
Manufacturing Route and Quality Control
Production starts with rolling to intermediate gauge, followed by process annealing and further cold reduction to the ordered thickness. The final full anneal sets the recrystallised grain structure and the mechanical properties, and slitting to customer width follows under controlled tension so that the coil does not pick up edge strain. Throughout the route the foil is handled on lined rolls to prevent surface damage.
Thickness gauged continuously across the full width, not only at the centre line
Surface inspected for slivers, pinholes, roll marks, oil residue and folds
Tensile strength and elongation tested on every production lot
Conductivity checked to confirm the purity level of the melt
Camber, coil set and winding tension controlled for trouble-free unwinding on automatic presses
Material is packed on export wooden pallets with craft paper and moisture protection, and coils are strapped and identified so that heat number, gauge and width can be traced back to the production record. Production orders are normally delivered in 25-35 days, with ready stock dispatched in 7-10 days.
Applications in Capacitor and Electronic Assembly
The soft temper and clean surface make the foil suitable for drawing, deep drawing, stamping and crimping. Typical uses include:
Shells and casings for aluminium electrolytic capacitors
Housings and covers for film and power capacitors
Cans and shielding sleeves for electronic components
Internal liners and wrapping for sensitive electrical parts
Light reflectors and heat spreading components in electronic assemblies
When the shell is welded, the low impurity level keeps the weld pool clean and reduces the risk of porosity, while the annealed structure accommodates the small amount of deformation that crimping and seaming require. Where the finished part is anodized, the fine recrystallised grain promotes an even oxide layer.
Frequently Asked Questions
Q: What does the O temper mean on 1100 capacitor foil?
O is the annealed temper. The coil is heat treated so that the grains recrystallise and internal stresses relax, which leaves the foil at its softest and most ductile condition and at its highest electrical conductivity.
Q: Is 1100-HO the same as 1100-O?
The fully annealed condition is correctly written as 1100-O. The form 1100-HO appears in some product listings but is not a standard temper designation, so orders and drawings should specify 1100-O together with the required tensile strength and elongation.
Q: What thickness is used for capacitor shells?
Shell stock is normally drawn from foil between 0.02 mm and 0.30 mm. The exact gauge follows the shell diameter, the draw depth and the mechanical strength the casing must provide, and it is best fixed from a formed sample.
Q: Why is high purity important for this application?
Purity above 99.00% keeps electrical resistivity low, produces a uniform surface oxide and allows the foil to be drawn very thin without tearing. Impurity phases would also act as initiation points for cracking during forming.
Q: Can 1100-O foil be welded or soldered?
Yes. Gas tungsten arc and resistance welding are both used for shells, and soldering and brazing work well on the clean annealed surface. The alloy is not heat treatable, so no post-weld aging treatment is required.
Q: How is the foil supplied and protected?
It is delivered in coils with a 76 mm or 152 mm inner diameter, slit to the required width and packed on export wooden pallets with craft paper and moisture protection. Gauge, width, temper and coil weight are all matched to the press line.
