Alloy Design of AA8079 Foil
AA8079 is a non-heat-treatable aluminium foil alloy of the Al-Fe-Si family. It is rolled to final gauge in O, H18, H22 and H24 tempers, most often between 0.006 mm and 0.20 mm. The alloy contains only trace copper and no deliberate magnesium addition, so it cannot be strengthened by precipitation hardening. Its forming behaviour comes instead from a fine dispersion of iron-bearing phases of the Al6Fe and Al3Fe type that is distributed through a recrystallised aluminium matrix.
A frequently repeated description of 8079 as an "8 % silicon, 0.9 % magnesium" alloy hardened by Mg2Si precipitates is incorrect; those figures belong to cast Al-Si alloys. The correct specification window is given below.
| Element | Content, % by mass | Role in the alloy |
|---|---|---|
| Si | 0.05-0.30 | refines the iron-bearing dispersoids |
| Fe | 0.70-1.30 | principal strengthening and grain-refining element |
| Cu | 0.05 max | kept low for chemical resistance |
| Mn | 0.05 max | balanced against iron |
| Mg | 0.05 max | no precipitation hardening route |
| Zn | 0.10 max | impurity control |
| Ti | 0.08 max | cast grain refinement |
| Al | balance | matrix |
Typical mechanical values for soft 8079-O foil are 100-130 MPa tensile strength with 15-25 % elongation at 50 mm gauge length; H18 foil reaches roughly 180-220 MPa with much lower elongation. Tension testing of foil of this gauge is carried out to ASTM E345. Dimensional and mechanical requirements for foil are specified in ASTM B479 and EN 546-2, with GB/T 3198 covering the same ground for the domestic market, and chemical composition is quoted to EN 573-3.
Why 8079 Foil Draws Well
Deep drawing of thin foil is governed by three factors: the strain hardening behaviour of the metal, the uniformity of thickness across the blank, and the friction between foil, punch and die. The alloy design of 8079 addresses all three.
Fine, evenly distributed Al-Fe-Si dispersoids pin the grain boundaries, so the recrystallised grain size stays small and uniform after the final cold reduction, which is normally above 90 %.
A weakly anisotropic texture keeps earing low, so a drawn cup holds a level rim instead of growing four ears that have to be trimmed away.
Iron in solid solution and as dispersoid raises the strain hardening exponent without pushing the metal toward brittle fracture, allowing the wall to thin progressively instead of failing abruptly.
Tight gauge tolerances keep the metal flow balanced between the flange and the wall of the cup.
Wall thinning is limited by the local strain the foil can accept. With 15-25 % elongation in the soft temper, cups deeper than about one diameter are normally produced in several stages, with an interanneal between the heavier reductions.
Friction, Lubrication and Tooling Practice
Aluminium foil carries a natural oxide film only 2-4 nm thick. This film is hard and chemically bonded to the metal, so it contributes boundary lubrication during first contact but also acts as a mild abrasive if it is broken up dry. Practical drawing therefore relies on a controlled lubricant film rather than on the alloy alone.
| Process parameter | Typical practice for thin foil |
|---|---|
| Lubricant viscosity | 2-10 mm2/s at 40 C, applied as a uniform film |
| Die surface roughness | Ra 0.2-0.4 um, polished in the direction of metal flow |
| Die clearance | 1.1-1.3 times the foil thickness |
| Die entry radius | generous, to spread the bending strain over a longer arc |
| Blank holder force | minimum load that prevents wrinkling of the flange |
For pharmaceutical and food-contact tooling the lubricant must be pigment free and fully removable by solvent washing or thermal evaporation, and the same applies to any residual rolling oil carried over from the mill.
Warm Drawing and Dimensional Stability
Drawing at elevated temperature between roughly 150 C and 200 C lowers the flow stress of aluminium and therefore the punch load, which allows deeper draws in a single pass. Two physical effects must be managed. First, the coefficient of thermal expansion of aluminium is about 23 x 10-6 per K, so tooling, blank and lubricant have to reach thermal equilibrium before the first stroke if gauge accuracy matters. Second, recovery begins to soften heavily cold worked foil above about 150 C; soft O temper material therefore loses strength quickly when warm drawn, and the process is usually reserved for H-temper foil drawn in one or two passes with the temperature kept as low as the press allows.
Defect Control in Multi-Stage Drawing
Most rejections in foil drawing fall into four groups, and each has a distinct countermeasure.
Wall thinning and tearing at the die radius: reduce the per-stage reduction, increase the die radius, improve lubricant distribution.
Earing and uneven rim height: adjust the final rolling texture and, where necessary, rotate the blank between stages.
Orange peel and surface roughening: coarsened grain from an inadequate final reduction or from a held interanneal.
Pinholes and pinhole growth: inclusions and coarse second-phase particles in the cast stock, controlled by melt filtration and by limiting the inclusion content of the input slab.
Incoming inspection of the coil, covering gauge profile, surface condition and mechanical values in the drawing direction, removes most of the variation before the press is set.
Applications and Selection Guidance
The combination of high elongation, low earing and stable gauge makes 8079 a standard choice for drawn aluminium packaging and barrier components, including pharmaceutical blister cavities, smooth-wall and wrinkle-wall foil containers, food tray lids, laminated battery pouches, capacitor cans, cable wrap and heat exchanger fins.
Selection is straightforward: choose O temper for deep smooth-wall containers and for cavities that need maximum formability; choose H22 or H24 for shallow, more rigid lids and trays; choose H18 where stiffness and flatness matter more than formability, for example in laminating and in fins. Where a barrier function is critical, foil cleanliness and pinhole performance should be specified alongside the mechanical values, because both are set by the cast and rolling route rather than by the drawing operation alone.
Frequently Asked Questions
Q: What alloy family does 8079 foil belong to?
It is a non-heat-treatable Al-Fe-Si foil alloy with iron of 0.70-1.30 % and silicon of 0.05-0.30 % as the only deliberate additions, in the same family as 8011 and 1235 foil.
Q: Can 8079 foil be hardened by heat treatment?
No. The alloy contains no magnesium and no copper in useful amounts, so there is no precipitation hardening reaction available. Strength is set by cold reduction and temper only.
Q: What draw depth is realistic in a single pass?
Shallow and medium cups up to roughly half a diameter are normally drawn in one pass in the soft temper. Deeper parts are produced in two or more stages, usually with an interanneal between the heavier reductions.
Q: Which standard covers foil mechanical properties?
Tension testing of thin foil follows ASTM E345, foil specification requirements are given in ASTM B479 and EN 546-2, and GB/T 3198 applies to the domestic market. Composition is quoted to EN 573-3.
Q: Does the drawing lubricant have to be removed?
Yes for pharmaceutical, food-contact and battery applications. Specify a pigment-free lubricant that can be fully removed by solvent washing or thermal evaporation, and confirm removal by a residual-oil measurement on the finished part.
Q: Why does earing matter in foil drawing?
Earing produces an uneven rim and uneven wall height, which forces extra trimming, wastes material and can cause local thinning. A fine, uniform grain structure and a balanced rolling texture are the practical controls.