Why 8079 Foil Is Used for Deep Drawing
Deep drawing is a sheet-forming process in which a flat blank is pushed into a die cavity to form a cup or shell, and the material must stretch, flow and compress without tearing or wrinkling. 8079 is an aluminum-iron-silicon foil alloy with a carefully balanced composition that gives it the formability needed for this demanding process. It is widely used for drawn food containers, closures, blister-pack lids and other components where thin gauge, barrier performance and reliable forming are all required.
Microstructure and Formability
The forming behavior of 8079 foil is controlled largely by its grain structure and texture, which are developed through cold rolling and annealing. A fine, recrystallized grain structure in the range of about 5-15 microns promotes homogeneous deformation during drawing: more grains take part in the flow, strain is distributed evenly, and localized thinning is reduced. The rolling texture of the foil also matters, because it controls how easily the material flows into the die and how it behaves in different directions. Balanced grain size and texture give the foil the right combination of strength for the cup wall and ductility for the flange area, which is the key to defect-free deep drawing.
Mechanical Properties That Matter
In typical soft or lightly work-hardened conditions, 8079 foil shows yield strength in the range of roughly 90-120 MPa and tensile strength of 140-180 MPa, with uniform elongation above 20% in the fully annealed state. Two formability parameters are particularly important for deep drawing. The r-value, or Lankford coefficient, describes the resistance to thinning in the thickness direction; 8079 foil develops high r-values, which means the material prefers to flow in-plane rather than thin, exactly what a cup wall needs. The n-value, or strain-hardening exponent, controls how the material strengthens as it deforms, which delays strain localization and helps distribute the drawing load. Together, a high r-value, adequate n-value and clean, low-roughness surface allow 8079 foil to be drawn to substantial cup depths without failure.
Surface Quality and Its Role
Surface condition is decisive in deep drawing because the foil slides against the punch and die under high pressure. A clean surface with low roughness, typically below Ra 0.2 microns, keeps friction low and prevents galling and local tearing. Surface contamination such as rolling oil residues, dust or oxide debris disrupts the lubricant film and can nucleate cracks, so foil for deep drawing must be handled and stored with care. The thin natural oxide layer on the aluminum surface is usually an advantage: it accepts forming lubricants well and, with the right chemistry, provides effective boundary lubrication without interfering with subsequent bonding or printing.
Lubrication and Process Control
Lubrication is the practical key to consistent deep drawing. A forming lubricant with suitable viscosity and pressure resistance is applied evenly to the blank, often by roller or spray. The lubricant must reduce friction at the blank-holder and die radii while allowing controlled material flow, and it must be compatible with the foil surface and with downstream cleaning or finishing steps. Temperature control is equally important: drawing at or near room temperature keeps the material in its intended strength and ductility window, while excessive heating from high-speed deformation can soften the material and cause dimensional instability. Consistent process parameters, including blank-holder force, punch speed and lubrication quantity, are what turn an inherently formable foil into a reliable production material.
Applications and Selection Notes
8079 deep-drawing foil is used for round and rectangular drawn containers, tray lids, closures and pharmaceutical or food packaging components where the drawn shape must hold a barrier seal. When selecting foil for a drawing application, specify gauge, temper, surface finish and lubrication requirements, and validate the material with tool trials before production because small differences in tooling, press speed and lubricant change the optimum foil condition. Working with the mill to match foil characteristics to the actual tool is the most reliable route to defect-free parts.
FAQ
What makes 8079 different from pure aluminum foil?
8079 contains controlled iron and silicon additions that refine the grain structure and improve drawability, giving it better deep-drawing performance than soft pure aluminum foil of the same gauge.
Can 8079 foil be deep drawn in the fully soft state?
Yes, the soft annealed condition offers the highest ductility and is commonly used for deep drawn cups; harder tempers are used where the part must resist handling loads after forming.
Why does my drawn foil show wrinkles at the flange?
Wrinkling is usually a process issue: excessive blank-holder force is needed, or the blank-holder pressure is too low, the lubricant is wrong, or the tool radii are too small for the material flow.
How is the r-value of 8079 foil determined?
The r-value is measured in a tensile test by comparing width strain to thickness strain in the plastic region; higher values indicate better resistance to thinning and superior drawability.
Does 8079 foil need special handling before drawing?
The surface should be kept clean and dry, free of oil contamination and scratches, and rolls should be stored in their protective wrapping until use to preserve surface quality.
Can drawn 8079 parts be printed or coated?
Yes, drawn parts can be printed, lacquered or laminated after forming, provided the surface is clean and the finishing process is compatible with the foil and lubricant residues.