Description

Metal foils and foil stock are very thin, metal-mill products with a thickness that is usually less than 0.006 in. Copper foil and aluminum foil are the most common types of metal foils and foil stock.

How Metal Foils and Foil Stock are Made

Producing and manipulating metal foils and foil stock involves a number of different processes. They include casting processes, joining and assembly processes, deformation processes, material removal processes, heat treating processes, and finishing processes.

• Casting processes involve pouring molten metal into a mold cavity where, once solid, the metal takes the shape of the cavity. Continuous casting processes allow continuous production of stock shapes. Casting is used to make ingots which are then rolled to make metal foils.
• Joining and assembly processes include welding, soldering, brazing, fastening, and other processes that connect parts permanently or semi-permanently to form a new entity.
• Deformation processes include metal forming, roll forming, extrusion, forging and sheet metalworking processes. They use plastic deformation, where deformation is induced by external compressive forces exceeding the yield stress of the material. Rolling is the standard process used to fabricate metal foils.
• Material removal processes remove extra material from the workpiece in order to achieve the desired shape. They include machining operations, abrasive machining, and nontraditional processes utilizing lasers and electron beams.
• Heat treating processes include annealing, quenching, tempering, aging, homogenizing, solution treating, and precipitation hardening. Heat treating modifies the strength, ductility, hardness, machinability, and formability of the metal stock
• Finishing processes engineer the structure of the surface to produce the desired surface finish, texture, corrosion resistance, and fatigue resistance of metal shapes.  Polishing, burnishing, peening, galvanizing, painting, oiling, waxing, lubricating, plating, and coating are types of finishing processes.

Selection Criteria

Selection of metal foils and foil stock is usually based first on a design’s required size and shape, and then on either material types or grades as certain design specifications or application constraints require. Substitute materials can be selected and qualified based on the required material properties. Laboratory, performance, or field testing is used to verify performance in some cases.

Sizes and Dimensions

The GlobalSpec SpecSearch Database contains the ability to select parts based on shapes and dimensions. Dimensions for metal foils and foil stock include overall thickness, gauge thickness, overall width or outer diameter (OD), secondary width, and overall length.

Types of Metals and Alloys

The GlobalSpec SpecSearch Database contains information and listings for different metals and alloys. Each can be classified as either a ferrous or non-ferrous metal.

Ferrous metals and alloys are metals containing iron as the base metal in the alloy. The most common types of ferrous metals are steels such as stainless steel, carbon steel, tool steel, alloy steel, maraging steel, or specialty steels. They are used in countless applications as construction materials, medical devices, tools, magnetic cores, wires, and in the aerospace, military, and medical fields. However, ferrous metals are not generally used in metal foils and foil stock except as alloying additives in special cases. For more detailed information on the individual types of ferrous metals, please visit GlobalSpec’s “Ferrous Metals and Alloys” Learn More page or search for a specific metal or alloy of interest.

Non-ferrous metals and alloys are metals that do not incorporate iron as the base metal. The most commonly materials used for metal foils are aluminum and copper. Some precious metals (silver and gold) are used to make specialized foils. Common applications of foils are as contact materials, insulation, art, and cooking. For more detailed information on individual types of non-ferrous metals, please visit GlobalSpec’s “Nonferrous Metals and Alloys” Learn More page or search for a specific metal or alloy of interest.

Important Mechanical Properties

When selecting metal parts, there are other specifications that must be met besides size and shape. The GlobalSpec SpecSearch Database allows the user to search for a metal shape based on a number of different mechanical properties. These include tensile strength, yield strength, elongation, and tensile modulus.

• Tensile strength or ultimate tensile strength (UTS) at break is the maximum amount of stress (force per unit area) required from stretching or pulling to fail (necking) or break the material under tension-loading test conditions. It is an intensive property and therefore does not depend on size, but is affected by surface defects and the temperature of the environment. This property is primarily used in the design of brittle members where breakage of a material from stretching is a concern.
• Yield strength (YS) is the maximum amount of stress (force per unit area) required to deform or impart permanent plastic deformation (typically of 0.2%) in the material under tension-loading test conditions. The yield point occurs when elastic (linear) stress-strain behavior changes to plastic (non-linear) behavior. Ductile materials typically deviate from Hooke's law or linear behavior at some higher stress level. Knowledge of the yield point is vital when designing a component since it generally represents an upper limit to the load that can be applied.
• Elongation is the percent amount of deformation that occurs during a tensile test or other mechanical test. Ductile materials will be more inclined to deform than to break. Designs that require metal parts to fit and maintain a fixed shape under stress should consider the part’s elongation properties.
•  Tensile modulus or Young's modulus is a material constant that indicates the variation in strain produced under an applied tensile load. Materials with a higher modulus of elasticity have higher stiffness or rigidity.

It is important to consider the testing conditions under which the properties of a material have been found. Operating conditions that differ from the testing environment may have adverse effects on a material’s properties.