Bimetals and Clad Alloys

Bimetals and clad alloys consist of two or more different alloy layers that are integrally bonded into a metal plate, strip, sheet, or other stock shape. There are many different types of products. Bimetals consist of two metal layers with different coefficients of thermal expansion (CTE). They bend or deflect due to the CTE differences between the layers. Most bimetals are used in temperature indicating, thermostat, and thermal actuator applications. Many circuit breakers are equipped with bimetal actuators that detect heating from overload conditions and mechanically trip the circuit-protection device. Clad alloys are metals that combine one or more corrosion-resistant or wear-resistant outer layers with a lower-cost inner core (such as stainless steel layers) sandwiching a carbon-steel core. Specialty bimetals and clad alloys are often available.

Selecting bimetals and clad alloys requires an analysis of application requirements and supplier capabilities. Choices may include copper and stainless steel; steel and aluminum; copper and nickel (cupronickel); iron-nickel-chrome; titanium, copper, and nickel; and nickel, stainless steel and copper. Copper and stainless steel bimetals and clad alloys are used when appearance, corrosion resistance, formability, and strength are important considerations. Clad alloys that consist of steel and aluminum or stainless steel are aluminum are used in vehicle bumpers, cookware, transition materials, and catalytic converters. Copper and nickel clad alloys are common in coinage. Iron-nickel-chrome is suitable for thermal controls and protectors. Bimetals and clad alloys that are made of titanium, copper, and nickel are often found in aircraft engine exhaust systems. Button cell batteries contain nickel, stainless steel, and copper.

Bimetals and clad alloys are formed into various shapes and sizes, and according to different standards and specifications. Forms may include semi-finished shapes or mill stock, fabricated parts and shapes, flats and rectangular bars, squares and square bars, hex bar stock, plates, rods and round bar stock, and spheres. Bimetals and clad alloys may also adhere to designations and standards from the American Iron and Steel Institute (AISI), the American Society for Testing and Materials (ASTM), and the Society for Automotive Engineers (SAE). Some products comply with Japanese Industrial Standards (JIS), European Norm or EuroNorm (EN), or the Unified Numbering System (UNS).

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