Bimetallic alloy is a kind of precision alloy, and it is formed by two layers (or several layers) of metals or alloys with different thermal expansion coefficients combined as component layers.

One component layer of the thermal bimetal has low thermal expansion coefficient, called passive layer. The other component layer with high thermal expansion coefficient is called active layer.

The expansion coefficient of each component in this bimetal alloy varies. When temperature changes, the expansion amount or shrinkage amount of each component is different. So the bimetallic element, as a whole, will bend. This thermosensitive property is widely used in temperature measuring, temperature control, temperature compensating, program control, etc. And this bimetallic alloy is widely adopted in thermal relay and circuit breaker of electrical industry, weather instrument and galvanometer of instrument industry, and electric iron,electric cooker, refrigerator and air conditioner of home appliance, etc.