Manufacturers around the globe rely on quality materials to create a range of parts, equipment and products for businesses and consumers. During the assembly process, different materials may need to be joined together for a tight seal, cast in a mold to a designed form, or bent into a new direction without collapsing. Low melting alloys, also called fusible alloys, have a composition that allows the metal to form into a liquid or semi-liquid state at low temperatures and then re-solidify. These low melting alloys are ideal as they allow for parts to be joined or cast at temperatures lower than 300 degrees.
Selecting the right low-melting alloy is essential to ensure that the part which is joined, cast, or bent still maintains its strength and durability for the application. With manufactured equipment and parts going through extreme pressures, stresses and temperatures, you need to have a better understanding about the low melting alloys you select and their characteristics during solidification.
Common Low Melting Alloys and Their Characteristics
There are a wide range of low melting alloys available. Yet some are restricted in their use based on their brittleness, toxicity, and reactive qualities. Some of these elements are bismuth, gallium, tin, indium, zinc, cadmium, tellurium, antimony, thallium, mercury and lead. Many of these minerals may also be additives placed in during the formation of the low melting alloys. Four common base alloys we will discuss today are bismuth, gallium, tin and indium.
Tin-Based: Pewter is one common tin-based low melting alloy that is used. There will normally be a composition base where there will be about 50% tin element in the alloy. Manufacturers select tin due to its malleability when they require a metal that has a ductile characteristic, as it can be molded and shaped without becoming brittle.
Bismuth-based: Bismuth alloys will have a composition that is less of a ductile characteristic than tin, as it can become brittle. Manufacturers use bismuth due to its expansion qualities when it melts and then solidifies as it can expand to up to 3.3%. The more bismuth is in an alloy, the more it expands. It is less expensive than other alloys that are featured and the least toxic as it can be used in applications where there is drinking water present.
Indium-based: Indium alloys can be used when bonding onto gold, glass and ceramic surfaces as well as other materials. It can also weld onto itself and has the ability to wet surfaces that are non-metallic as well as metallic. When looking for a ductile element that offers fantastic fatigue resistance and a variety of low melting points, manufacturers may select indium alloys for their applications.
Gallium-based: Due to its extremely low melting point, gallium-based alloys have the ability to melt when held in a person’s hand. It changes into a liquid at room temperature, as manufacturers will often use it for thermal management applications. It can also be used to wet on nonmetallic and metallic surfaces including glass and porcelain. Like bismuth, gallium can become dense and brittle when solidifying.
One of the main reasons for using low melting alloys is due to how it changes when it melts and then solidifies. Some alloys are eutectic and will become pure liquid instantly, while others are Non-Eutectic and will transition through a semi-liquid state that has a type of slushy texture before becoming liquidous. Low melting alloys will also change in density when solidifying. Alloys such as bismuth and gallium will expand greatly when in their liquid state and then become dense when changing back into a solid.
Knowing the density of the alloy is important as the manufacturer needs to know how much it will shrink or expand. If the metal shrinks too much, it may not create the proper bond with other materials, or have the required strength it needs to withstand stresses. If it expands too much, it can become brittle when changing back into a solid as the alloy might fail during the operation of the product or equipment.
The varying densities of the alloys can also be important to manufacturers based on how they plan to use the alloy. For delicate jewelry, you may not want a material to expand too much as it could end up damaging the surrounding metal that needs to remain intact. You also need to pay attention to the elongation, strength, tensile modulus and yield strength of the alloy during the manufacturing process.
Here at Belmont Metals, we provide a variety of low melting alloys and metals for various applications in the manufacturing process. We have been in business for 121 years as our state-of-the-art facility can provide you with the right low melting alloys for your needs.