Alloy Castings

Alloy Castings

Alloy castings may be solid, hollow, flat, spherical, have holes, threading or projections. One of the first and most important steps in die casting is choosing the appropriate alloy. Zinc, aluminum, magnesium, copper, tin and lead alloys are all used to make die castings with many different physical and mechanical properties, including strength, melting point, resistance to corrosion and extreme temperatures, fluidity, ductility, life span, weight, hardness and density. Harder metals like steel and stainless steel are difficult to form via die casting and are rarely used in die casting for that reason. Zinc, lead and tin all have a melting point of less than 723º F and are therefore used in hot chamber die casters, while aluminum, magnesium and copper have melting points ranging anywhere from 800º F to 1,650º F and up. Because they require such high temperatures to be die cast, they are ladled into the mold from a holding pot separate from the furnace in order to prevent cylinder, plunger and pot interior damage.

The most popular die casting alloys are aluminum and zinc followed by magnesium, copper, and then lead and tin. Zinc alloys are simple to die cast, and because they have lower tensile strength, they are not used in large load applications. Pure zinc is alloyed with copper for rigidity, aluminum for strength and tin for added flexibility if needed. The finished zinc alloy product has a smooth surface, consistently thin and uniform walls, and high ductility. Pure aluminum is almost never used for die casting because of its tendency to shrink and crack when solidifying in the mold. It is alloyed with silicone to increase liquid fluidity and copper to increase hardness, reduce ductility and improve corrosion resistance. Aluminum alloy die castings are lightweight, resistant to chemicals, exhibit dimensional stability and are also easy to cast. Copper alloy castings are used in plumbing, electrical, marine and in many other applications because of their high resistance to corrosion, chemicals and moisture. They have the highest strength of any alloy cast, and are able to alloy with iron. Magnesium alloy casts are the lightest, have an excellent strength to weight ratio, and are considered the easiest alloy to die cast. Tin and lead are among the least frequently cast materials and are used in high strength applications. They are high in density and are able to produce parts with complex dimensions.