Cast aluminum is used to produce everything from cookware to automotive engine blocks. The light weight and high strength of aluminum alloys provide significant advantages when designing cast aluminum parts.
The automotive industry is the largest market for aluminum casting. Cast products make up more than half of the aluminum used in cars. Cast aluminum transmission housings and pistons have been commonly used in cars and trucks since the early 1900s. Parts of small appliances, hand tools, lawnmowers and other machinery are produced from thousands of different unique aluminum casting shapes.
In addition to its inherent physical properties, aluminum is often used because it is a sustainable metal. Aluminum is 100% recyclable without loss of the metal’s properties. Nearly 40% of the North American aluminum supply is now created through recycling processes.
The three most prevalent methods of aluminum casting are sand casting, permanent mold casting and die casting. Many aluminum alloy castings can be produced by any of the available methods. For a considerable number of castings, however, dimensions or design features automatically determine the best casting method.
For example, because metal molds weigh from 10 to 100 times as much as the castings they are used in producing, most very large cast products are made as sand castings rather than as die or permanent mold castings. Small castings usually are made with metal molds to ensure dimensional accuracy.
Quality factors are also important in the selection of a casting process. When applied to castings, the term quality refers to both degree of soundness (freedom from porosity, cracking, and surface imperfections) and levels of mechanical properties (strength and ductility).
The casting method can have a significant impact on product quality. For instance, the high cooling rates for die cast parts tend to trap air in the casting, which results in appreciable amounts of porosity at the center. Therefore, die castings often are lower in strength than low-pressure or gravity-fed permanent mold castings, which are more sound in spite of slower cooling.