Casting is a simple and very cheap way of forming aluminum—so it is not surprising that it was also the first method used. Such items as children’s toys like cars, dolls, baby rattle, and the kitchen wares and utensils like pots, boilers, ladles and tea kettle were all produced by aluminum casting. Today, casting is the most widely used method of forming aluminum. There may be few changes in the technical aspects, that have been made, but the principle remains the same: molten aluminum is poured into a mold to duplicate a desired pattern.
One of the metals that can be used in all processes to cast metals is aluminum. The different processes of casting aluminum are die casting, permanent mold casting, sand casting either green sand and dry sand, plaster casting, investment casting, and continuous casting.
However, it should be kept in mind that in die casting, although cooling rates are very high, air is trapped in the casting and increases a significant amount of porosity in the middle. It is difficult, if not impossible to eliminate porosity completely and die castings are usually of less strength than permanent mold castings which are gravity fed or are under lower pressure.
There are many factors to consider in selection of a casting process for producing a specific aluminum alloy part. The most important factors for all processes in casting aluminum are feasibility and cost factors and quality factors. For a large volume of castings, however, the casting method to be used must be determined by the design or dimension of the final output. Since 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 aluminum process. Quality refers to both degree of soundness or freedom from porosity like cracking, and surface imperfections and levels of mechanical properties such as strength and ductility.
Cast aluminum transmission housings and pistons have been commonly used in cars, trucks and other vehicles throughout the world for many years. Still, many other engine parts are also from casting aluminum, and the applications grow as car manufacturers seek new ways to save weight and gain fuel efficiency and performance.