Aluminum Alloys The American Foundry Society Technical Dept., Schaumburg, Illinois C
ast aluminum components are used for a wide range of functions, from decorative components, such as lighting fi xtures, to highly engineered,
safety-critical components for aerospace and automotive applications. Many dif- ferent methods and alloys can be used to produce cast aluminum components. The choice of alloy and casting process plays a major role in the procurement process, affecting both component prop- erties and cost. Design engineers should begin the
procurement process for cast aluminum parts by defi ning the three major factors that drive quality and cost—functional- ity (service requirements), design (shape and size) and production quantity. Each of these factors will have a bearing on the choice of casting method, alloy selection and cost, as well as fi nal component quality.
Functionality & Service Requirements
When determining how a component will function, the fi rst question to ask is, what purpose will the component serve? Choosing the alloy, casting process and thermal treatment requires knowl- edge of the service conditions of the proposed part, so defi ning the end-use functions and
requirements is always the starting place in the procurement of an aluminum casting. If high-strength, safety-critical components are required, the number of potential casting processes is narrowed, and a high-integrity casting process, such as permanent molding, premium sand casting or a semi-solid casting process, must be chosen. The alloy selection also cannot be
determined until the component’s ap- plication and end-use requirements are defi ned. The range of possible mechanical properties varies widely because there are many alloy and thermal treatment combinations. For example, many com- mercial castings do not have critical service requirements; therefore, a more economical alloy and production method can be utilized.
Design Once the function of the desired com-
ponent is determined, engineers and purchasers must
ask questions relating to design issues, such as size, weight and part complex- ity. The size and design features of the casting and available alloys can drive the choice of casting process and cost of the component. Sand casting often is used to produce parts with hollow cavities and a complex arrangement of ribs and pockets that make them less suitable for casting in permanent molds, although there are always exceptions to the rule. Design complexities can have vari-
ous effects on component cost. In some cases, the fi nished component cost can be reduced by including features in the design that will produce a near-net-shape cast part and eliminate or minimize ad- ditional costs from post-casting processes, such as machining. However, features like complexity and surface fi nish or special properties can increase the cost of the casting. It also might be advantageous to redesign a casting for a lower cost process,
This motorcycle frame com- ponent was produced via the nobake sand casting process in 356 aluminum with T6 heat treatment temper.
2010 Casting sourCe DireCtory Metal Casting Design & PurChasing 27
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