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Mar 17, 2023

Aluminum Etc.: Explaining aluminum series numbers for cast alloy designation, Part II

Aleksandr Kondratov / iStock / Getty Images Plus Last time, we broke down the

Aleksandr Kondratov / iStock / Getty Images Plus

Last time, we broke down the alloy temper and designation system of wrought aluminum. In this issue, we dive into cast aluminum.

The cast alloy designation system is based on three digits plus a decimal designation. Much like with wrought aluminum, the first digit in cast indicates the principal alloying agent. The second and third digits represent arbitrary numbers that identify a specific alloy in the series. In both designation systems, the 1, 2, 4, 5, and 7 series used as that first digit are identical primary alloy elements.

In the cast designation system, the remaining four numbers (3, 6, 8, and 9) mean something else:

Where this designation system gets interesting is the number following the decimal point. A 0 after the decimal indicates the aluminum was cast into a working mold. A 1 or a 2 indicates an ingot (pure aluminum mold) and will be reworked into its final product.

Understanding the identification system for wrought and cast aluminum and what each series number says about the different characteristics will help you make good choices for your application. From here you can find the letter specifying temper designations, which are especially helpful when welding on heat-treatable and nonheat-treatable aluminum alloys.

Parts makers use cast aluminum because it produces complex parts with high accuracy, enabling manufacturers to replicate the exact design and reduce the need for machining. Materials made from this metal are lightweight and offer outstanding strength. If we consider its weight-to-strength ratio, cast aluminum parts fare better against any other casting process, including the stronger cast iron. As a result of this, the automobile and aerospace industries use cast aluminum extensively. Many industries prefer parts made from this metal because it is very affordable.

So much of our daily lives revolve around cast aluminum. From pots and pans to engine pistons, there isn't an industry I can think of that doesn't use it in some way.