What does the second number in an aluminum alloy designation code signify?

The second number in an aluminum alloy designation code indeed signifies any added element to the main alloy. This code helps identify the specific alloy’s composition, indicating the presence of alloying elements that enhance certain properties of aluminum, such as strength, corrosion resistance, and workability.

In the Aluminum Association designation system, alloys are categorized into different series based on their principal alloying element. The first digit indicates the series or main alloying element, while the second number indicates any significant additional elements that enhance specific characteristics of the alloy. Understanding this designation is crucial for selecting the appropriate alloy for various applications in Navy aviation, focusing on performance, durability, and safety standards.