Aluminum Etc.: Explaining series numbers that differentiate aluminum alloys, Part I

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In 1954, 75 chemical compositions were identified as part of the introduction of series numbers to differentiate aluminum and aluminum alloys. More than 600 new chemical compositions have been added since then. Currently, there are 400 wrought aluminum and aluminum alloys and 200 aluminum alloys in the form of ingots and castings, with more added every year. Aluminum is separated into wrought and cast aluminum categories and differentiated using a temper designation system.

A quick overview:

While this system is very helpful to a welding engineer, it can be a bit overwhelming for the typical welder, who is just trying to get their project completed.

So how do you know which aluminum series to use?

First, let's break down the four-digit identification system specific to wrought (cast has a three-digit system and a decimal—more on that later). The first digit (XXXX) is the principal element that was added to the aluminum. The second digit (XXXX) is a modification of the specific alloy, unless it is 0. The third and fourth digits (XXXX) identify a specific alloy and are considered arbitrary numbers.

Using 5356, a commonly used aluminum series, as an example, the 5 indicates that magnesium is the principal element added to the aluminum; the second digit, 3, lets us know that manganese was added to the magnesium; and the last two digits, 5 and 6, identify the 5000 series.

Alloy series 1XXX has 99% aluminum as its principal alloying unit—this is essentially pure aluminum. In 2XXX, the principal alloying unit is copper; in 3XXX, it's manganese; in 4XXX, it's silicon; in 5XXX, it's magnesium; in 6XXX, it's magnesium and silicon; in 7XXX, it's zinc; and in 8XXX, it's "other elements."

In today's welding world, some series are more user friendly than others. Hot cracking and stress corrosion are huge factors as to why we can arc weld some series while others are considered unweldable.

As technology advances and more procedures and processes are discovered and used, understanding aluminum alloys and applications will become more important to the future of manufacturing.

I know from my time in industry that understanding the aluminum identification/designation system eludes the average fabricator and welder. We often rely on what has worked and hope it continues to work!

Breaking down what all of those numbers mean, the alloy temperatures between wrought and cast aluminum, and what makes some aluminum alloys nonheat-treatable will take more than one column. I am ready to deep dive into this subject!

Please feel free to contact me about aluminum-specific information that you have always wondered about or a project you are working on.