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What Is The Aluminum Numbering System?


Aluminum is one of the most amazing metals on Earth. Since its introduction more than a century ago, it has rapidly transformed nearly every industry thanks to its many beneficial properties, such as a high strength to weight ratio, excellent corrosion resistance, and extreme versatility. Due to this latter characteristic, these days there are so many different aluminum products available on the market, it can be difficult for manufacturers and designers to know which aluminum material is right for which application.

Thankfully, the industry has agreed upon a helpful numbering system that provides a great deal of information to anyone who understands how it works. This system is what scientists and developers use to distinguish the growing quantity of aluminum alloys. It makes it relatively easy to find the material that’s perfect for your job. Today we’re going to discuss this numbering system in the hopes that it will make choosing the right alloy a breeze.

Don’t worry. Even if you still have questions, Clinton Aluminum is here to help. Our friendly and knowledgeable technical professionals are standing ready to assist our customers through every step of the production process, from initial prototyping to after sales service. Contact us today to learn more about how we can help your business succeed.

What do we mean by an aluminum alloy?

An aluminum alloy is distinguished by its chemical composition. As opposed to pure aluminum, an alloy has other elements added to it, creating a new chemistry that enhances the metal’s properties. The elements that might typically be added to aluminum include iron, silicon, copper, magnesium, manganese, molybdenum, and zinc. These added elements may make up as high as fifteen percent of the total weight of the alloy.

The surface of an aluminum alloy develops a protective white layer of aluminum oxide. This surface can be augmented or altered with certain anodizing or painting procedures. In most cases, the added elements augment the metal’s strength, but the tremendous diversity of alloys offer manufacturers all kinds of special properties and attributes that can be adapted to pretty much any application or industry.

How does the aluminum numbering system work?

The numbering system that has been widely adopted to classify the growing number of aluminum alloys is administered by The Aluminum Association, which handles their allocation and registration. As of this writing, there are more than 600 different registered aluminum alloys, which can be broadly divided into two categories. There are 400 types of wrought aluminum alloys and another 200 plus alloys that take the form of castings or ingots.

The agreed upon numbering system divides the alloys into distinct groups based upon the primary alloying agent. Also important is the effect of the agents upon the metal’s unique properties, such as the way the alloy responds to thermal or mechanical treatment. Before anything else, the most important factor is whether the aluminum alloy is wrought or cast.

First off, wrought aluminum alloys follow a four-digit identification system, where the first number indicates what the main alloying element is. We normally refer to these alloys according to which series they belong to, such as the 1000 series or the 5000 series. In total, there are 8 different wrought aluminum series, 1xxx to 8xxx.

The second digit, if it’s not 0, indicates that the alloy has been modified from its base form in some manner, and the third and fourth digits are used to identify individual alloys. So as an example, for aluminum alloy 2124, the 2 indicates it is from the 2000 series, which has copper as the principle alloying agent, and the 1 indicates it is the first recognized modification of the original 2024 alloy.

It should be noted that the lone exception to the above system involves the 1xxx series, which are the pure aluminum alloys made up of at least 99% aluminum. The last two digits in this series indicate the minimum aluminum percentage above 99%. So, for alloy 1050, there is 99.50% minimum aluminum.

Besides the first two series, the others by main alloying agent are 3000 (manganese), 4000 (silicon), 5000 (magnesium), 6000, (magnesium AND silicon), 7000 (zinc), and 8000 (all other agents).

 What is the system for cast aluminum?

In contrast to the wrought aluminum designation system, the one for cast alloys is based on a 3-digit plus decimal designation xxx.x. Again, the first digit refers to what the principal alloying element is. It’s important to note the initial digits might refer to different agents in the two systems, so 1xx.x is still pure aluminum (99 percent or more) and 2xx.x is still copper, but 3xx.x is for silicon plus copper and/or magnesium, 4xx.x is for silicon alone, 5xx.x is magnesium, 7xx.x is zinc, 8xx.x is tin, and 9xx.x is for other alloying agents.

The second and third digits again indicate the specific alloy in the series, while the number that comes after the decimal point refers to either a casting (.0) or an ingot (.1 or .2). Furthermore, if there is a capital letter that comes before the number, this means there has been a modification to the alloy.

How do you know what temper an alloy is?

Not every aluminum alloy series is heat treatable. The 1xxx, 3xxx, and 5xxx series are generally not heat treatable, while the 4xxx series has some alloys that are heat treatable and others that are not.

To indicate what kind of heat treatment has been done to the alloys, letters are appended to the end. F is used to indicate as fabricated, meaning no special heat treatment has been applied. O means the alloy has been annealed, normally to improve ductility and dimensional stability. H is strain hardened, and the H is always followed by two digits that provide more information about the treatment. W means the alloy has been solution heat treated, while T indicates it has been thermally treated. The T is also followed by one or more digits that offer more information.

So those are the basics when it comes to the aluminum numbering system. It may seem complicated, but we’re here to help make sure all of our customers find the best alloy for their particular application. Contact us today for more information.

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