Knowing Which Aluminum Alloy to Use

Aluminum is strong, lightweight, corrosion-resistant, and inexpensive, making it a highly versatile and effective material for prototype and production runs. Its ductility makes it easily formable, and because aluminum alloys chip easily, they are much more machinable than other metals like steel and titanium, prolonging tool life.

However, not all aluminum is created equal. Like most metals, aluminum is usually alloyed with other elements to improve its mechanical properties, and knowing which aluminum alloy to use depends on the specific properties needed. The different types of aluminum alloys vary in strength, corrosion resistance, wear resistance, workability, and other properties. Therefore, it is essential to know the difference between them when deciding which aluminum alloy to use for a particular application.

Wrought aluminum alloys are identified by a four-digit number. The first digit identifies the main alloying element or elements, so aluminum alloys with the same first digit have similar properties and can be considered in the same family or series.

In this post, we’ll look at the seven types of aluminum series, their shared properties and applications, and the difference between wrought and cast aluminum. We’ll also provide guidance on which aluminum alloy to use for your application. Understanding the various types of aluminum available helps make informed decisions about the best material for specific needs. Each of the seven types of aluminum offers unique benefits, making it crucial to select the appropriate one for your project.

1xxx Series

The 1xxx series alloys, or commercially pure aluminum, consist of at least 99.0% pure aluminum. This aluminum purity is very soft and ductile, with excellent corrosion resistance, workability, thermal conductivity, and electrical conductivity. Due to these mechanical properties, the 1xxx series is commonly used for power transmission lines.

In general, softer aluminum alloys like the 1xxx series can be difficult to machine because they tend to form a buildup of melted aluminum on the cutting tool. However, the same properties give the 1xxx series excellent weldability. These aluminum alloys are non-heat-treatable, as there are no significant alloying elements to affect their structure.

The 1xxx series’ high aluminum purity ensures its reliability in various applications, especially where thermal conductivity, electrical conductivity, and excellent corrosion resistance are required. Using a pure metallic element in these alloys highlights their suitability for specific uses, making the 1xxx series a vital choice for applications demanding pure aluminum.

2xxx Series

The 2xxx series contains copper as the alloying element, which gives it a good combination of strength and toughness. However, it does not have superb corrosion resistance as most other aluminum alloys, so it is usually painted or clad with a more corrosion-resistant alloy. 2xxx series alloys, especially 2024, are widely used in aerospace applications in the aerospace industries for their high strength-to-weight ratios.

2xxx series aluminum alloys tend to machine well, are very malleable in the fully annealed temper, and can be heat-treated after forming to increase their strength significantly. However, they are the least weldable group of aluminum alloys and are susceptible to stress corrosion cracking.

3xxx Series

Manganese is the primary alloying element in the 3xxx series, a group of moderate-strength aluminum alloys with good corrosion resistance. 3003 is a common, versatile aluminum alloy often used for general purposes because it has decent strength and good workability. Another 3xxx series aluminum alloy, 3004, is well-known as the material of aluminum beverage cans.

When deciding which aluminum alloy to use, 3xxx series alloys are a good choice for many applications. They are easily formable, weldable, and fairly machinable, but they are less machinable than other, harder aluminum alloy series. They are non-heat-treatable alloys.

4xxx Series

The 4xxx series aluminum alloys contain silicon alloys as the principal alloying element, which results in a low melting point while maintaining ductility. They are typically used as welding wire or brazing fillers rather than base materials. Aluminum alloy 4043 is one of the most common fillers for welding 6xxx series alloys.

The 4xxx series are non-heat-treatable aluminum alloys, meaning they do not undergo heat treatment to enhance their properties. Despite the absence of heat treatment, these aluminum alloys are valued for their specific applications where their unique characteristics are advantageous.

5xxx Series

The 5xxx series alloys contain magnesium as the primary alloying element. Aluminum alloys in this series usually come in sheet or plate and have moderate to high strength and excellent corrosion resistance in marine environments. Because of this, the 5xxx series is widely used in construction materials, storage tanks, pressure vessels, and marine applications.

5xxx series have excellent formability, weldability, and relatively good machinability but are non-heat-treatable aluminum alloys.

6xxx Series

The 6xxx series alloys—the most popular and versatile group of aluminum alloys—contain magnesium and silicon as main alloying elements. They have moderately high strength coupled with excellent corrosion resistance.

6xxx series aluminum alloys are heat-treatable, highly formable, and have good weldability and machinability, making them excellent materials for various uses. The most common aluminum alloy, 6061, is used for aircraft, automotive frames, marine applications, architectural and structural components, industrial machinery, medical and semiconductor assemblies, and countless other uses.

For many customers deciding which aluminum alloy to use in a general application, 6061 is a reliable, readily available choice due to its magnesium and silicon content. This composition makes the 6xxx series aluminum alloys particularly advantageous in applications requiring these properties, as the combination of magnesium and silicon in the alloy helps to form magnesium silicide, enhancing its overall strength and durability.

7xxx Series

The 7xxx series contains zinc as the primary alloying element, and most alloys also contain smaller amounts of magnesium, copper, or chromium. This is the strongest group of aluminum alloys, with some comparable to steel in strength. Their high strength makes them ideal for high-performance aircraft, aerospace, and sporting equipment applications.

The 7xxx series aluminum alloys have different properties depending on the alloying elements. Their high strength makes them challenging to form compared to other aluminum alloys, and most alloys in this group are not weldable. Machinability depends on the alloy, but like most harder aluminum grades, they tend to machine well.

The 7xxx series is a heat-treatable alloy.

Wrought vs. Cast Aluminum

All the above alloy designations are for wrought aluminum alloys, which work in solid form with techniques like rolling or extrusion. However, there are also designations for cast aluminum alloys. Cast aluminum, known for its distinct thermal expansion properties, is melted in a furnace and poured into a mold, which gives it very different characteristics.

The cast aluminum alloy designation system is based on the format xxx.x. Like the wrought alloy series, the first digit represents the main alloying element, and the other digits correspond to the same elements as the wrought alloy series. For example, the 1xx.x series is commercially pure cast aluminum, 2xx.x is cast aluminum alloyed with copper, and so on.

Cast alloys contain larger percentages of alloying elements than wrought alloys, which can significantly affect their thermal expansion. They tend to have lower tensile strength than wrought aluminum because of casting defects, so they are not usually used for structural applications. Despite this, their thermal expansion characteristics make them suitable for specific uses. Cast alloys are cheaper than wrought alloys, and the casting process allows much more flexibility in producible shapes. Cast aluminum parts that require little or no post-casting machining can be produced, taking advantage of their thermal expansion properties.

An aluminum tooling plate is generally cast, as the casting process allows for exact flatness and thickness tolerances. Mic-6 is an example of a cast aluminum tooling plate made of a 7xx.x aluminum alloy. Mic-6 tooling plate is known for its outstanding stability and tightly controlled flatness and thickness resulting from the 7xx.x aluminum alloy’s high strength and the carefully controlled process used to cast it.

Which Aluminum Alloy to Use

Industrial Metal Service supplies aluminum to machine shops, fabricators, and manufacturers in the San Francisco Bay Area and worldwide. We stock an extensive inventory of aluminum alloys, including new materials sourced from U.S. mills and verified aluminum alloy remnants, which offer considerable savings compared to new materials. With our precision cut-to-size sawing services, we can provide aluminum cuts to the exact dimensions required for your fabrication process or manufacturing process.

Whether you need a regular aluminum supply for long-term production, a custom order for a special project, or advice on which aluminum alloy to use, call us, and we’ll help you find the best solution for your needs—fast.