Aluminum is strong, lightweight, corrosion-resistant, and inexpensive, making it a highly versatile and effective material for both 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 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, workability, and other properties. Therefore, it is important 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 alloys with the same first digit have similar properties and can be considered to be in the same family or series.
In this post, we’ll look at the seven series of aluminum alloys, their shared properties and applications, and the difference between wrought and cast aluminum. We’ll also provide some guidance on which aluminum alloy to use for your application.
The 1xxx series alloys, or commercially pure aluminum, are at least 99.0 percent pure aluminum. Commercially pure aluminum is very soft and ductile and has excellent corrosion resistance, workability, and thermal and electrical conductivity. For this reason, the 1xxx series is commonly used for electrical transmission lines.
In general, softer aluminum alloys like the 1xxx 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. The 1xxx series is not heat-treatable, as there are no significant alloying elements to affect its structure.
The 2xxx series contain copper as the main alloying element, which gives them a good combination of strength and toughness. However, they’re not as resistant to atmospheric corrosion as most other aluminum alloys, so they are usually painted or clad with a more corrosion-resistant alloy. 2xxx series alloys, especially 2024, are widely used in aerospace applications for their high strength-to-weight ratios.
2xxx series alloys tend to machine well, are very malleable in the fully annealed temper, and can be heat-treated after forming to significantly increase their strength. However, they are the least weldable group of aluminum alloys and are very susceptible to hot cracking.
Manganese is the primary alloying element in the 3xxx series, a group of medium-strength, corrosion-resistant aluminum alloys. 3003 is a common, versatile alloy often used for general purposes because it has decent strength and good workability. Another 3xxx series 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 have fair machinability, but they are less machinable than other, harder alloy series. They are generally not heat-treatable.
The 4xxx series alloys contain silicon as the main alloying element, which lowers the melting point while maintaining ductility. They are typically used as welding wire or brazing fillers rather than base materials. Alloy 4043 is one of the most common fillers for welding 6xxx series alloys. 4xxx series alloys are not heat-treatable.
The 5xxx series alloys contain magnesium as the primary alloying element. 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, storage tanks, pressure vessels, and marine applications.
5xxx series alloys have excellent formability, weldability, fairly good machinability, and are not heat treatable.
The 6xxx series alloys—the most popular and versatile group of aluminum alloys—contain both magnesium and silicon as alloying elements. They have moderately high strength coupled with excellent corrosion resistance.
6xxx series alloys are heat-treatable, highly formable, and have good weldability and machinability, making them great materials for a wide variety of uses. The most common aluminum alloy, 6061, is used for aircraft, automotive and marine frames, architectural structures, 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.
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 applications in the aircraft, aerospace, and sporting equipment industries.
The 7xxx series alloys have different properties depending on the alloying elements. Their high strength makes them difficult 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 grades, they tend to machine well. The 7xxx series is heat-treatable.
Wrought vs. Cast Aluminum
All the above alloy designations are for wrought aluminum, which is worked in the solid form with techniques like rolling or extrusion. However, there are also designations for cast aluminum alloys. Cast aluminum is melted in a furnace and poured into a mold, which gives it very different properties.
The cast aluminum alloy designation system is based on the format xxx.x. Just 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. They tend to have lower tensile strength than wrought aluminum because of casting defects, so they are not usually used for structural applications. 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.
Aluminum tooling plate is generally cast, as the casting process allows for very precise flatness and thickness tolerances. Mic-6 is an example of a cast aluminum tooling plate made of a 7xx.x alloy. Mic-6 tooling plate is known for its outstanding stability and tightly controlled flatness and thickness resulting from the 7xx.x alloy’s high strength and the carefully controlled process used to cast it.
Which Aluminum Alloy to Use
Industrial Metal Service specializes in supplying aluminum to machine shops, fabricators, and manufacturers in the San Francisco Bay Area and worldwide. We stock an extensive inventory of aluminum alloys, including both new materials sourced from U.S. mills and verified aluminum alloy remnants, which offers considerable savings compared to new material. We can provide aluminum cut to the exact dimensions required for your process with our precision cut-to-size sawing services.