Aluminum Alloy: Types, Properties, and Applications
Aluminum alloys are incredibly durable, lightweight, and versatile. For these reasons, they’re widely used in manufacturing all kinds of components in the aircraft, automotive, marine, and railway industries. This guide will walk you through the different properties, features, types, and applications of an aluminum alloy.
The History of Aluminum Alloy
1825 - Hans Christian Oersted
Danish physicist Hans Christian Ørsted was the first to isolate pure aluminum in 1825. He did this by mixing aluminum chloride (AlCl3) with potassium amalgam (KHg2), which is a silver-colored compound with a melting point of approximately 532°F (278°C).
1827 - Friedrich Wöhler
The German chemist Friedrich Wöhler continued the work of Hans Christian Ørsted. But instead of potassium, Woehler used sodium to extract a pure sample of aluminum in 1827.
1856 - Henri Étienne Sainte-Claire Deville
During these times, the cost of aluminum was higher than that of tin and gold. This element is also difficult to work with.
Henri Étienne Sainte-Claire Deville played an important role in decreasing the cost of aluminum. The French chemist developed a cost-effective process for making aluminum on an industrial scale in 1856.
However, the aluminum metal he produced still commanded a steep price of $40 per kilogram. That was in 1859.
1886 - Charles Martin Hall
Charles Martin Hall developed a method that made inexpensive commercial production of aluminum possible. He patented this method on April 2, 1889. Hall’s method uses electric current (electrolysis), which passes through a non-metallic conductor (liquified sodium fluoride), to produce the right conditions to extract pure aluminum from its ores.
With the backing of financier Alfred E. Hunt, Charles Martin Hall established the Aluminum Company of America (then called Pittsburgh Reduction Company). By 1914, Hall successfully brought the price of aluminum down to 18 cents per pound.
1909 - Alfred Wilm
In 1909, German metallurgist engineer Alfred Wilm patented the first strong and lightweight aluminum alloy—the “Duralumin.” (The name is a combination of Dürener and aluminum.) Wilm developed Duralumin for aircraft, military, and industrial applications.
What Is Aluminum Alloy?
Aluminum alloy is a type of metal that commonly contains two or more elements, such as chromium, copper, magnesium, manganese, silicon, zinc, and other elements. Pure aluminum serves as the base metals. These alloying elements can change aluminum’s characteristics and improve its performance based on its intended uses.
The number of elements you add in specific amounts to aluminum will vary. It depends on your desired properties of the alloyed aluminum to suit a particular application.
For instance, you can combine chromium with aluminum to increase corrosion resistance. Or, you can mix it with magnesium to produce an alloy with high tensile strength and a light weight.
Characteristics of Aluminum Alloys
Aluminum alloys are used in various industries because of their desirable properties, including:
Corrosion Resistance
Aluminum and its alloys are naturally resistant to corrosion because they form a thin oxide layer on their surface. This layer helps prevent corrosion and rust.
Lightweight
Aluminum alloys have a low density. That’s why they’re light. The lightest aluminum alloy is called “aluminum lithium alloy,” which is lightweight and strong at the same time. For this reason, they’re widely used in the aerospace industry.
High Ratio of Strength to Weight
Despite being lightweight, aluminum alloys are stronger and more durable than many other materials of comparable density. This is due to the combination of aluminum with other elements, such as copper or zinc.
Malleable
While aluminum alloys are not as soft or flexible as other materials, they’re easily shaped and formed without breaking or cracking. This makes them a valuable option in construction and manufacturing.
Heat Conductivity
This refers to the ability of aluminum alloys to efficiently transfer heat. The high heat conductivity of aluminum alloys makes them a popular choice for applications or products that require efficient heat dissipation, such as in car radiators, cooking utensils, and electronic devices.
What’s the Difference Between Aluminum and Aluminum Alloy?
Some people often confuse aluminum and aluminum alloys because of their similar appearance and applications across different industries. These two metals are different in many ways, including their composition, characteristics, and applications.
Aluminum
Aluminum (Al) is a silvery-white pure metal that has a 99% or higher purity level. It’s lightweight, non-magnetic, and soft. It also has a low melting point, which is why it’s easy to melt and shape without breaking. In its pure form, aluminum is usually used in non-load-bearing applications, such as in the production of cables, cans, electronic components, foils, wires, household items, and packaging materials.
Aluminum Alloy
Alloy steel and aluminum alloys aren’t considered pure metals because they consist of one, two or more metals. Aluminum in its pure form is combined with other metals to create a resulting material with improved properties, such as increased corrosion resistance, hardness, and strength.
The specific amount of aluminum or alloyed components in an aluminum alloy completely varies, depending on the formulation and desired characteristics of constituent materials. In general, pure aluminum makes up most of the mixture, while the rest is composed of other alloying elements.
Which Is Better, Aluminum or Aluminum Alloy?
The answer is, it depends on the intended application.
When it comes to price, raw aluminum is usually more affordable than aluminum alloy, stainless steel, and other common alloys. (Although it’s more expensive than carbon steels.) This is because raw aluminum has a simpler composition, with fewer extra components, so it’s easier and more cost-effective to produce.
Raw aluminum usually has a low melting point, which makes it malleable. But its softness is also one reason why it’s not durable and strong enough for most industrial applications.
An aluminum alloy is thirty times stronger than aluminum and even beats steel in terms of strength-to-weight ratios. But in general, carbon steel (which predominantly consists of pure iron atoms) is still stronger than aluminum alloys when it comes to hardness and tensile strength.
Raw aluminum is more corrosion-resistant than these alloys because it creates an oxide layer that stops further corrosion or oxidation. On the other hand, the additional elements in an aluminum alloy could change the properties of base metal on its surface, preventing it from forming a protective oxide layer.
Overall, raw aluminum is valued for being corrosion-resistant and lightweight. Due to its alloying elements, an aluminum alloy tends to be stronger, more durable, and more versatile. Manufacturers can also customize the composition of aluminum and steel alloys to meet the specific performance requirements of different industries.
Different Types of Aluminum Alloy and Their Properties
There are different ways to classify aluminum alloys. For instance, they can be classified depending on how other metals are mixed in:
Interstitial alloys: An interstitial alloy is created when smaller atoms (or smaller carbon atoms in the case of steel) from one element occupy the gaps in a metal structure.
Substitutional alloys: With this type of aluminum alloy, various atoms take the place of some of the original atoms in a metal.
Table 1: Physical Properties of Aluminum Alloys
The degrees of freedom in the mechanical engineering context for the two fits are different. For press fit, the only degree of freedom available is in the axial direction. With the rotational movement restrained, this fit provides the required resistance and stability.
For the clearance fits, there is more degree of freedom. Because the hole and shaft connect more loosely, there is more movement and flexibility. This can equally be advantageous in some instances.
Another way to categorize an aluminum alloy is based on how it’s processed:
Wrought alloys: These alloys are mostly made of aluminum. Some of them undergo further heat treatment methods in order to become stronger, while others don’t. Manufacturers usually use these for shaping purposes, such as extrusion, rolling, and shaping.
Casting alloys: Compared to wrought alloys, casting alloys contain more alloying elements. Since they’re meant for casting, they need to have low melting points and low expansion rates (how much they increase in size). But one of their disadvantages is that they usually have a lower tensile strength (the ability to withstand being pulled apart without breaking) than wrought alloys.
Table 2: Chemical Properties of Aluminum Alloy
The degrees of freedom in the mechanical engineering context for the two fits are different. For press fit, the only degree of freedom available is in the axial direction. With the rotational movement restrained, this fit provides the required resistance and stability.
For the clearance fits, there is more degree of freedom. Because the hole and shaft connect more loosely, there is more movement and flexibility. This can equally be advantageous in some instances.
An aluminum alloy is also available in various grades. Let’s discuss some of them below:
1000 Series
The 1000 series is a kind of aluminum alloy that consists of 99% or higher pure aluminum, with other elements present in small quantities. Some of the representatives of this series include 1060 and 1070, which are known for their remarkable ability to conduct electricity and heat. The 1100 series, which is also called commercially pure aluminum, is the softest of the common alloys.
2000 Series
The main alloying element of the 2000 series is copper. Alloys from the 2000 series, such as 2011, are widely used for the production of machine components and transportation equipment. Duralumin (2017) and super duralumin (2024) alloys used to be common in the aerospace industry. But since they’re prone to corrosion and cracking under stress, they’re now being replaced with the 7000 series in more recent designs.
3000 Series
The aluminum alloys in this series are primarily alloyed with manganese, which is responsible for their excellent corrosion resistance. These alloys are suitable for applications where they’re going to be exposed to harsh environments.
3003 aluminum alloy is the most common variety in this category. It’s stronger than a 1100 aluminum alloy by 20%, making it a good all-around alloy for applications that require moderate strength levels.
4000 Series
The 4000 series contains high levels of silicon (Si), which is why it’s also called a silicon alloy. These alloys don’t easily crack at high temperatures and have low melting points, making them an excellent choice for welding and brazing applications. They’re also used in marine applications, architectural applications, automotive parts, electrical conductors, and heat exchangers.
5000 Series
The 5000 series, which is also known as marine-grade aluminum, is alloyed with magnesium. Alloys in this series aren’t only resistant to corrosion, but they’re also known for their excellent strength. Thus, they’re commonly used in applications where both strength and corrosion resistance are important, such as in building bridges, tanks, and vessels.
6000 Series
This family of aluminum alloys contains two primary alloying elements: magnesium and silicon. These elements give these alloys their strength and malleability characteristics. The most popular aluminum alloy in this series is 6061, which is commonly used in the aerospace, automotive, and construction industries because it’s easy to weld and work with.
7000 Series
The 7000 series is one of the strongest groups of commercial-grade aluminum alloys on the market. This series has two groups: one alloyed with copper, magnesium, and zinc, while the other group is alloyed with magnesium and zinc. Due to their high strength levels and light weight, these alloys are often used in aircraft structures and high-stressed components.
Applications of Aluminum Alloy
Aluminum alloys are incredibly diverse and versatile metals, with a wide range of applications across many industries. Some of their key applications and users include the following:
Aircraft Applications
Some of the common aluminum alloys used in the aircraft industry are 2024, 7075, 6061, 7050, and aluminum-lithium alloys. These alloys play a crucial role in the construction of aircraft and their components because they’re resistant to corrosion, have a good weight-to-strength-to-cost ratio, and are easy to shape.
Automotive Parts
Aluminum alloys are often used in manufacturing different automotive parts, such as engine blocks, body panels, wheels, and suspension system parts. Thanks to their corrosion resistance, light weight, and strength, these alloys help improve the fuel efficiency, handling, and performance of vehicles.
Bicycle Frames
The material and construction of a bicycle frame greatly affect how well it performs, how comfortable it is to ride, and how safe it is. The lightweight properties of aluminum alloys, such as 6061, 7046, and 7005 alloys, contribute significantly to the maneuverability, speed, and responsiveness of most bicycles. And even though they’re lightweight, aluminum frames are incredibly rust-resistant and strong.
Construction
When it comes to construction, the aluminum alloys most companies use are the 3,000 series or 5,000 series. But between the two alloy grades, the 3,000 series alloys are used more often because they’re easier to assemble, form, or shape during the construction process. You’ll often find these metals in doors, external facades, roofs, shelves, staircase railings, walls, and windows.
There are many types of aluminum alloys available today, each with their own unique properties, strengths, and weaknesses. For that reason, they’re not only used in the aircraft, automotive, bicycle, and construction industries. They also play a crucial role in the production of medical equipment, packaging materials, electrical components, and consumer goods.
Advantages and Disadvantages of Aluminum Alloys
Knowing the advantages and disadvantages of aluminum alloys is important for different reasons. For architects, contractors, engineers, and manufacturers, it can help them choose the right types for specific applications and ensure the safety and reliability of components or parts.
Advantages of Aluminum Alloys
1. Good Corrosion Resistance: It’s important to take note that each aluminum alloy grade provides varying levels of protection from corrosion. Alloy 5052, for instance, is known for its excellent corrosion resistance. This makes it a suitable option for applications where exposure to saltwater or extreme weather conditions is a significant consideration.
2. Lightweight: Compared to carbon steel or stainless steel, aluminum alloy is significantly lighter due to its lower density. This exceptional characteristic of aluminum alloys makes them ideal for applications where weight reduction is crucial for performance and fuel efficiency.
3. High Specific Strength: Despite being lightweight, most aluminum alloys don’t break or crack easily under stress. They can be stronger than pure aluminum by up to thirty times. They can even surpass steel when it comes to strength-to-weight ratios.
Disadvantages of Aluminum Alloys
1. More Expensive: The price of aluminum and its alloys varies with market conditions. Factors that affect their price tag include material costs and the production process. In general, they’re more expensive than carbon steel and cheaper than stainless steel.
2. Difficult to Weld: Among the various alloys, the 2000 series alloys are the least weldable. To be more specific, the 2024 alloys are the most susceptible to cracking when they’re still hot and in a semi-solid state. Some of the aluminum alloys that don’t have the same issue are 2219 alloys and 2519 alloys.
Conclusion
Aluminum alloys, with their long list of distinct characteristics and beneficial properties, are one of the most widely used metals in the world. With the help of ongoing studies, we can expect newer aluminum alloys that have better and more advanced features to meet specific project needs in many industries.
Author
Gavin Leo is a technical writer at Aria with 8 years of experience in Engineering, He proficient in machining characteristics and surface finish process of various materials. and participated in the development of more than 100complex injection molding and CNC machining projects. He is passionate about sharing his knowledge and experience.