Have you ever stopped for a moment to wonder about the differences between the various metals we encounter every day?
Take aluminum, for example. Did you know that aluminum is not just one alloy? There are so many different aluminum alloys, each with its own characteristics and capabilities.
You can think of them as different tools in a toolbox. You would not want to use a sledgehammer to hammer in a small finishing nail, right? It is similar to the alloys. There are probably there are two most popular aluminum alloys known to you, the 6061 and 7075 aluminum.
And 7075 aluminum may look and feel similar, but they are in fact quite different in terms of how they behave and their usages. Choosing one is very important.
In this article, we are going to compare these two heavyweights in aluminum alloy and settle the ultimate 6061 Vs. 7075 Aluminum faceoff. We will look at their chemical properties, advantages and disadvantages, and their real-world applications.
By the end of this article, you should be able to identify the properties of each alloy and be able to clearly decide which is best for your next project.
What is 6061 Aluminium Alloy?
First off, let’s talk about our favorite: 6061 Aluminum Alloy. If aluminum alloys were superheroes, 6061 aluminum would be the dependable, all-around hero. It is one of the most versatile and most commonly used heat-treatable aluminum alloys. It can be found in everything from bicycle frames to the framework of buildings.
So, why is it so popular? Well, 6061 is a solid all-around performer. The primary alloying elements of 6061 aluminum, and its properties, are magnesium and silicon. This specific combination means this material has a fantastic set of properties.
It has fair strength, but more importantly, it has excellent corrosion resistance. Aluminum naturally forms a thin, tough oxide layer on its metal surface when exposed to air. This layer is self-forming and can stop further corrosion from occurring.
In addition, this material has excellent workability. It can easily be formed into custom shapes, and it is great for welded assemblies. It has good machinability, which means it is a dream to machine shop. The most common temper you can find is 6061 T6, which is solution heat-treated and artificially aged to achieve the best strength.
What is 7075 Aluminium Alloy?
Next, we meet the 7075 Aluminium alloy. If 6061 is the friendly neighbourhood superhero, then 7075 is the super-strong, heavy ankled superhero called in to do the tough jobs. This material is known for one thing above all else, and that is its strength. In fact, its strength-to-weight ratio can be compared to many categories of steel.
The incredible strength it boasts; the secret to its strength is its chemical composition. The main alloying elements that can be found in 7075 are zinc, magnesium, and copper.
Of those elements, the primary element in 7075 is zinc, and the elevated zinc content provides an enormous increase in strength. Because of these strength characteristics, it is an aircraft-grade alloy and occurs in aerospace & military applications that require high stress and performance characteristics.
That being said, the strength does have some trade-offs. 7075 Aluminium Alloy is harder, making it more difficult to machine and to form into complicated shapes when compared with 6061. It is also not as corrosion-resistant as 6061. The copper in 7075.
The Difference Between 6061 and 7075 Aluminum Alloy
The 6061 is the flexible all-arounder, and the 7075 is the high-strength specialist, but to understand the 6061 Vs 7075 discussion, we need to understand the differences between the two on a point-by-point basis, from where they get their materials to how they are utilized.
Chemical Composition
The biggest difference is really at the molecular level. The Aluminum Association follows a systematic system in assigning alloys to a particular cause based on alloying principles. In the Aluminum Alloy 6061, the major alloying additions are magnesium (approx. 1.0%) and silicon (approx. 0.6%). These alloying elements provide excellent formability and corrosion resistance.
The Aluminium Alloy 7075 has a very different recipe. The prime ingredient in 7075 is called zinc. Zinc is a critical element in the composition of 7075 and comprises a whopping 5.1% to 6.1% of the build of the alloy.
7075 has some magnesium (approx. 2.1% to 2.9%) and some copper (approx. 1.2% to 2.0%) in its composition of alloying elements. It is the combination of these alloying elements and the high zinc levels that help it achieve ultra-high strength levels.
Strength
In an outright battle of strength, 7075 wins by a margin that is not even close. The tensile strength (the maximum stress a material can handle before breaking) and yield strength (the stress it starts to deform permanently) are much higher for 7075.
In the most popular 7075 T6 temper, the yield strength can be over 500 MPa. For reference, in the 6061 T6 temper, the yield strength is usually in the 276 MPa range. In other words, 7075 is almost twice as strong. The high strength of 7075 means that for high-stress applications where failure is unacceptable, 7075 is the only choice. The drawback of the high strength is that in some cases, it has a low fatigue limit and can be more brittle.
Machinability
Machinability is how easy it is to cut, drill or mold the metal to shape when using machine tools. Here is where the tables turn a bit. 6061 is known to have good machinability. It produces nice, manageable chips, and it doesn’t wear out tooling too quickly.
Aluminium Alloy, being a much harder material, is a lot more difficult to machine. It requires more power, slower cutting speeds, and there can be more wear on tooling. Although it can be machined to a high standard, it is just not as forgiving as 6061.
Formability and welding
Formability is the ability of a metal to be bent or formed into difficult shapes without cracking. Once again, 6061 is your champion here. It has good formability, especially in its annealed condition (softer before heat treatment). It can be bent and shaped into any custom shape with relative ease. It is also thought to be weldable, so it is ideal for fabricating welded assemblies like boat hulls or bus bodies.
7075, however, is not your friend when it comes to forming and welding. Without describing it too bluntly, the high strength means it is much less ductile. If you try to bend it sharp, it will crack. It is generally thought not to be weldable as the high heat can compromise its mechanical properties and make it susceptible to cracking.
Corrosion resistance
Here we see another clear win for 6061. Due to its magnesium and silicon content and lack of copper, 6061 aluminum yields exceptional corrosion resistance. The oxide layer that forms on its surface is stable and does a great job of protecting 6061 from the elements. That’s why 6061 is ideal for outdoor applications and marine environments.
Due to the higher zinc content, and more importantly, the copper in 7075, its corrosion resistance is much less, so much so that I think it is very susceptible to stress corrosion cracking. 7075 needs a protective layer, like paint or anodizing, to prevent it from degrading, especially in corrosive environments. You definitely wouldn’t want to use bare 7075 for marine fittings.
Anodising
Anodising is an electrochemical process that builds up the natural oxide layer on the surface of aluminum. This results in a very hard, long-lasting, and corrosion-resistant surface finish. And the anodised layer can be dyed to give a range of colours.
Both 6061 and 7075 can be anodised to a high standard. For 6061, anodising improves its already excellent corrosion resistance. In terms of 7075, anodising is usually critical. An anodised finish provides the required protection layer that is required to protect the metal surface from the surrounding atmospheric conditions. The anodised oxide layer is very hard and assists with wear resistance.
Thermal Conductivity
Thermal conductivity is an indicator of how well a material will conduct heat. Thermal conductivity is an important property for heat sinks or engine parts, etc. The thermal conductivity for 6061 aluminum alloy is significantly higher than 7075. The thermal conductivity for 6061 is generally around 167 W/m K.
Alloy aluminum has a slightly lower conductivity with typical values around 130 W/mK. This is because the additional alloying elements, especially zinc, introduce barriers to heat movement. Therefore, if your application is to impart heat or “get rid of it very quickly,” then 6061 is the better option to use.
Mechanical Properties
To summarise a few, finally, with the most important aspects, both alloys’ densities are very similar; therefore, there is no efficiency gain to be had by choosing one over the other. The key properties we pointed out earlier were strength, hardness, and ductility.
7075 alloy has superior yield strength and tensile strength; therefore, 7075 is a harder material. 6061 alloy has better elongation ( a measure of ductility) and high toughness. The 7075 has slightly greater electrical resistivity when compared to 6061.
Applications of 6061 Aluminium Alloy
Because of its versatile nature, the 6061 Aluminium Alloy finds applications in a tremendous number of products. Here are some of the most common:
Structural Materials: 6061 is widely used for windows and doors in architecture and construction, and for curtain walls.
Transportation: 6061 is found in bicycle frames, scuba tanks, beverage cans, fishing reels, parts for boats and marine rigging, some automotive parts, and bus body frames.
Welded Assemblies: 6061 is preferred for any application that requires welded materials and is strong when welded.
Electronics: 6061 is usually used rather than 6063 because of its increased thermal conductivity, making it more appropriate for heat sinks and electronics chassis.
Consumer Goods: 6061 is used in many consumer goods and commercial products; in every application, it has a distinctive combination of strength, low weight, and ease of workability.
Applications of 7075 Aluminium Alloy
Due to its unique properties, there are fewer applications for the very high-strength 7075 Aluminium alloys than for 6061, but these applications are typically highly specialized, and focus more on performance.
Aerospace applications: 7075 is typically found here, as this is the traditional application for aircraft. It is specified for airplane structures, aircraft wings, and aircraft fuselages, where a high strength-to-weight ratio is of utmost importance. It is a true aircraft-grade material.
Military applications: 7075 has applications in everything from rifles, missile components, and other high-stress military equipment.
High-performance sports equipment: High-performance bicycle components, rock climbing gear, and lacrosse sticks utilize 7075 to take advantage of its strength and low weight. Tooling and Molds: 7075’s strength and hardness make it valuable in tooling applications that involve die casting and injection molding.
High Wear Components: In a few applications, 7075 is also found in other components that are subjected to extreme wear, such as gears or other high-stress components.
6061 vs. 7075 Aluminium: Which Material Should I Choose?
We have finally arrived at the final battle: 6061 vs 7075 Aluminium. The two materials have different attributes; Ultimately, it is about three factors: performance, workability and price.
Here’s a simple breakdown to help you decide.
Use 6061 Aluminium Alloy if:
You want fair, all-around strength, but you don’t need ultimate strength.
Your project involves bending, forming or welding.
The part you’re making will be exposed to the elements outdoors, and you need reasonable corrosion resistance, but don’t want to add a coating.
Price is a significant consideration (6061 is relatively cheap).
You want a type of aluminium that is good to machine and works well for fabricate.
Use 7075 Aluminium Alloy if:
You needed a maximum absolute strength and hardness.
Your application is a high-stress or critical component (such as aerospace or competitive sports applications).
The part will be protected from corrosion with some type of coating (for example, anodizing).
Money is not a factor, and you are willing or are able to pay for a higher-priced product.
The component is mechanically simple and does not require a lot of forming or welding.
Conclusion
At the moment of truth in the 6061 vs 7075 Aluminium debate, there is no clear winner. It is about getting the right tool for the job. The 6061 aluminium alloy is the versatile, lower-cost, and corrosion-resistant workhorse that can be used for nearly any number of structural materials and general fabrication.
The 7075 aluminium alloy is the high-performance specialist that will give incredible strength and fatigue performance characteristics in the most demanding, high-stress situations, where failure is absolutely not an option.
It is crucial to identify the two different types of aluminium alloys in terms of their chemical composition, mechanical properties, and workability.
By comparing the requirements and needs of your project to the characteristics of these two high-performance metal alloys, you will have what you need to make a smart decision that results in a product that is strong, durable, and designed for its intended purpose.